THE UNIVERSITY OF ILLINOIS LIBRARY .-2. 1 UNIVERSITY OF ILLINOIS Agricultural Experiment Station BULLETIN No. 189 PARASITIC RHIZOCTONIAS IN AMERICA BY GEOEGE L. PELTIER URBANA, ILLINOIS, JUNE, 1916 CONTENTS OF BULLETIN No. 189 PAGE Introduction 283 General Historical Account 283 General Characters of Ehizoctonia 286 Distribution of Ehizoctonia in the United States 292 Distribution of Ehizoctonia in Canada 306 Distribution of Ehizoctonia in South America and the West Indies 306 Distribution of Ehizoctonia in Europe 306 Distribution of Ehizoctonia in India and Australia 308 Plan of Procedure ' 308 Symptoms of Ehizoctonia Disease on Various Hosts. . . 308 Inoculation Experiments 337 Discussion of Inoculation Experiments 358 Growth on Media 364 Measurement of Mycelial Cells 370 Soil Survey of Ehizoctonia 372 Parasitism of Rhisoctonia Solani Kiihn 375 Summary 376 Appendix 378 Bibliography 386 FIG. 1. CARNATION STEM EOT CAUSED BY EMzoctonia Solani PARASITIC RHIZOCTONIAS IN AMERICA* BY GEORGE L. PELTIER, ASSOCIATE IN FLORICULTURAL PATHOLOGY One of the most serious and troublesome diseases which must be contended with by carnation growers in this country is the so-called "stem rot" due to the fungus Rhizoctonia. In 1911 a study of this disease was undertaken at the University of Illinois by Mr. H. W. ( Anderson, at that time Assistant in Floricultural Pathology and now Professor of Botany in Wabash College. Since July, 1912, when Mr. Anderson left, a thoro investigation of those diseases of vegetable, field, and floricultural crops which are caused by Rhizoctonia has been conducted by the writer, the primary object being to determine whether infection is brought about by one or by more than one race or species of this fungus. The results of this phase of the work are pre- sented in the following pages. Extensive studies have also been made of stem rot, with a view to publishing at a later date. GENERAL HISTORICAL ACCOUNT The first description of Rhizoctonia was given by Duhamel, 33 who in 1728 found it causing a disease of saffron (Crocus sativus) in southern France. The diseased bulbs were thickly covered with a reddish vio- let network of hyphae which spread out into the surrounding soil, with knot-like swellings here and there in the mycelial network. Duhamel conceived these swellings (tubercules) to be the individual plants and the hyphae to be the roots, and named the fungus Tiiberoides. Almost sixty years later (1785) another French investigator, Fou- geroux de Bondaroy, 23 mentioned that asparagus that was grown on land in which diseased saffron bulbs had been previously grown suf- fered from this same disease. Bulliard 11 in 1791 numbered it among the Truffles and named it Tuber parasiticum. Ten years afterward Per- soon 82 placed the fungus in the genus Sclerotium and called it Sclero- tium Crocorum. De Candolle, 24 who discovered a similar disease on lucerne, gave to the fungus the name Rhizoctonia. Later he distinguished three species, R. Crocorum, R. Medicaginis, and R. Mali. Nees 70 in 1817 referred "The results presented in this bulletin formed part of a thesis submitted by the author to the Graduate School of the University of Illinois in partial fulfil- ment of the requirements for the degree of doctor of philosophy in botany, May, 1915. Revised to date of issuance. 283 284 BULLETIN No. 189 [June, to a fungus attacking crocus as Thanatophytum Crocorum. This ap- pears, from his description and figures, to have been Rhizoctonia. A new species of Rhizoctonia was described in France by Duby 20 as Rhi- zoctonia Allii on Allium ascalonicum. In 1843 Leveille 65 noted a simi- lar Rhizoctonia on Rubia tinctorum, Solarium tuberosum, Pliaseolus, and Tulipa, without attempting to place it under any particular species. In 1851 the Tulasne brothers 134 classified all the forms of Rhizoctonia as a single species, Rhizoctonia violacea, a classification which has been adopted by a number of writers. Rhizoctonia on cro- cus was reported in Germany in 1858 by Kiihn. 64 He also found this same fungus, which he identified as R. Hedicaginis, on sugar beet. At the same time he described a new species of Rhizoctonia on potato, which he clearly distinguished from the above species and to which he gave the name R. Solani. In the United States, Rhizoctonia was first reported by Webber 137 in 1890 on the roots of alfalfa in Nebraska. He listed the fungus as Rhizoctonia Medicaginis DC. The first extended account of Rhizoc- tonia in the United States was given by Pammel, 76 who found it caus- ing a serious disease of beets in Iowa. Later, Atkinson 3 observed Rhizoctonia causing damping-off of cotton seedlings, and following that, of a number of other kinds of seedlings. In 1901 Duggar and Stewart 32 added a large number of hosts subject to Rhizoctonia attack. Many observations of other hosts and in new localities have since been made until at the present time Rhizoctonia has been found on one or more hosts in practically every state in this country. It has also been reported from Canada, the West Indies, South America, India, and Australia, so that it may be regarded as a truly cosmopolitan fungus. Duggar, 8 in an article published since this manuscript was com- pleted, brings out the fact that the violet root felt fungus, commonly known in Europe and the United States as R. violacea, should be re- ferred to as R. Crocorum, (Pers.) DC. He states that unfortunately this name has priority over the more descriptive name R. violacea. Under R. Crocorum (Pers.) DC., Duggar lists the following pro- visional synonymy: Tuber parasiticum Bull. (1791) Sclerotium Crocorum Pers. (1801) Ehizoctonia Crocorum DC. (1815) Rhizoctonia Medicaginis DC. (1815) Thanatophytum Crocorum Nees (1816) Tuber Croci Duby (1830) Ehizoctonia Rubice Dene. (1837) Ehizoctonia Dauci Eabenh. (1859) Ehizoctonia violacea Tul. (1862) Ehizoctonia Asparagi Fckl. [non Fr.] (1869) Hypochnus violaceus Eriks. (1913) Duggar, B. M. : Ehizoctonia Crocorum (Pers.) DC. and E. Solani Kiihn (Corticium vagum B. & C.) with Notes on Other Species. Ann. Mo. Bot. Gard., 2, 403-458, 9 figs., Sept., 1915. 1916] PARASITIC RHIZOCTONIAS IN AMERICA 285 Under R. Solani Kiihn (Corticium vagum B. & C.), the form com- monly found in this country and to a less extent in Europe, and the name generally used by American authors, Duggar gives the following synonymy : Ehizoctonia Betce Eidam [non Kiihn] (1887) Ehizoctonia Napcece West. (1846) Ehizoctonia Eapoe West. (1852) Hypochnus Solani Prill. & Del. (1891) Duggar states further that with the evidence at hand a number of species of Rhizoctonia described from Europe may be excluded from the genus, while several species are doubtful. He adds that in all probability the six species described from America, listed in Saccardo, may also be excluded, altho a more critical study of material is needed. Many attempts have been made to connect the sterile fungus Rhi- zoctonia with a perfect stage. Fuckel 43 in 1869 stated that the ascomy- cete Byssothesium circinans Fkl. (LeptospJiceria circinans Sacc.) was the perfect form. However, beyond the association of these two forms on decaying stems of Medicago sativa, there were no signs of their con- nection. The same observation was also recorded by Prunet, 90 but again with no more conclusive proof than the presence of the two forms on the same plant. Massee 66 considered Rhizoctonia as representing the vegetative condition of Rosellinia, because of the fact that the struc- ture and color of the mycelium and the general habit of Rhizoctonia resembles that of the Rosellinia quercina Hartig and other destructive parasites belonging to that genus. He had no further evidence, how- ever, to support this supposition. During the summer of 1913, Cook, 20 while examining tubers af- fected with Rhizoctonia, found a sclerotium that contained a mass of well-developed asci bearing spores. The mycelium .of the sclerotium was characteristic of Rhizoctonia and the asci appeared to arise di- rectly from it ; this point, however, could not be determined with any degree of certainty. In 1891 Prillieux and Delacroix 89 described a basidiomycete, Hy- pochnus Solani, and altho at the time they did not associate it with Rhizoctonia, it has been accepted by a number of European writers in recent years as the perfect stage of R. Solani. In 1897 Frank 41 reported Rhizoctonia violacea as attacking grape- vines, and since a Thelephora was found associated with it, he pro- posed the name Thelephora Rhizoctonice. In 1903 Rolfs, 93 working with the Rhizoctonia disease of potatoes in Colorado, found constantly associated with this fungus a basidiomy- cete which Dr. E. A. Burt identified as Corticium vagum B. & C., var. Solani. He was able to trace the connection between the two forms, and completed his evidence when he obtained cultures of Rhizoctonia from single spores of the Corticium stage. 286 BULLETIN No. 189 [June, Eriksson 38 has described a new combination, Hypoclinus viola- ceus (Tul.) Eriks., which he believes is the perfect stage of Rhizoctonia violacea Tul. However, beyond association on different plants in the same field, he appears to have no further evidence to show that the perfect stage which he found on a number of weeds is connected with R. violacea, found on a number of root crops. GENERAL CHARACTERS OF RHIZOCTONIA The morphological characters of Rhizoctonia Solani Kiihn vary with the age of the mycelium. The young hyphas branch at an acute angle from the parent hypha, subsequently lying parallel to it. A constriction is shown at the point of union, and a septum is generally laid down a short distance from this point. The threads are colorless and vacuolate. With age the hyphae lie more at a right angle with the main axis, showing less constriction. They deepen in color into a yel- lowish and then a rather deep brown, becoming more or less granular and empty. (Fig. 2.) Fusion of hyphae is very common and can be observed in any young culture of the fungus. It occurs either between hyphae of the same parent mycelium or between hyphae from separate colonies (Fig. 2). On many hosts a short tufted or bushy growth of the mycelium may occur with some strains. This tufted growth is likewise present FiG. 2, (1) YOUNG HYPH.*: OP Ehisoctonia Solani; (2) OLD, BROWN, AND EMPTY OF Rhizoctonia Solani 1916] PARASITIC RHIZOCTONIAS IN AMERICA 287 in cultures of the strains that produce such growth on the host plants. The tufts are composed of brown hyphae, closely septate, constricted at the septa, and often branching in an irregular manner. Sclerotia in cultures first appear as small, soft, white masses of hyphae. Later they become larger and turn dark and hard. Study of sclerotia at different ages shows that they are of uniform structure com- posed entirely of masses of irregular and barrel-shaped cells which break up into sections of one or several cells (Fig. 3). These shortened hyphal cells function as conidia and germinate readily under suitable conditions. Germination generally takes place by the protrusion of a tube thru the septum of a cell where it has broken away from an adja- cent cell. In some cases the hyphse of the germinating cells pass thru adjacent cells, which are apparently empty. Occasionally these irreg- ular and barrel-shaped cells germinate equatorially instead of at the poles. After the germ tube has grown out some distance, it becomes narrowed near the germinating cell and a septum is laid down. The mycelium then develops in the usual manner (Fig. 4). The formation of sclerotia in nature is rather common on majiy hosts. The best known examples are those formed on the potato tuber. The size and shape of the sclerotia vary considerably. On potatoes they are small, about 1 to 5 millimeters, and are generally flat. On carnation plants they may reach a diameter of 5 to 8 millimeters. When the fungus is grown on soil in pure culture, they become 5 to 6 centimeters in diameter (Fig. 5). The sporiferous stage of Rhizoctonia Solani was first observed in this country by Rolfs 93 in 1903, on potato stems. It was described by Burt 94 as Corticium vagum B. & C., var. Solani" In Europe this same fungus is generally known as Hypochnus Solani Prill. & Del." Altho the writer has observed Rliizoctonla Solani on seventy-five species of plants, including weeds and field j vegetable, ornamental, and floricultural crops, growing under diverse conditions and at different times of the year, for the past three seasons, it was not until the spring of 1915 that he found the Corticium stage. It was then observed in his home garden on bean, beet, radish, potato, parsnip, carrot, chard, spinach, pea, plantain, and pigweed. This stage was also found on winter vetch growing on newly plowed land, on carnation plants, and on a number of annual and perennial plants. In some cases patches of soil well protected from desiccation were covered with the ashy gray mycelium of the perfect stage. In a recent letter from Dr. Burt, he states : " I do not now believe that there is even a varietal difference between Corticium vagum B. & C. and that on the potatoes ; hence I shall drop var. Solani. ' ' b ln his monograph on the Thelephoracece, Burt 12 limits Hypochnus to resupi- nate species with colored, echinulate spores, while under Corticium he includes species always resupinate, which have colorless spores and lack cystidia. Accord- ing to Burt 's classification, Hypochnus Solani Prill. & Del. becomes a synonym under Corticium vagum B. & C. 288 BULLETIN No. 189 [June, FIG. 3. (1) YOUNG, BARREL-SHAPED CELLS WHICH COMPOSE THE SCLEROTIA OF Ehizoctonia Solani; (2) OLDER, EMPTY CELLS FROM THE SCLEROTIA FIG. 4. GERMINATING SCLEROTIAL CELLS OF Shizoctonin Sohmi 1916] PARASITIC EHIZOCTONIAS IN AMERICA 289 290 BULLETIN No. 189 [June, The presence of the Corticium stage seems to depend on climatic conditions. A cool season with an abundance of moisture is appar- ently essential for its development in the field. This stage is gener- ally found on plant .tissues that are perfectly healthy ; it is in no way injurious to them. Some cases have been found where it had devel- oped on stems almost cut off by Rhizoctonia, but in no instance has the writer seen it form directly on a lesion or on injured tissue. (See Figs. 6 and 7.) The development of the Corticium stage may be described as fol- lows : The dark brown hyphae of the sterile stage gather, usually at the base of the plant, and from them arises an ashy gray mycelium, which forms a fine network around the stem. The development is usually faster where a little soil, thrown up by the rains, has formed a film around the stem. The extent of this fruiting layer varies, but it may proceed several centimeters up the stem. It is so lightly attached to the plant that it may easily be rubbed off. As it becomes old, it cracks and falls off. The outer hyphae of the fruiting layer bear club-shaped basidia with four sterigmata and spores. Cystidia are lacking. The spores are colorless, oval to ovate, and have pointed bases. The usual spore measurement varies from 9 to 14 /* by 6 to 8 /*. Cultures of Rhizoctonia from single spores of the Corticium stage have been obtained both by dilution methods and by the method used by Rolfs, 94 which consists in placing a stem covered with the fruiting stage over an open petri dish containing a nutrient agar, and allowing the spores to drop on the agar. Another fungus belonging to the genus Corticium, C. ochra- leucum (Noack) Burt (see footnote b, page 287), found in the United States by Stevens and Hall 117 ' 119 on pomaceous fruits, has been care- fully examined by the writer. The mycelium of this species corre- sponds in many respects to that of R. Solani and the development of the perfect stage is similar to the development of the Corticium stage of that species. It appears that these two species are very closely re- lated, but are entirely distinct forms. Duggar," who has had an opportunity to study R. Crocorum (Pers.) DC. more at length, gives the following description of this species in his recent work : "The external, general hyphae are more or less different in form and appear- ance with age. The younger hyphae are usually dilutely violaceous with a pigment which may be decolorized by the application of acidulated water. The protoplasm is dense towards the tips of branches and vacuolated farther away. The hyphae are somewhat flexuous, branched (sometimes closely), with the branches arising at right angles to the main hypha, and with a partition wall laid down at not over 10 fj. distant. With age the hyphae become rigid, somewhat less in diameter, 48 ft, the branching is distant, and these branches readily break off at the first partition wall. At the point of union the diameter is uniform with the main *See footnote, page 284. ID 16] PARASITIC HHIZOCTONIAS IN AMERICA 291 FIG. 6. GREEN TOMATO SHOWING THE SUPERFICIAL ASHY GRAY MYCELIUM OF Cor- ticium vagum B. & C. PRESENT AT THE POINT WHERE THE TOMATO TOUCHED THE SOIL FIG. 7. ENLARGED VIEW OF A SECTION OF FIG. 6, SHOWING THE DARK STRANDS OF HYPH^E AND SMALL, SPHERICAL, BROWNISH SCLEROTIA OF Ehizoctonia Solani KUHN WITH THE ASHY GRAY NETWORK OF MYCELIUM OF Corticium vagum B. & C. (5x) 292 BULLETIN No. 189 [June. hypha. The partition walls are distant, often 120-200 /j. apart. The walls now possess the violet-brown pigment and in the lumen little or no protoplasm is ob- servable. "The internal mycelium is likewise branched, septate, often associated into loose strands, passing between the cells or traversing them. In the early stages of the disease, so far as reported, these internal hypha3 are nearly colorless and are generally of less diameter than those constituting the external mat. " the hyphae constituting the external mantle may be uniformly dis- tributed, as is the case usually when the fungus attacks fleshy roots or tubers, or they may also form a number of aggregates having the appearance of loose or root- like strands." The infection cushions are distributed over infected roots. ' ' The external hyphae are for the most part similar to those of the general mycelium, but there occur also branches in which the cells are short and swollen, sometimes resembling a short chain of spores The medullary portion of younger cushions is made up of finer, almost colorless hyphae, and it is this type which enters strand- like the cortical tissues of the root, destroying particularly the cambium and younger phloem regions. In the later stages of development it will be found that the cushions seem to extend considerably into the cortex, and more of the hyphae are colored." ' ' The true sclerotia are flattened or rounded bodies varying in diameter from a few millimeters to several centimeters. When mature they are of a deep violet- brown and are thickly clothed with a persistent velvety felt, externally of the same color as the root-investing hyphae, but ^darkening further in. Among the surface hyphae of the sclerotia as well as of the 'infection cushions' are found chains of enlarged cells quite distinct from the enlarged cells of E. Solani. The sclerotia, as noted previously, are always connected with the root felt by large hyphal strands. " a sclerotium consists of fairly compact tissue made up of cells often considerably branched and sometimes curiously lobed." DISTRIBUTION OF RHIZOCTONIA IN THE UNITED STATES In Table 1 is presented a list of those species and sub-species which have been reported as being susceptible to R. Solani in the United States. It is obvious that as long as investigations on this dis- ease are continued, such a list cannot be regarded as complete or final. It may be noted that plants belonging to the families AmarantTiacece, Caryophyllacece, Cruciferce, Leguminosce, Solanaceoe, and Composites are especially susceptible to this fungus. Under favorable conditions it can attack plants in these families at any stage, from seedlings or cuttings to older plants, when grown either in the field or in the green- house. About fifty important families of flowering plants are repre- sented, several gymnosperms, and Equisetum, one of the Pterido- phytes. The list includes a number of monocotyledons, which for- merly were reported as being not susceptible to Rhizoctonia. Among the dicotyledons are many annuals and perennials, including herbs and woody plants, as well as most of the greenhouse and garden plants, field crops, and weeds. R. Crocorum, as will be seen in Table la, has been reported so far in this country from only a few scattered states. It is probable that as investigations continue this fungus will be found in many other localities. 1916] PARASITIC RHIZOCTONIAS IN AMERICA 293 s 5* 2 M Q} ^5^ 03 O! (B ^bX,* .9 .1-1 o o A be 0> 3 S S ~ "" " o be - - P S ft 03 Q a. coQooQ bfi^ be BOS . i. ._. C '** Q " S o B 03 o 03 PMP 2 e 02 -- CO ^ S W go II f OQ W 02^ fd TJ * g '> 'o ' CO P-i Pn AH DS S IfJls>l < 'J iJi-9.ip^ii ^'o S c be 1 M ?s * ^ - r ** S .3 'ri s . ftGO. i ? en cZ f^ 294 BULLETIN No. 1.89 " be o p, 3o * . . S.S, . . * . . ., . ti) rS~---.2 T3 " ~ ^2 Ol o M S"" MO MQ Q(J 03 C3 .2 .2 ^^ 5 QO w o o PQ 1916} PARASITIC RHIZOCTONIAS IN AMERICA 295 -S . o SIP *< w If" COP . * ^ ' OqjO -gbc a -gbc a OJO ^-bo oc ' bc GO _, -^ _, Sg-Sg .JJa! ^cs GOQ QC P P' J < W 3=313 CO 173 O etf 00^ T3 ^ pS CS t.. 1* s 296 BULLETIN No. 189 [June, CO OQ DO ep CB 3 oo O ^~, s~* O 3 P ^3 O a ^~^ 1 V Oj 3 .^^^ ^^^ W CO" PH 3 bO 3- 0""""^ C^bi) bo ti V|\ ^ ' ^ ** S J ^"^ ^ ^ bO S x-^ * 0) 00 m M li 00 bO f-. bo bo bo bO oo 5? , 1 .5 W ^^ fd^.S^^^ .S p 5 O ^ .s ~ '-^ *^ f3rs*r*s Q*^ ^M ** ^ ** j~^ . **^ ^S V 4) S ** OS 03 (p ** s o 03 s ^ X- i: 00 "^ "^ ^ QQ "^ ^^ r-H*v*v*v*\ T?** ""O oo ^ o 01 o PH Q ^^' ^O**^^ C^*xss*v Q} ^ ^ 03 fcyojH^ ^-^ ' h-j f rH . C(3 "-^ ft-j ^ * *\ f-~* j4^ fpt yn ^ ^ -= *"""' O -4-3 <*. s O '^-^ ' ^^, *~ ' ^~^ O *-s Ci** O " " *^ bo +. f. ,, <* -^ If bo :^ .g g^: 2: :: : 2s .s -f bo-^> bo fl >H .S * .5 '| S 4- a s a a a a ~ ^ 2 5 O 03 rH c p| OQ POQ 02 GO P GO P&Q P J_!> ** C s ? fl O> A ! 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Qj *s *^ t< 3 . a> - -- * *j ;* 1^2 M CP - - 2 | |*J l:-| '1 S^ s ii^ ^ *]g fl <3 oo (,O CS oo o S tS* bd o * 298 BULLETIN No. 189 [June, b s r^ .2 m o >H 5 t> cS 00 bo _g -3 0> on x^s r3 ?a 13^ ~ 2 ? ? 'S ' S3 s J s " : - g~ g 3 ^ g ^5 S S cOtn -tjaioToo ojoa bDbc gbObcbOrofcjDbo fl rtpc-aiobo^'q a " a a * * > "p Vi o> 01 'QJ^^' 01 o) W s^^ 02 ^ CO 02 p- ^^3 00 C? CO o ^f3 bo ^ 2 c^ bo oj bo ^^j bo *? bo a-(j bo bo fl a O p flfl-"oq a PH T3 PH M ^ TH M -PH > M .p-l .^H O OS O~ WO M s- -g s- - - ^ |-gs-|s = -ss g w O Co O ,4.3 O Cd ^ Q O 03 03 f^ OH f***l 05 o^ 05 Q 03 Q ^^ 05 C*\ Observer h 6 GQ CO n3 * a ro 03 b C3 2 s''o : f;'o ; f O2 ft P3 QQ P3 O2 g s 13 11 l^'fl*. lsS* J 8 *g s fe ESi-HplH-is*^ O^ ^^^Ccfl'a*^j F 2 *-Jj co * t3 -^ fl > *^j ** " (jj '^o 1 ^^ -^pfd ^^^S r o*S P ~^S'~~'^ < ^ r fl5*' *^ Oi*" 1 ^ ~* 02PQ^pR Qi-^ O^CCHHOAnHPki-sQpH ^GQp^ 5 O iH CM CO 1C CO O3 occcqcq^co^TH^^o^^oo^^coco^co^TtrH^^^ 03 O5 O) O5 O) O3 O5 O5 C5CiC5C5GiO^dOiCiOO^CSCiC3O^O^CiOiCiCiOiO^Ci^'. C^Ci Hi ~S 02 j-B " >H 'O cS ? r rt ^ g T3 .SP 1 fc^.s'g.s-g * >^ ja J2 ua > OS ^ 2 g H ^rt"3 0303 a* 0) * ' tn O M o SJ >> "g "e cc ^j fi S i-l e ?a ^ ^ ^ ^ ^ ^^^^^^^^^^.^^^ ^ _ 1J .T 1 a a> ., . I K; H HMH -H o 1 1916] PARASITIC EHIZOCTONIAS IN AMERICA 299 Character of injury Stem rot (greenhouse) Damping-off, seedlings (greenhouse) Kosette (field) Fruit rot " > > } > ) > Eosette ' ' )> Damping-off, seedlings Damping-off, seedlings Fruit rot (field) ) ) ) > f ? ? O O 3 s~ -s _s o n 9 a W fl v^5 ^5 ^ So | | ft & | .5 .9 o Q tUO tUD -4-) fcUD-4J fcJD^^ *"> "^ tlC'rt rrt tlfir^ -t- ** ****** *j ** (H *rj ^ *^ ^H . B ^H f^ ** FH ^ ^ OCoGOQO-*flj n}\ ^O cd Cj OrtOCOO^OCCnj Q)*t.CQ^O P P WPMPMOKP02 02 P02P3 Observer JM 'o ^ H T3 ,0 O fl P OS JL ^> g* !S2 IJti 3- ffii iiJ'Si fL| GOfSPLiO 02WK^i> ^o^irjw O-M -^SQ?OJ^-^ F^H^^OJO*^-^ Qi-sfflKCM 03 02 02 PH 1-5 pq O O 02 O 02 i-s O 02 9 ^^cOLOt^OOrH^-ICOCO^ ^^^^^^^OOQOJO^^^^^^^O^^^CC a 05C5 SSoOJOSOsSoiOSOi 2SSS2SSSSSSSa OS :;:-:::: : ::::: H Q S I o t2 IS ' ---~ 0123; cs^^^^w, . -4-> p t W 'S ||| i * a s 1 -S- ~ ^.. * ** ^" * - * *N "V 111 1 1 300 BULLETIN No. 189 [June, tUO^j bO I s -a: en QWQ e ** o fl < 9' n coO bC -2 r pq ai Illllll e f 1 a-e = lllalJI- J !o s oi - : S 5 e 2 1916] PARASITIC BHIZOCTONIAS IN AMERICA 301 1 "0 f ^ ii 65 POOQ -^ bo g ^ tuo -9 2 229- S '^^ -&| S ^, <*" Ilili . - liiPlliill'Siii 55 ATE i M ^ jzr5zr a S ^ S 5 &H RH ft? PcJ 302 BULLETIN No. 189 [June, Character of injury ^-* S O rs " ' "3 " be i 1 && x v O Q LJ r3 r3 5 43 3 s 1 ~3 I H 3. 00 r^ ^ 00 * " JH~ "3 o> ^ JM"" ^T S _M o" 2 1 .2 * 2 ... *"* OJ K g -M 4J el i 2 U0> Q MM P ' cuttings " seedlings Stem rot (greenhouse) Damping-off, cuttings (greenhouse) " seedlings Stem rot (field) Damping-off, cuttings (greenhouse) ' ' seedlings On roots (greenhouse) Damping-off, seedlings (greenhouse) i ) } > > > ' > o o ,a a S O) So ^^ 01 ^ oo oo f be be ^ 2 -5 - ^5 M r^3 r, rn > O - fl} & ^B" O * C^ & T3 CQ 'v 4i "* - " "* "-, T3 >_- ? --v_ ? - a^ -*-j v bC *-" bD 2- .2. : 2.2. : *ir ^ f F *. o tn cs ~ a ^ Observer -4J -4J + b & t- 03 OS OS 1. I S V V O> +J 4S *J QQ CO OQ * 1 H t*]f CO 83 ,, ^3 H TO |jq a3|jt> "o^-Sji^ * a - o ** O &H 00 ^-^^ ^^ OQ * > Boo ' (2 ^w t a i~ H QJ " 1 I -c * a~ a g os" a >-. " tH >-l +J O WOnWOn^ H^P S rH^llO^^|(M S ~ H * '2 02 a co : S= I i to *u - to si . s~ ^ > . ** . o =C S* U 4S JXP^^S 1 . M w 1!1 " | & ec: ^ |f& 1 I i a 5 .s ^ 5 ft^'S e^g^ v ^ Q Q X *+0 O <5 on l ^ a o ^ 5^ f*" ^ "^ -SoS^sS? ^a *" - ,Z: f^a f^. ^- - 1 ^e ^^ g .>> to ^3 |j -If Sr : g- ^: ^ -S -S s s So ft^ (^(^ft^ (^ &5XJ : : 1 ll : llll" &a i/j OQ OQ &a &Q 05 1916] PARASITIC KUIZOCTONIAS IN AMERICA 303 O f 1 ^ ^ ^ a) -4J ss 2 Mcc I .5 fl O 3 m O I .. el i el 9 X OJ (M O O Oi O^ Oi O Ci O5 Oi ~. _._.*. ~. *._._. ~. r. r. r. - 304 BULLETIN No. ].s;i [June, b a '5 s pH H O 1 t> 2 (field) (field) seedlings (greenhouse) > > j i dants (field) cuttings (greenhouse) > > p on 02 * 1 1 SB H o> a; j^ q} CU 3 ' & 3 Sr'^ CD <. > N^' O S^X^" X O **-S O ^~^ "g^ : ^ ^ .9"^ .2 ^.9 2^ +* fi -^ C - 1 - 3 C S o. ... go. S o g g- O~-*N*^ TOON w o OQ ^ ^ p^ Q PH f*l P^ O OC Damping-off Stem rot (gi Damping-off Observer * * * O3 * CD 2 * * H w H *-> Spq^oSjS >?6p^wp^o Peltier > > > ! e s f CO fe m *2 g OQ 1* s * 1 1 ^ 1 S 1 3 ^ " 1 F.I "3 1*5 PH 02 HS _ . _. r. os C5 o Ci O) Oi O Oi O^ C* C 1 Oi Oi O" C-CiO^OiOCiO^CiC^C^C^iO^C^C^ ~. ~* . . H J a * 1 8 (H 1 .S g 73 .3 B | 03 {j LM .Sp| - .| s . g || "i | a to o - - B M CIS o -s .2 | ^-a s -a ^gfl totn O^MCC^O: Wisconsin . . Illinois : : : S s ^H %~ ~ I Ks O. _ ^5 O PS p^*** S - g * ^ g o - S | : !" - - * ii : ** w ?= * ~ ^ *" * .^-S -"s " : : : p-t PARASITIC RHIZOCTONIAS IN AMERICA 305 be to .9 "o '& o S * as a PO * 73 a cS * DO -C *H S 3 w ." a> be ,a fe be!ti 3^ ^5 r3 o cs a> eoMPnEHCM Ok Ok Ok OO r B cs M !2 .rt CO CS CO S 'g 1 .9 5- e " to ^ ^ fc. tsj P 0} w ** bo o ^tf~ -M ^ o * AH -u cp fl cS . CO O IH CP PnOQ 306 BULLETIN No. 189 [June, DISTRIBUTION OF RHIZOCTONIA IN CANADA In a letter to the writer, Dr. H. T. Giissow of the Central Experi- mental Farm, Ottawa, Canada, stated that he had observed Rhi- zoctonia Solani on potato, pea, sweet pea, and aster. That the stem rot of carnation also occurs in Canada is shown in a paper read by John Morgan of Hamilton, Ontario, before the Canadian Horticul- tural Association at Guelph, in August, 1906. DISTRIBUTION OF RHIZOCTONIA IN SOUTH AMERICA AND THE WEST INDIES The following list of plants reported as susceptible to 'R. Solani in South America and the West Indies, with character of injury, has been compiled from Cook's 19 Diseases of Tropical Plants: Bean Damping-off, dry rot of stem, and pod rot Beet Root disease Cotton Damping-off and sore shin Cucumber Damping-off Lettuce Damping-off Melon Damping-off Nursery stock Damping-off Pea Root and stem rot Potato On stem and tubers Seedlings Damping-off Sweet potato Root rot Tobacco Seed-bed rot Tomato Rosette and fruit rot DISTRIBUTION OF RHIZOCTONIA IN EUROPE Despite the wide distribution of Rhizoctonia in Europe, the nomen- clature of the species is in a very confused state. Some writers under- stand Rhizoctonia Crocorum (Pers.) DC. to include several species, while others treat it as a separate species including forms with a rich violet mycelium. This uncertainty extends to the other common species of Rhizoctonia, so that the European literature on the subject offers many difficulties. Another fact which adds to the confusion is that both Rhizoctonia Solani and Rhizoctonia Crocorum attack potato stems and tubers, and while the symptoms caused by the two fungi can be easily distinguished from one another in the field, it is another mat- ter to differentiate between them in literature. A partial list of the hosts in Europe which are attacked by Rhizoc- tonia is given below to show the extent of the distribution of this fun- gus. Only the more important references are mentioned. Austria Hungary. Rhizoctonia was first reported in Austria Hun- gary in 1875 on potato. Later 7?. Crocorum was found on sugar beet, potato and lucerne, and R. Solani (Corticium vagum), on potato. 1916] PAKASITIC RHIZOCTONIAS IN AMERICA 307 Belgium. R. Crocorum has been observed in Belgium on sugar beet, potato, and asparagus. Denmark. E. Rostrup, 96 ' 97 during the years 1884-1905, reported Rhizoctonia in Denmark on a large number of hosts, including many weeds and the roots of several species of forest trees. Among the cultivated crops mentioned are carrot, clover, lucerne, kohl-rabi, beet, turnip, sugar beet, and potato. Both R. Solani and R. Crocorum were observed on the potato. In 1892 Rostrup described a new species from turnip, which he called Rhizoctonia fusca and which differed only in one or two essential characters from R. Crocorum, also found on turnip. England. Rhizoctonia was first reported in England on mangel in 1901, and on potato in 1904. The next year Gussow, 48 in an ex- tended account of this disease, stated that it was due to R. Solani. Salmon, 101 in working on a disease of seakale due to R. Crocorum, found that it was also able to attack salsify, parsnip, carrot, parsley, lettuce, and potato. Finland. Reuter 91 has studied a Rhizoctonia in Finland which causes a root rot of rye. R. Crocorum has been found on beet. France. Between the discovery of R. Crocorum in France in 1728, on crocus, and 1851, a number of hosts, including asparagus, bean, clover, Citrus, Coronilla, grape, onion, Rubia, Sambucus, and tulip, were reported. Germany. In 1858 Kiihn 04 found R. Crocorum on sugar beet in Germany and described the species R. Solani on potato and carrot. Eriksson 38 states that in Germany in 1893 R. Crocorum appeared on sugar beet in several places ; on lucerne, in 55 localities on plants 1 to 5 years old ; on potato, in 11 localities ; on asparagus, in 3 locali- ties ; on hop, in 1 locality ; and also on a few weeds, such as Taraxacum officinale, Convolvulus arvensis, etc. ; and that in 1894 it was observed on lucerne, in 77 localities; on potato, in 11 localities; and on red clover, in 8 localities. The species R. Solani (Corticium vagum) and R. Strobi Scholtz on white pine, have been) recorded. Holland. Dr. Johanna Westerdijk reports both R. Crocorum and R. Solani as being very abundant on potato in Holland. Ireland. Peihybridge 83 ' 55 has shown that both R. Crocorum and R. Solani are present on potato in Ireland. Italy. R. Crocorum has been reported at various times as present on alfalfa, sugar beet, clover, asparagus, carrot, parsley, chard, the roots of grape, and many weeds in Italy. Rhizoctonia destruens Tassi occurs on the roots of Delphinium. Portugal. The Rhizoctonia attacking sugar beet has been reported from two localities in Portugal. Russia. R. Solani was reported on potato in Russia in 1899. 308 BULLETIN No. 189 [June, Sweden. Eriksson 37 ' 39 observed a disease of carrot and beet in 1898 in Sweden, caused by R. Crocorum. He was able to inoculate this fungus on garden and sugar beet, alfalfa, potato, and many weeds Stellaria media, Myostis arvensis, Galeopsis, Titraliit, Erysimum clieiranthoides, Urtica dioica, and Sonchus sp. In addition to these hosts Eriksson has reported R. Solani (Corticium vagum) on potato and R. Crocorum on turnip and kohl-rabi. DISTRIBUTION OF RHIZOCTONIA IN INDIA AND AUSTRALIA Shaw, 109 working on the morphology and parasitism of Rhizoctonia in India, reported Rhizoctonia Solani on peanut (Arachis hypogoea), cowpea (Vigna catjang), jute (Corchorus capsularis), Dolichos Lab- lab, Trichosanthes cucumernia, soybean (Glycine soja), mulberry (Morus alba], sesame, melon roots, cotton, roots of Agave rigida, and potato. In Australia, Me Alpine 07 found R. Solani very widely distributed on potato. PLAN OF PROCEDURE The main object of the present research was to determine whether of the culturable forms of Rhizoctonia one or more than one race or species is present in this country. The work was taken up from the following standpoints : 1. Symptoms of Khizoctonia disease on various hosts 2. Inoculation experiments 3. Growth on media 4. Measurement of mycelial cells 5. Soil survey SYMPTOMS OF RHIZOCTONIA DISEASE ON VARIOUS HOSTS Following are presented the observations of the writer concerning the nature of the diseases caused by Rhizoctonia on the various hosts, together with the principal facts which appear in literature regarding Rhizoctonia on the more important crop plants in this country. ALFALFA, Medicago sativa On March 17, 1914, the attention of the author was called to the damping-off of young alfalfa seedlings in the agronomy greenhouse of the Station. Microscopic examination and pure cultures showed it to be due to Rhizoctonia. The seeds had been sown in rows in pure quartz sand and kept well moistened. The young seedlings, on ger- mination, were somewhat crowded, so that the conditions were very 1916] PARASITIC EHIZOCTONIAS IN AMERICA 309 favorable for damping-off. The fungus could be seen extending in all directions over the surface of the sand. The fungus found on the diseased alfalfa seedlings was compared with a fungus obtained from mature alfalfa plants sent from Iowa. Altho the mycelium of the two forms was characteristic of Rhizoctonia, it differed in many respects, particularly in the color of the hyphae. The form on the mature plants was undoubtedly Rhizoctonia Cro- corum, while that on the seedlings was the common Rhizoctonia Solani. Rhizoctonia was first reported on the roots of alfalfa from Nebraska in 1890, by Webber, 137 as Rhizoctonia Medicaginis DC. This fungus was next mentioned on alfalfa as Rhizoctonia violacea, by Heald, 57 who found it causing a root rot in a single locality in Nebraska in 1906. In 1908 it was reported by Freeman, 42 under the name Rhizoc- tonia violacea, as spreading rapidly in the alfalfa fields in Kansas. Freeman described the disease as beginning in different parts of the field where at first a single plant dies. From these centers of infec- tion the fungus grows in all directions thru the soil, killing the plants as it proceeds. Thus circles of steadily increasing radii are formed, at the edges of which plants in all stages of the disease are found. The great majority of the plants within the affected areas die, while those which survive are not vigorous and always lose their main tap roots. The first external sign of the disease is a yellowing of the plant, which soon after wilts and dies. The roots of a dead or dying plant are found to be covered with a violet or brownish red mat of mycelial strands, or hyphae. In a few cases the tap root is completely rotted. In less severely affected plants, the cortex of the roots slips off easily when the plants are lifted from the soil, leaving only the central woody cylinder. This condition is due to the fungous threads which grow thru the cortex as far as the cambium layer, which they kill. The fungus forms sclerotia, which may live in the soil for several years. Stewart 126 in 1908 mentioned a root rot and damping-off of alfalfa in the field in New York. His description of the disease agrees in some respects with the one given by Freeman. Later he also noticed the damping-off of alfalfa seedlings in the greenhouse. He was not certain that Rhizoctonia Crocorum was present in New York, and was of the opinion that the fungus causing the damping-off of seedlings in the greenhouse was different from the one found in the field. Heald, 58 in a later article (1911), described more fully the disease occurring in Nebraska. At that time he regarded the fungus as iden- tical with Rhizoctonia Medicaginis DC. of Europe. From the above accounts it is certain that there are two species of Rhizoctonia in this country able to attack alfalfa R. Solani, widely distributed, causing only a damping-off of seedlings, and R. Crocorum, with a limited distribution, attacking as a rule only mature plants in the field. At present this latter species has been reported on alfalfa from Nebraska, Kansas, Iowa, and Virginia. 310 BULLETIN No. 189 [June, ALTERNANTHERA, Telantliera sp. In the fall of 1912 cuttings from alternanthera, coleus, and salvia plants which had been placed in the same bench were found to be damping-off. A microscopic observation and pure cultures from dis- eased cuttings showed that RMzoctonia Solani was the causal organism. Later the fungus was found on alternanthera plants in the field, but apparently it caused no injury there. Alternanthera plants grow low and bushy, and thruout the sum- mer, no matter how dry the season, the soil underneath is usually moist. On close examination of the tangled mass of branches, strands of a fungus, which were later found to be made up of bundles of hyphae, could be seen spreading in all directions. At first glance the masses of mycelium looked very much like old spider webs. A number of different varieties of alternanthera were examined, and all were found to have the characteristic brown strands ramifying upon the surface of the whole under side of the plant. The reddish varieties seemed to have more of the fungous strands than did the green and variegated plants. Cultures from the brown strands in every case yielded pure cultures of Rhizoctonia which corresponded morphologi- cally and physiologically to the Rhizoctonia obtained from the cut- tings. Whether the fungus was at any time parasitic on the plants in the field was questionable. However, cuttings made from them still con- tained pieces of mycelium, and when placed in sand in the greenhouse, the fungus did parasitize not only the alternanthera cuttings but others as well. The belief that Rhizoctonia is present on the branches of the alter- nanthera plant thruout the year was corroborated in 1913 and again in the fall of 1914, when the cuttings made from plants in the field began to damp off in the cutting bench. Repeated observations showed that the fungus was present on the plants in the field, notwithstanding the fact that they had been planted in new soil. Old plants brought in from the field were cut close to the roots and planted in flats in the greenhouse. These sprouted and developed new shoots, from which cuttings were made. Many weeds came up in the flats during the win- ter, and in March both the cuttings and the weeds became infected with Rhizoctonia. It seems, therefore, that the fungus is present on alternanthera at all times of the year, tho the only injury it causes is damping-off of cuttings in the greenhouse. ALYSSUM, SWEET, Alyssum odoratum During June, 1914, when the bedding and decorative plants were being set out from the floricultural greenhouses of the Station, about 1916] PARASITIC RHIZOCTONIAS IN AMKRICA 311 twenty-five plants of sweet alyssum growing in two and one-half inch pots were found to be diseased. The plants were tall and had fallen over from their own weight, so that they formed a mat over the pots. On close examination the soil and plants were found to be covered with the strands of brown mycelium which are characteristic of E. Solani. A number of these plants died, while on the stems of others the fungus formed small lesions near the surface of the soil. The fun- gus continued to grow on diseased plants placed in the field, and killed a few more of them. AMARANTHUS Specimens of Rhizoctonia on AmarantJius retroflexus were received from Mr. W. H. Burkholder of Cornell University. The mycelium of the Corticium stage could be easily recognized on the stems, while the Rhizoctonia stage was plentiful on the lower part of the plant. A cul- ture was obtained from scrapings made from the mycelium of the Cor- ticium stage. Several spores were found and one basidium showing the four sterigmata was observed. Duggar and Stewart 32 reported the occurrence of Rhizoctonia on Amaranfhus retroflexus (pigweed) and A. albus (tumble-weed) in New York in 1901. Several years later Rolfs 95 found the perfect stage, Corticium vagum, in Florida on A. retroflexus and A. spinosus. ASPARAGUS, ORNAMENTAL, Asparagus sprengeri Duggar and Stewart 32 observed the effects of Rhizoctonia on a number of plants of ornamental asparagus. They found that the plants were killed and that many of the leaves were bound to each other by the brown threads of the Rhizoctonia hyphge. ASTER, CHINA, CallistepTius Jiortensis Damping-off of aster seedlings was noticed in flats in the floricul- tural greenhouses in the spring of 1913 and again in 1914. The dis- ease first appeared as a small, brown spot on one side of the seedling at the surface of the soil. This lesion increased in size until the seed- ling fell over. After a number of seedlings were prostrated, the fun- gus spread over them, and in time a mat of mycelium covered the sur- face of the soil. In May, 1914, a number of aster plants, four to five inches high, were planted in old soil in which several varieties of carnation plants had been growing during the winter. There had been more or less stem rot among these plants all the season. After a month, when the aster plants were about 6 inches high, they began dying off and con- tinued to die until they were from 9 to 12 inches high and ready to 312 BULLETIN No. 189 | J tine. bud. Other aster plants set in new soil at the same time that these were transplanted developed normally with no stem rot whatever. TABLE 2. MORTALITY .OF DIFFERENT VARIETIES OF ASTER GROWN IN OLD CARNA- TION SOIL INFECTED WITH Khizoctonia Solani Variety Number of plants Total dead Total healthy Queen of the Market 50 1 49 Lavender 50 1 49 Azure Blue 50 4 46 Purple ' 50 7 43 Pure White 100 13 87 Shell Pink 50 2 48 Eose Pink 50 50 Deep Eose 50 50 Crimson . . 50 1 49 As can be seen from Table 2, plants from all but two of the varie- ties died in the bench. The varieties Azure Blue, Purple, and Pure White were planted where most of the stem rot on the carnations oc- curred ; hence the higher number of diseased plants in those varieties is due to location rather than to varietal susceptibility to Rhizoctonia. Obviously the Rhizoctonia causing carnation stem rot was in this case able to attack healthy aster plants. The stem rot of these plants was typical and very similar to the rot of carnations. The first sign of the disease was a yellowing and drooping of the foliage, followed, sooner or later, depending on weather conditions, by a sudden wilt- ing of the whole plant. When the plant was pulled, the bark of the stem near the surface of the soil would slough off, leaving only the dis- colored woody tissues. A stem rot of aster due to Rhizoctonia has been reported only once before in this country. Duggar and Stewart 32 in 1901 found the my- celium in the tissues of aster and later isolated a pure culture from them. They observed the disease in a number of localities in New York during that summer. BEAN, Phaseoliis vulgaris The damping-off of young bean seedlings by R. Solani, which has been observed in the greenhouse and in the field, is characterized by the production of small lesions at the surface of the ground either on one side of the stem or girdling it, followed by the falling over and death of the seedling. When the fungus attacks older bean plants, lesions of various sizes are produced just below the surface of the ground, at the surface, or one or two inches above it. In some plants these discolored spots can be found on the larger roots also. The lesions, as a rule, have a 1916} PARASITIC EHIZOCTONIAS IN AMERICA 313 FIG. 8. STEMS OP MATURE BEAN PLANTS WHICH HAD BEEN PLACED IN A BENCH IXFECTED WITH Ehizoctonia Solani ORIGINALLY OBTAINED FROM CARNATION PLANTS reddish brown band with a lighter colored, sunken area, and extend thru the cortical layer into the woody tissues. As on the young seed- lings, the spots are usually localized on one side of the stem, but in some cases one lesion may girdle the plant. These lesions weaken the stem and cause it to break off easily. The first account of Ehizoctonia causing a disease of bean was given by Atkinson. 4 He reported that during the winter of 1894-95 it caused damping-off of bean seedlings and attacked plants that were from 6 to 10 inches high. He referred to this form as "the sterile fungus," and stated that its most characteristic peculiarity was the mode of branching. In 1901 Duggar and Stewart 32 reported this fungus, from New York, as the cause of a stem-rot disease of red kidney beans in the field and of a damping-off among seedling beans in the greenhouse. 314 BULLETIN No. 189 [June, In 190-1: Hedgcock 60 reported as follows: "The bean crop in the vicinity of St. Louis was severely injured by a Khi- zoctonia which attacked the stems and large roots of the plant and also produced brown sunken areas on the surface of the pods, penetrating the latter and discolor- ing the seeds. An examination of a number of seeds whose surface was discolored, disclosed the fact that the mycelium of the fungus had established itself in the second coat and in many instances had formed minute sclerotia there without rot- ting the seed or even penetrating the cotyledons. The presence of the fungus did not prevent the germination of the seed. ' ' Fulton 44 in 1908 showed that Rhizoctonia from infected pods caused damping-off of seedling beans and of month-old plants. A serious outbreak of the stem rot of beans was reported from New York by Barrus 9 in 1910. He found that in some fields as many as 30 percent of the plants were infected. In the same fields during the following season it caused the, death of at least 5 to 6 percent of the seedlings ; later in the season, after a rainy spell, a large percentage of the pods in contact with the ground became infected. BEET, Beta vulgaris Young seedlings of the garden beet, in flats, were found damping off in the vegetable-gardening greenhouses of the Station, July 10, 1913. Cultures showed that R. Solani was the sole cause of the dis- ease. Characteristic lesions were found on the beets at the surface of the ground, and strands of mycelium could be plainly seen spreading out on the surface of the soil. As with root rot of other fleshy crops, the fungus gains its first held at the crown of the mature plant, which, as a rule, is just below the surface of the ground. The first evidence of the disease is a darkening of the leaf bases, followed by the rotting of the crown. The leaves retain their color for a long time, or until the leaf stalks rot off almost completely. With the rotting at the crown, the beets begin to crack from this point. While the tissues around the cracks remain firm, as a rule, for a long time, the crown is usually soft, a condition due to the entrance of other organisms. Lesions are some- times formed on the sides of the beets, often extending deep into_ the tissues. When weather conditions become unfavorable to the fungus, the rotting and cracking stops and the plant may recover from the attack. The disease is generally scattered thru the field, only a few plants in a given area being affected. Under the name Rhizoctonia beta? Kiihn, Pammel 70 in 1891 de- scribed a root rot of sugar beets. He was the first investigator to re- port serious damage caused by Rhizoctonia in this country. Duggar 28 in 1899 regarded the root-rot disease of sugar beet due to Rhizoctonia as one of the important diseases of that plant. At the present time this disease is very widespread and is the cause of considerable loss, especially in irrigated regions. 1916] PARASITIC UHIZOCTONIAS TN AMERICA 315 FIG. 9. GARDEN BEET INOCULATED WITH ' Bhizoctonia Solani FROM CARNATION, SHOWING A LATE STAGE OP INFECTION (Experiment 8) Damping-off of sugar-beet seedlings has been reported by Selby, 108 from Ohio, and by Smith, 113 from California. BEGONIA Mr. H. W. Anderson in 1911 found a number of begonia cuttings in the floricultural greenhouses that were damping off badly because of Rhizoctonia infection. The symptoms were similar to those described for cuttings of alternanthera. Damping-off of begonia cuttings has also been observed in New York by Duggar and Stewart, 32 and in North Carolina by Stevens and Wilson. 122 BLACKBERRY, Eubus sp. Root disease of blackberry and raspberry caused by Rhizoctonia has been reported only once in this country. Paddock 7r> of Colorado, who studied this disease, described it as follows : ' ' The trouble was first noticed by the foliage becoming light green or yellow- ish. Later in the season leaves on occasional plants began to curl and shrivel as parts of the plant below ground were attacked, but the greatest injury occurred on the canes above the crown. Here the bark was discolored and shrunken from the crown to the surface of the soil, or a short distance above. The fungus grew out within the bark, destroying the tissues, and interfering with the movements of plant food. The injury commonly extended around the cane, and when it became deep enough to cut off the supply of moisture and food, the plant died. ' ' BUCKWHEAT, Fagopyrum esculentum In 1911 Stevens and Wilson 120 ' 121 mentioned a serious outbreak of Rhizoctonia on buckwheat in the western part of North Carolina. No description of the disease was given. 316 BULLETIN No. 189 [June, CABBAGE, Brassica oleracea Atkinson, 4 in 1895, in his article on damping-off diseases, men- tioned cabbage seedlings as being susceptible to damping-off by Rhi- zoctonia. Duggar and Stewart 32 in 1898 received from Illinois specimens of cabbage seedlings which had been diseased by Rhizoctonia. They found that the disease sometimes affected very young seedlings, caus- ing damping-off, but that it was more common after the plants had developed one or two true leaves. In the latter instances, small lesions at or below the surface of the soil characterized the disease. Later, Duggar and Stewart found Rhizoctonia causing a sim- ilar disease of cauliflower seedlings in New York. The plants showed ulcera- tion at the bases of the stems, the entire cortex in some cases having disap- peared. Fawcett 40 reported a stem rot of cabbage seed- lings due to Corticium va- gum B. & C., in Florida, in 1909. According to his description, the disease was a typical stem rot, with a softening of the epi- dermis followed by a shriv- FIG. 10. STEMS OF YOUNG CABBAGE PLANTS INOCU- LATED WITH Rhizoctonia Solani FROM CARNATION FIG. 11. STEM OF AN OLD CABBAGE PLANT WHICH HAD BEEN PLACED IN A BENCH INFECTED WITH Ehizoc- tonia Solani FROM CARNATION (Ex- periment 9) PARASITIC RHIZOCTONJAS IN AMERICA 317 eliiip of the outside tissues and a browning of the leaves. However, the plants so affected did not wilt down entirely, and many of them recovered. CANDYTUFT, Iberis sp. During June, 1914, a few plants of candytuft that had been grow- ing in three-inch pots in the floricultural greenhouses, rotted off at the surface of the ground. The symptoms were similar to those described for sweet alyssum. Microscopic examination of diseased tissue re- vealed R. Solani in every case. Dense masses of hyphse covering the leaves and stems of these plants were plainly visible. Duggar and Stewart 32 in 1901 reported damping-off by Rhizoctonia of cuttings of candytuft in New York. CARNATION, Dianihus caryophyllus Rliizoctonia Solani attacks carnation plants of all ages, both in the field and in the greenhouse, causing not only stem rot, but damping- off of cuttings, of which it is one of the principal causes. The symptoms of stem rot of carnation are very characteristic of the effects of R. Solani (Fig. 1). The fungus usually attacks the stem of the plant at the surface of the ground or occasionally just above or below. As a rule, the first indication of the disease is a pale green color of an entire plant or of a single branch. This lighter color can be noticed in most cases for several days before the actual wilting takes place. During cloudy weather the plant does not wilt for two weeks and sometimes for even longer, altho the stem may be almost completely rotted ; in sunny weather wilting occurs much sooner. If the stem of a plant that shows the first sign of wilting is pressed just at the surface of the soil, a soft place is felt and a slight twist is sufficient to slough off the bark. Beneath this is a slimy, wet area, which gives this rot its characteristic name. Sometimes, however, the stem is dry at the point of attack, and upon being broken off, the fibers appear to be separated and stringy. The fungus enters the cracks in the corky layer of the bark and at- tacks the cambium layer, causing the sloughing off of the bark. It then penetrates the woody tissues, and can be found even in the pith. The plant may remain alive after the cambium layer is destroyed until the fungus plugs the vessels. If a diseased plant is left in the soil for some time, the mycelium overruns the stem, and dark, round sclerotia are formed either directly on the bark or in the crevices, or cracks. The Rhizoctonia disease of carnation has been known to florists ever since carnations have been grown as a commercial crop in the greenhouse. In Volume I of the American Florist, 1886, is found the following paragraph, \vhich is probably the first published statement concerning the stem rot of carnation in this country. " In a few days plants began to show signs of wilting, and upon examination I found them rotted off just at the top of the ground, tho half an inch under the ground the stems appeared perfectly healthy. ' ' 318 BULLETIN NO. 189 [June, 1916] PARASITIC RHIZOCTOXIAS IN AMERICA 319 While the cause of the disease was not known at that time, from the description of the symptoms it is not to be doubted that it was due to Rhizoctonia. A great loss of plants from stem rot occurred thruout the country about 1900. Below are given a few excerpts from notes on this dis- ease which have appeared during the last thirty years, some of which agree with our present-day ideas: 1886. "Deep planting causes the disease in many houses." ' ' In our opinion high temperature and deep planting have much to do with the disease. ' ' 1898. ' ' The most dangerous disease that attacks the carnation. Some varie- ties appear more subject to this disease than others, and there is considerable complaint about Flora Hill and Silver Spray this season. The most common error that very often leads to this disease is too deep planting. The plants should never be planted deeper than they stood in the field, preferably not so deep. The stem of the plant should be out of the ground sufficiently to hold the branches away from the soil. I believe this disease is not found on carnations alone, but on other plants too, and the spores of this fungus may have been embedded in the soiP, carried over or imprisoned, dormant in the plant from the cutting bench. ' ' To check and prevent the spreading of this disease, dust flour of sulfur over the plants, and shake them so it will lodge on the stem and branches and on the soil around the stem. ' ' 1900. "Climatic conditions rather than anything else are the chief causes of the trouble. High ranges of temperature whether in the cutting bench, field, or house, the results are the same, the amount of rot varying with preceding condi- tions. Thus, after heavy rains inducing soft growth, a rise of temperature into the 90 's is a capital condition for the development of stem rot. Some varieties are also more susceptible to attacks than others, the woodier ones being able to withstand it more than those of soft growth. ' ' 1904. ' ' Stem rot is due to allowing plants to become pot-bound. ' ' Rich soil with too much manure causing a rapid growth causes stem rot. I believe this to be responsible for more stem rot than all other conditions com- bined. Too deep planting also favorable for stem rot. Water when absolutely necessary and then water thoroly. ' ' 1906. "Presence of wounds on the bark, or punctures made by insects; faulty planting; sour or too highly enriched soil; lack of drainage; careless cul- tivation; lack of fresh circulating air; the maintenance of too great heat com- bined with atmosphere heavily charged with stagnant moisture during the time when the outdoor stocks are housed, will cause stem rot to become severe in the benches. ' ' 1907. ' ' Stem rot is the most dreaded and only disease of carnations in the South. ' ' 1909. "Stem rot more dreaded in South than in North." 1911. "Fresh air, plenty of circulation, a sweet soil, and proper watering will avoid to a great extent the appearance of stem rot or stop its spread. Weather conditions seem to play an important part, and in most cases as soon as cold nights are the rule, our troubles grow less. The greatest benefit is derived thru a clear and rather dry atmosphere. Deep planting not so important. Too much manure not necessarily a cause of stem rot. "Stem rot is more prevalent in sour soils than others. The surface of the soil should be kept open by frequent scratching. A dry interior and a wet surface is very conducive to stem rot. ' ' 1913. "Stem rot in the South is more serious than in the North." The following older carnation varieties have beeen reported as being especially susceptible to stem rot : La Purite, Crimson King, De Graws, Sewan. Flora Hill, Silver Spray, McGowan, Portias, Scott, Jubilee, 320 BULLETIN No. 189 [June, Craig, Boston Market, Crane, Lawson, Lady Bountiful, Winsor. Sev- eral of these varieties are still propagated by a few growers and with good success, but the majority of them have been discarded. Of the newer types no one seems to be more susceptible than the others. To Duggar and Stewart 30 is owed the discovery that Rhizoctonia is the cause of stem rot of carnation. This they proved conclusively in 1899 by inoculation experiments with pure cultures, repeated many times. Duggar and Stewart state that this stem rot is one of the most troublesome of the carnation diseases and probably occurs thruout the United States wherever the carnation is grown. Stewart 123 ' 124 at the same time distinguished between two distinct diseases, both called ' ' stem rot. ' ' One is caused by Rhizoctonia, and the other by Fusarium. Card and Adams 13 of Rhode Island studied methods of control of both Fusarium and Rhizoctonia rots. They came to the conclusion that the use of clean, fresh sand in the cutting bench helps to control the fungus. They also found that stable manure does not favor, the spread of the disease. In 1902 Stone and Smith 129 reported carnation stem rot in Massa- chusetts. Two years later Clinton 14 reported the presence of the disease in Connecticut. In 1906 Heald 57 stated that it was found in the field and in the greenhouse near Lincoln, Nebraska. Blake and Farley 10 in New Jersey conducted a number of soil experiments for the control of stem rot. CARROT,. Daucus carota Occasionally R. Solani causes damping-off of carrot seedlings, but the plants seem to be more susceptible later, when the fleshy root is formed. Here the rot starts at the crown and works up into the leaf bases. It also progresses into the interior of the fleshy root, as a rule showing no signs on the exterior for some time. In some cases lesions are found on the exterior of the carrot and on the larger secondary roots where they branch from the fleshy part. Duggar and Stewart 32 were the first to find a disease of carrot due to Rhizoctonia. In 1911 Heald and Wolf 59 reported from Texas the Corticium stage of the fungus on carrot. They stated that the roots were covered by white, ropy strands of the fungus, but that no serious rotting was observed. CELERY, Apium graveolens A damping-off of celery seedlings in flats by RMzoctonia Solani has been observed in the Station vegetable-gardening greenhouses. The symptoms are similar to those described for beets. During a search in the market in the winter of 1914 for leaf spot and soft rot on celery, several bunches shipped from New York were 1916] PARASITIC BHIZOCTONIAS IN AMERICA 321 found to have a brown mycelium and many small sclerotia between the stalks near the base. The fungus was causing no injury to the celery. When examined in the laboratory, the mycelium and sclerotia proved to be those of Rhizoctonia. Pure cultures of the fungus were obtained readily from the sclerotia. Repeated examinations of new shipments of celery from New York showed that in the majority of cases Rhizoc- tonia was present between the stalks. Duggar and Stewart 32 in 1901 were the first to report Rhizoctonia causing a destructive damping-off of celery seedlings. Rolfs 95 in 1905 reported a damping-off of seedlings in Florida caused by Corticium vagum B. & C. Van Hook 136 found a Rhizoctonia associated with a root rot of celery in the field. He did not believe, however, that this fungus was the cause of all the trouble. Affected plants never attained full size, and an examination of the roots showed considerable decay. The disease seemed to affect the main roots, which rotted off rapidly near the crown. The fact that seed beds in new soil did not entirely control the trouble showed that the fungus Rhizoctonia was present in the new soil, tho not in any great amounts. Halligan, 51 in Michigan, has also studied the damping-off of celery plants in the seed bed. Centaurea gymnocarpa In the spring of 1914 a large number of seedlings of Centaurea gymnocarpa, including some of those which were potted, damped off. By June many of the potted plants were dying with stem rot, the dis- ease having been carried over on affected seedlings and in a few cases, no doubt, on healthy ones. Microscopic examination and pure cultures showed that in each case R. Solani was present in the diseased tissues. The progress of the disease was rather typical. The first symptom was the wilting and drying up of the foliage. On pulling up the plant, a number of the leaves were seen to be rotted off at the crown, while the bark on the stem below the surface of the ground sloughed off and the tissues beneath were wet and stringy. CLOVER, RED, Trifolium pratense In the spring of 1914 damping-off of red and Japanese clover was observed in the agronomy greenhouses. A culture easily obtained from the fungus appeared to be the same in all respects as the one isolated from alfalfa seedlings which were growing under similar con- ditions in close proximity. Stevens and Wilson 122 in 1911 reported that in a field of clover in North Carolina the roots were being attacked by Rhizoctonia and were suffering some damage. This is the only instance in which Rhizoctonia has been reported as injuring clover in the field. 322 BULLETIN No. 189 [June, COLEUS, Coleus sp. In November, 1912, cuttings of coleus began to damp off in a bench in the floricultural greenhouses. The variegated green varieties seemed more susceptible to the fungus than the variegated red and yellow. The trouble was found to be due to R. Solani. The infected cuttings showed characteristic lesions on the stems at the surface of the sand. These lesions were quite large and distinct, brown in color, and depressed several millimeters at the center. They were generally found on one side, but in some cases the whole cutting was girdled. Practically all the coleus cuttings in the bench damped off in this manner. During October, 1913, Ehizoctonia was found causing a damping- off of coleus seedlings planted very close in flats. About half the plants damped off. Duggar and Stewart 32 reported a damping-off of coleus cuttings in New York, caused by Rhizoctonia, similar to that observed at this Station. CONIFEROUS SEEDLINGS The first case reported of damping-off of white-pine seedlings due to Rhizoctonia was by Duggar and Stewart, 32 from New York. Ten years later Clinton 1 7 mentioned the damping-off of a number of conif- erous seedlings. Hartley, 55 who made a study of the damping-off of coniferous seed- lings in the West, found that Rhizoctonia is one of several organisms involved. He wrote as follows : "Ehizoctonia (probably Corticium vagum B. & C.), which causes dumping-off of very young seedlings, sometimes continues to work in patches till the plants are two months old or even more. On sandy soil, when seedlings from five to nine weeks old are killed, the youngest and deepest parts of the roots are usually first attacked. At Halsey, roots of Eocky Mountain yellow-pine seedlings about seven weeks old have been attacked at points as much as eleven inches below the ground surface. In many plants as old as this the older parts of the roots resist the en- trance of the fungus which has rotted the younger parts and throw out new root branches, so that recovery takes place without any evidence of the damage being shown by the plant above ground. ' ' Coreopsis lanceolata Duggar and Stewart 32 in 1901 mentioned the fact that next to a plot of sweet williams that were being killed by Rhizoctonia, were two rows of Coreopsis lanceolata which were also diseased. They stated that "only a few plants were killed, but from many of them the lower leaves had rotted away. The rot seemed to start in the base of the petiole, where it came in contact with the soil. The decaying leaves were overrun with Rhizoctonia." 1'AKAsiTK' BHIZOCTOMIAS IN AMERICA 323 CORN,' Zea mays In 1914, during the progress of the soil survey for R. Solani, the fungus was found frequently on corn roots in the field. It could not be determined whether the fungus penetrated the roots or not, but there was no question as to the abundance of the mycelium on the roots. Rolfs 05 in 1905 reported Corticium vagum B. & C. on corn in Florida. COTTON, Gossypium herbacsum Grlover 40 in 1855 described a respects is the same as the disease FIG. 13. STEMS OF YOUNG CARNA- TION PLANTS INOCULATED WITH EHIZOCTONIA FROM COTTON, SHOWING LESIONS CHARACTERIS- TIC OF SORE SHIN OF COTTON CAUSED BY THE SAME FUNGUS sore shin of cotton, which in some of seedling cotton caused by Rhizoc- tonia. He stated that ' ' the cause is attributed by many to cold, cutting winds, when the plant is very young. Others, however, assert that when a high wind shakes a tender plant, the main stem is so much bent and twisted that the sap ves- sels are upturned and a serious in- jury occurs." One of the causes of sore-shin disease of cotton remained undis- covered until Atkinson, 5 in 1896, found in the diseased tissues a ster- ile mycelium, which he later identi- fied as Rhizoctonia. By means of pure-culture methods and inocula- tion experiments he further proved that this sterile fungus was the cause of sore shin and also of seed- ling rot and damping-off of cotton. He describes the Rhizoctonia dis- ease of cotton as follows : ' ' There are several phases of the disease. Sometimes the tissues undergo a soft rot which progresses very rapidly, and the early stages are not marked by any striking color characteristics. Another phase may progress rapidly or slowly and is usually quite well characterized by a reddish brown color which accompanies it. This phase is also characteristic in that it is usually manifested on one side of the stem in the form of an ulcer which gradually deepens until the vascular sys- tem is reached, when the life of the plant becomes really endangered. Even when this stage is reached, however, the plant may, and does frequently, recover. "This latter phase is characteristic of a very common disease of seedling cotton. It is called by the planters in many places ' sore shin. ' "The diseased portion of the plant is just beneath the surface of the ground and presents an area of shrunken tissue of a dull brown or reddish color. The 324 BULLETIN No. 189 [June, size of the shrunken area and the depth of the injury are proportionate to the serious condition of the ulcer, as it may be termed. If the injury remains con- fined to the superficial tissues, the plant will usually recover. It does sometimes recover when the injury reaches the vascular tissue, but more frequently death results when the trouble has progressed thus far. ' ' No further original work has been done on this disease since the time of Atkinson, altho several of the southern experiment stations have published bulletins on cotton diseases, including the sore shin and seedling rot due to Rhizoctonia. DiantJius R. Solani was isolated from diseased plants of DiantJius barbatus (Newport Pink), during July, 1913, in the perennial garden of the Station. This variety and DiawtJius barbatus (single mixed) were much more susceptible to stem rot than were any of the other varieties grown. In fact, practically every plant of these two varieties died from stem rot during the summer. These varieties are more like the carnation than any of the others, and when affected, the symptoms of the disease were very similar to those of stem rot of carnation. The first evidence of the disease was the pale green color of the leaves, followed in many cases by a sudden wilting of the foliage. When plants in this stage were pulled up, the bark readily sloughed off, leaving the wood exposed. When plants in the later stages of the disease were pulled up, the stem usually broke off at the surface of the ground, exposing stringy tissue. During the same month, a disease of DiantJius sequeri and D. plumarius was under observation. Diseased parts of these plants yielded Rhizoctonia in every instance. In the case of D. sequeri the fungus seemed to be living saprophytically among the numerous pros- trate, bushy branches. The brown strands of the mycelium could be plainly seen running thru the bushy mass of the plant. Only a few plants died. Unlike the case of D. barbatus, there was no characteris- tic sloughing off of the bark, but a more or less general rotting of the whole stem, which left the tissues very dry and stringy. The attack was not confined to the main stem, but affected any of the branches which touched the ground. Most of the plants of D. plumarius, occupying a space about three feet long, died from attacks of the fungus. The symptoms of the dis- ease were very similar to those of D. sequeri, the rotting appearing to extend gradually from one point thru the whole stem. As with D. sequeri also, the bushy habit of the plant gave ample protection to the fungus, and the radiating strands of the brown mycelium of Rhizoc- tonia were visible to the naked eye. Duggar and Stewart 32 in 1900 found a badly diseased plot of DiantJius barbatus in which 90 percent of the plants, in the course of the season, died from stem rot due to Rhizoctonia. 1916] PARASITIC RHIZOCTONIAS IN AMERICA 325 EGGPLANT, Solatium melongena During August, 1912, while some field observations were being made on carnation stem rot, the fruits of a number of eggplants in an adjoining field were found to be rotting at the point where they touched the ground. The decay spread in all directions from this point, making a sunken, brown area ; this was followed by the soften- ing and subsequent collapse of the surrounding tissues. Fruits showing this decay were brought into the laboratory and placed under a bell jar. Around the diseased spot there soon developed a thick mass of mycelium, which on microscopic observation was found to consist of hyphse of Fusarium and Rhizoctonia. The decaying spots contained no fungous threads, but were completely filled with bacteria. On plat- ing, pure cultures of R. Solani were obtained. The cause of the pri- mary infection is not known. It is very probable that both the Fusar- ium and Rhizoctonia entered the tissues where the epidermis had been destroyed. In July, 1913, the damping-off of a number of eggplant seedlings in the vegetable greenhouses was noticed. This was shown, by pure cultures of the diseased material, to be due entirely to Rhizoctonia. The fungus produced the characteristic lesions on one side of the seed- lings at the surface of the soil, causing the stem to break. Atkinson, 4 in his account of damping-off diseases, mentioned eggplant seedlings among those susceptible to attacks of the sterile fungus (Rhizoctonia). Rolfs 95 reported the presence of the Corticium stage of Rhizoctonia on mature plants in an irrigated garden. Here the plants affected drooped for a time and then wilted and died. Le- sions were formed on the stems at the surface of the ground. Wolf 140 ' 141 in 1914 reported damping-off and a fruit rot of eggplants due to Rhizoctonia (Corticium vagum B. & C.), but he does not re- gard the fungus as the cause of serious injury to eggplants. FIVE-FINGER, Potentilla sp. A number of five-finger plants were found to be infected with R. Solani during June, 1914, in inoculated sections in the floricul- tural greenhouses. The mycelium of the fungus was present at the nodes which touched the soil and also at the bases of the plants, where crown rot was developing. FOXTAIL GRASS, Setaria glauca Several plants of foxtail grass growing under the same conditions as the preceding host, five-finger, showed a root infection. GypsopMla repens A number of Gypsophila repens plants were found diseased in the herbaceous grounds during July, 1913. Pure cultures of the diseased 326 BULLETIN No. 189 [June, material showed the causal organism to be R. Solani. The plants were bushy, so that some of the branches and leaves were in contact with the soil. The symptoms and appearance of the disease were similar to those described for Dianthus. LAMB'S QUARTERS, Clienopodium album During the summer of 1913 several wilted Clienopodium plants were observed along the border of the old herbaceous grounds of the Station. On pulling up the wilted plants, it was found that R. Solani was the cause of the wilting. The fungus did not enter very deep into the tissues, but rather girdled the stem and formed a scurfy layer. Duggar and Stewart 32 in. 1901 reported the occurrence of Rhizoc- tonia on Clienopodium album. Lavatera arborea variegata During March, 1913, in the floricultural greenhouses, a number of seedlings in small seed pans, among which were several pans of Lava- tera, began to damp off in a manner characteristic of R. Solani. Pure cultures of diseased seedlings yielded this fungus. Strands of the brown mycelium could be seen on the surface of the soil and extending up on the stems and leaves. This was noticed again in the spring of 1914. LETTUCE, Lactuca sativa Atkinson 4 in 1895 mentioned the damping-off of seedling lettuce, among a number of other plants, by a sterile mycelium which later proved to be Rhizoctonia. Stone and Smith 128 found that R. Solani caused a rot of green- house lettuce, altho the disease was not common. The first appearance was on the lower leaves where they lay on the ground ; a brown rot set in, which spread thru the leaf in a very characteristic manner. The green blade rapidly rotted away, leaving the midrib and stalk as sound as tho the blade had been carefully cut away or had been eaten by insects. Duggar and Stewart 32 observed the damping-off of lettuce seed- lings by Rhizoctonia for a number of years. They found that at or near the surface of the ground the tissues become water-soaked in appearance and unable longer to support the seedling, so that it falls to the ground, the fungus invading all parts. Within a day or two this fungus, under favorable conditions, wilted do\vn and destroyed whole boxes of lettuce seedlings. Duggar and Stewart also observed several times what was apparently the same fungus causing a disease of mature lettuce plants. On the older leaves the leaf blades alone were affected, but the more delicate inner leaves succumbed entirely, blackening and decaying with the progress of the disease. 1916] PARASITIC KHIZOCTONTAS IN AMERICA 327 Iii 1903 Selby 104 reported the presence of a rosette disease of let- tuce, which he described as follows: "The plants affected showed, usually not long after transplanting, but occasionally at other stages, a failure to send out central leaves freely. The leaf-bearing axis re- mained shortened, and the last leaves formed remained short, making a very striking contrast to the remainder of the plants in the bed and to the lower leaves of the same plant. (Frequently the plants overcome this tendency and make a fair amount of product with longer time.) Examination of the roots showed areas occupied by the hyphae of Rhizoctonia. " In 1906 Selby 106 treated at length the control of rosette in lettuce due to Rhizoctonia. Fio. 14. DAMPINO-OFF OF LAVATERA SEEDLINGS BY Bhizoctonia Soldni (Experiment 9) 328 BULLETIN No. 189 [June, In 1905 Rolfs 05 reported the presence of the perfect stage, Cor- ticium vagum B. & C., on lettuce from Florida. Lobelia erinus (Single Blue) The lobelia plants in the floricultural greenhouses in 1914 were small and sessile, and covered the tops of the pots in which they were growing. In June a number of them began to die. On close exami- nation, strands of R. Solani could be seen spreading thru the mass of plant material. The low-lying leaves afforded a good hiding place for sow bugs, and no doubt they helped in carrying the fungus from one pot to another. Attacks of Rhizoctonia on other varieties of lobelia have been observed in the greenhouses a number of times. ONION, Allium sp. A culture of Rhizoctonia isolated from onion seedlings was ob- tained from Cornell University by Mr. H. W. Anderson in 1911. Since that time the author has worked with this strain both in the laboratory and in the greenhouse. From its morphological and physiological behavior, it must be classed as distinct from the other strains. Dr. I. C. Jagger states in a letter that he first isolated this form from onion on May 29, 1911, from seedlings growing on muck soil in New York. He found that the Rhizoctonia mycelium was always con- fined to the first, or seed, leaf and that damping-off ceased as soon as the second leaves had developed. PANSY, Viola tricolor During the fall of 1913 pansy plants were placed in a solid bed, in the floricultural greenhouse, as a border for sweet peas. At that time some of the sweet-pea plants died, and eventually a culture of R. Solani was obtained from them. The following April several pansy plants in the vicinity of the spot where the sweet peas had died became diseased and later died. A culture showed the trouble to be due to Rhizoctonia. Later a large number of the plants in the row died. The fungus attacked the plant at the crown and caused a rapid rot. The prostrate branches, the petioles of the leaves, and even the leaves them- selves were also rotted in a characteristic fashion. The strands of the mycelium could easily be seen ramifying between the rotting mass arid the soil. PLANTAIN, Plantago aristata Diseased plants of plantain were found during June, 1914, in inoculated sections in one of the floricultural greenhouses. The mycelium of R. Solani was present around the bulbous base of the 1916] PARASITIC EHIZOCTONIAS IN AMERICA 329 plants, causing a crown rot. In one or two cases several leaves were completely rotted at the crown. POINSETTIA, Euphorbia pulcherrima About October 7, 1912, young poinsettia plants were taken from the cold house (50 to 60 C.) of the flori cultural greenhouses and put in a box with a glass top. They were then placed near the cutting bench, in which a number of plants of various kinds were damping off. The poinsettia cuttings shortly afterwards began to die off rapidly. The characteristic lesions on the stems of the young plants and pure cultures of the diseased material indicated that this condition was due to R. Solani. The lesions, instead of being on one side and more or less localized, in almost every case formed a collar around the stem at the surface of the soil. The collar was about 2 to 3 millimeters wide, somewhat depressed, and of a dark color. Strands of the brown mycelium were visible spreading over the soil in the pots. This infec- tion probably had its origin in the cutting bench. POTATO, Solanum tuberosum On the potato R. Solani exhibits a number of interesting charac- teristics, which vary with climatic conditions, age of the host, and part of the plant attacked. The sclerotial stage of this fungus has been observed on practically every Illinois potato tuber examined by the writer. Moreover, in every shipment from other states which has been examined, the fun- gus has been found present. The tubers affected were dotted with brownish black sclerotia of various shapes and sizes (Fig. 15), but so far as could be determined, they were causing no direct injury. This type of Rhizoctonia disease of potato is the one most commonly found in the United States. R. Solani also causes, under certain conditions, a russeting, or scab, a cracking of the tuber, the formation of pits at or near the len- ticels, and a wet rot of the tuber. These types of injury have been ob- served by Rolfs 92 ' 93 in Colorado, by Orton 73 in various states, and by Morse and Shapovalov 69 in Maine. On the plant itself this fungus produces various types of diseases. In many cases young plants are completely cut off before they reach the surface of the ground. Older plants that are severely attacked just below the surface of the ground usually die off quickly. If they are only slightly attacked, the fungus produces small lesions on the stems, the plants take on a dwarfed and unhealthy appearance, and the tubers remain small, altho the plants usually live thru the sum- mer. When the stem is girdled by the fungus so as to prevent trans- location entirely, large tops are produced, aerial tubers are formed, 330 BULLETIN No. 1SU FIG. 15. POTATO TUBER SHOWING THE SCLERGTIA. OF Rhizoctonia Solani J.016] PARASITIC EUIZIHTONJAS IN AMKKICA 331 and in some cases a curling of the leaves or resetting results. When the main stein is attacked below the surface of the soil and the stolons are cut off, the condition known as "little potatoes" is produced; in such cases a cluster of small, short-stemmed tubers is formed above the wound. The production of aerial potatoes, rosette, and leaf curl- ing also occurs when the stolons are attacked and the young tubers arc cut off. These abnormal developments of the potato are usually associated, and are secondary physiological effects due to disturbances of the nutrition of the plant. They occur most frequently on poorly drained land and especially on heavy soils. Rolfs 92 attributed the potato failure of 1902-03 in Colorado to little potato. Selby 103 in Ohio, in his studies of the Rhizoctonia dis- ease on potato, gave particular attention to rosette. In 1914 Morse and Shapovalov 09 concluded that the Rhizoctonia disease of potato is of a more serious nature than is generally considered. In one field which they had under observation for several seasons, they attributed the poor and uneven stands, unexpected low yields, early ripening, and death of the tops to Rhizoctonia. In most cases they confirmed the observations made by Rolfs. Recently investigators all over the country have been emphasizing the serious nature of the disease. In January, 1915, material of Rhizoctonia Crocorum on potato tubers was received from Mr. F. D. Bailey of the Oregon Agricultural Experiment Station. On comparing it with Rhizoctonia Solani, it was found to be entirely different in all respects. However, this fungus is identical with the fungus on alfalfa reported by a number of observers (Webber, Heald, and Freeman) as R. Crocorum. Thus it appears that R. Crocorum is present in this country on alfalfa and on potato tubers. Bailey 8 describes the Rhizoctonia disease of potato as follows : ' ' The surface was almost entirely covered with a dense, felt-like mat of a chocolate color when dry, violet -brown when moist. This mat was found to be composed of mycelium which had long narrow cells and a branching habit char- acteristic of Rhizoctonia. The greater part of this mycelial mat could be easily removed, and beneath this the surface of the tuber was covered with very small dark spots. These spots appeared to the unaided eye as minute eruptions of the skin. Under the microscope one can see the mycelial threads attached at these points, and a freehand section thru such a spot shows it to be a structure com- posed entirely of interwoven fungus threads forming a sclerotium. No evidence of differentiation or any type of spore formation within this body could be found on examination of many sections. The portion of the sclerotium near the sur- face is composed of cells that are very deeply colored, giving the black appear- ance. The outer surface of the sclerotium is seen to project above the surface, while the lower or underlying portion is embedded in the outer cortical layers of cells of the tuber. Furthermore, there is a strand of fungus tissue extending deeper than the sclerotium, which connects it with a layer of the same type of fungus tissue spreading between the cortex and parenchyma from the poini where this strand reaches the parenchyma. "Attempts to grow this fungus in culture failed. This has been the experience reported in attempts to grow Khisoctonia violacea Tul. " 332 BULLETIN No. 189 RADISH, Eaphanus sativus [June, Damping-off of radish seedlings by R. Solani has appeared sev- eral times in the floricultural greenhouses. During May, 1914, an at- tack of Rhizoctonia on mature radishes was observed in the writer's home garden. The first sign of the disease was the yellowing of the foliage, followed by the wilting of the leaves. On pulling up a plant, the crown was found to be rotted at the base of the leaves. The rot progressed slowly and killed only a few of the plants. After it had proceeded for some length, the radishes cracked farther down. This is very characteristic of the disease at this stage (Fig. 16). In 1895 the damping-off of radish seedlings by a sterile fungus, which was later identified as Rhizoctonia, was first reported by Atkin- son. 4 Duggar and Stewart 32 in 1901 noted a disease caused by Rhi- zoctonia of mature radishes forced in a greenhouse. The disease caused a soft rot of the crown or lesions in this region. The leaves were generally unaffected until a large part of the root had decayed. Plants in all stages of growth were affected and killed. Duggar and Stewart also found a Rhizoctonia in connection with the damping-off of radish seedlings in the greenhouse. FIG. 16. LATE STAGE OF ROOT EOT OF RADISHES CAUSED BY Rhizoctonia Solani 1916] PARASITIC RHIZOOTOXTAS IN AMERICA 333 In 1904 Clinton 14 observed a damping-off and root rot of radish due to Rhizoctonia. Apparently the disease was not very serious. Stewart 125 in 1910 also reported a damping-off and root rot of radish due to Ehizoctonia. Infection took place first at the level of the soil, causing the leaves to have a wilted, drooping appearance. From this point the disease spread into the leaves and roots of the plant, soon causing death. On mature radishes, decayed spots of irregular shape were produced, and at an advanced stage the diseased portions of the plant were covered with a white, felted mycelium. RHUBARB, Rheum rhaponticum In 1901 Duggar and Stewart 32 reported a disease of rhubarb, on Long Island, which they had had under observation for several years. They described the disease as follows : ' ' An unthrifty condition of the plants was noticed, followed by the rapid dying off of many of the leaves. The affected leaves became dry and shrunken in appearance and soon fell to the ground. Where a field was badly affected, the majority of hills showed the trouble to the extent of at least a leaf or two. In several instances from one-fourth to three-fourths of the leaves were already dead. An affected leaf breaks off readily just beneath the surface of the ground, and old dead leaves rotted off in this region. The general appearance reminded one strongly of the effect of Rhizoctonia upon beets. There was very little super- ficial mycelium visible to the unaided eye. Microscopic examination showed hyphse of a Rhizoctonia both superficially and immediately under the surface where the leaves were rotting." Clinton 14 has also reported a stem rot of rhubarb due to Rhizoc- tonia. He found the fungus at the base of leaf petioles, causing dark, sunken cankers. SALVIA, Salvia splendens The symptoms of the Rhizoctonia disease of salvia observed in the flori cultural greenhouses were similar to those described for coleus. All varieties of the cuttings in the bench seemed to be equally suscep- tible. It has been shown that the serious damping-off of the salvia, al- ternanthera, and coleus was due to the fungus which was first brought in on the mature alternanthera plants from which cuttings were made. (See Alternanthera, page 310.) Santolina chamcecyparissus In 1914 a number of plants of Santolina chamcecyparissus growing in pots next to the Centaurea gymnocarpa in the floricultural green- houses, were found to have a typical stem rot, due to R. Solani, very similar to the disease as described for that plant (see page 321). The fungus could be distinctly seen running thru the bushy branches. 334 BULLETIN No. 189 [June, Sedum sp. A few plants of Sedum anglicum, together with several other spe- cies of Sedum, were found diseased, in July, 1913, in the herbaceous grounds. The progress of the disease was very slow ; few plants were killed during the entire summer. For the most part, the fungus seemed to live saprophytically at the base of the plant. It was also found on healthy plants of this genus.. About six species were planted in a row in the garden, and all were affected in much the same way. SORREL, Rumex acetosella In June, 1914, a number of sorrel plants were found diseased in an inoculated section in the greenhouse. The stems of the plants were covered with the brown strands of mycelium, and a few of the leaves were rotted off at the crown. Pure cultures of the diseased parts yielded R. Solani in every case. During July, 1912, when the young sweet peas in the field were about one-third to one-half grown, occasional vines showed evidence of disease by turning yellowish, wilting, and finally drying up en- tirely. An examination of the affected plants showed that they were more or less separated from their roots near the surface of the ground. Pure cultures of the diseased material yielded R. Solani in all cases. In November, 1913, several diseased seedlings were brought in from the plant-breeding greenhouses. On close examination the stems showed the characteristic lesions caused by Rhizoctonia. The same trouble occurred in the floricultural greenhouses the past two seasons, but in no case was it severe. During the winter of 1913, the writer was called to Chicago to look over a range of greenhouses devoted to the growing of sweet peas. Sweet-pea plants of all ages were seriously affected. Dead plants were scattered thru the whole house. Close examination of the diseased plants revealed the fact that Rhizoctonia was causing the trouble. Apparently it started in the seed pans and continued to work until the plants were ready to be discarded. The symptoms in each case were the same yellowing of the foliage, followed by the wilting and dry- ing up of the plants. Characteristic lesions, which finally cut the stems off at the surface of the soil, could always be found on the dis- eased plants. The root systems were much dwarfed. In 1908 Clinton 16 observed in Connecticut a damping-off of sweet peas due to Rhizoctonia. Taubenhaus 130 ' 131 in describing a Rhizoc- tonia rot of sweet pea at different stages, states that he found it quite destructive to the plants when they are in the seedling stage. I'AHA.SITIC RimCKTOXlAS IX AMERICA 335 TOBACCO, Nicotiana sp. In 1904 Clinton 14 noticed a seed-bed rot of tobacco, which he thought was due to Rhizoctonia. The same year Selby 105 observed a similar bed rot of tobacco in Ohio caused by Rhizoctonia. He stated that the specific characteristics of the fungus do not differ essentially from those of its forms on other plants, including potato. Clinton, 15 in making another report on this disease, in 1906, stated that the injury to the plants was slight and was confined, as with the potato, to the underground parts. Johnson 63 has carried on some extensive work on Rhizoctonia, with a view to controlling the damping-off of tobacco seedling^. TOMATO, Lycopersicum esculentum A damping-off disease of tomatoes caused by Rhizoctonia has been noted from a number of states; the symptoms of the disease are the same as have been described for a number of other plants, such as eggplant. In connection with his w r ork 011 the potato rosette resulting from Rhizoctonia, Selby 104 also mentioned a tomato rosette caused by the same fungus. He stated that the tips of diseased plants showed rather long internodes and dwarfed leaves, with somewhat curled-leaf aspects, while the roots had lesions and other similar features found in potato rosette. . Rolfs 95 in 1905 stated that he frequently found the Corticium stage on the tomato plant, but that apparently the plants do not suffer ma- terially from its presence when planted on well-aerated land. He described it as follows : "The fruiting stage of the fungus develops freely on the stem just above the surface of the ground, often extending up the stem for a distance of six inches. As a rule the fungus does not penetrate the tissue here, but simply covers the stem of the plant. The tomatoes which touch the ground are frequently more or less covered by a fruiting membrane of the fungus, which mars the appearance of the ripe fruit. So long as the tomatoes are green and the skin uninjured, the fruit remains sound ; however, if the skin is ruptured, the fungus soon destroys it, pro- ducing a brown rot. This organism also frequently gains entrance to the fruit at the stem end." Orton 72 described the rosette of tomato caused by Corticium vagum B. & C. as a disease of minor importance in tomato culture. He stated that ' ' the fungus attacks the roots and base of the stem, forming dark cankers. The effect on the plant is to dwarf and curl the leaves and to restrict productiveness." A fruit rot of the tomato has also been observed by Pool 86 and again by Wolf. 141 Pool described the symptoms of the fruit rot as follows : ' ' The specimen examined showed no rupture in the external skin visible to the naked eye. The diseased area was plainly distinguishable by the chocolate- 336 BULLETIN No. 189 [June, colored, slightly wrinkled epidermis. An examination of the underlying tissues revealed the same general color and numerous, somewhat darkened filaments pene- trating the cells in all directions." Wollenweber 1 42 in 1913 described a species, Rhizoctonia poto- macensis Wr., which causes a fruit rot of green tomatoes. He stated that this species differs from Rhizoctonia Solani in the character of its attacks, in that concentric, subepidermal mycelial zones are formed within the tomatoes. VIOLET, Viola odorata During ^he fall of 1913 a number of violet plants in the floricul- tural greenhouses were found to be diseased. A few had stem rot, while on others only the bases of the petioles were somewhat rotted. Where the pots were set close together and the plants overlapped, the brown strands of R. Solani could be plainly seen spreading out from one plant to another. However, in no case was the disease severe ; it is probable that the fungus was living saprophytically on the lower leaves. Duggar and Stewart 32 observed, in a greenhouse in New York, one case of destructive violet stem rot due to Rhizoctonia and a second case similar to the attack described above. ADDITIONAL OBSERVATIONS Beside the hosts that have been mentioned, observations have been made in the floricultural greenhouses of diseased seedlings and cut- tings of a number of other plants, tho no work has been done further than to make a microscopic examination of the diseased material. Below is a list of seedlings and cuttings found damping off in the spring and fall of 1914, with the percentage of loss resulting. In all cases Rhizoctonia proved to be the cause of the trouble. Percentage Seedlings Damping off, April 6, 1914 of loss Amaranthus caudatus 75 salicifolius 90 Bartonia aurea 90 Calendula Pongei 1-2 Celosia Huttoni, var. Thompsonii magnifica 75 Chrysanthemum hortorum 30-40 Dianthus chinensis 80 Heddewigii 30 latifolius 80 Godetia sp 80 Gypsophila muralis 30 Kochia trichophylla 99 Lavatera arborea variegata 5 Linaria Maroccana 5 Linum grandiflorum rubrum 30 Lychnis coeli rosa 90 Portulaca oleracea 80 Schisanthus sp 2-4 1916] PARASITIC EHIZOCTONIAS IN AMERICA 337 Percentage Seedlings Damping off, September 2, 1914 of loss Aqullegia (6 species) 85 Campanula (8 species) 80 Cineraria (several species) 20 Dianthus plumarius 85 Erysimum pulchellum 2 Linaria Cyinbalaria 2 Lythrum sp 2 Matthiola incana (stocks) 2 Primula malacoides 2 ' ' obconica grandiflora 2 Schizanthus (mixed) 2 Kilene Schafta 100 Stachys lanata 2 Viola tricolor (3 varieties) 20 Cuttings Damping off, September 25, 1914 Abutilon hybridv/m, var. Savitzii 100 Acalypha Wilkesiana, var. bicolor 100 tricolor 100 " " marginata 90 Ageratum mexicanum vars 2 Alyssum odoratum (3 varieties) 100 Coleus (10 varieties) 2 Cuphea platycentra 2 Iresine (Achyranthes) (5 varieties) 95 Petunia (several varieties) 100 Piqueria trinervia (Stevia) 100 Santolina chamcecyparissus 2 Sedum spectabile 2 Telanthera (Alternanthera) (9 varieties) 2 Vinca major (several varieties) 2 TYPES OF SYMPTOMS From a study of the symptoms caused by Rhizoctonia Solani on the various hosts, it is seen that, except for a few minor points, they are the same when appearing on the same type of host. The damping- off of seedlings and cuttings of various plants is identical, as is the rotting of a number of root crops. In most herbaceous plants a stem rot is produced, the symptoms of which are also identical on the vari- ous hosts. On very resistant plants lesions only are formed ; these are apparently identical on the different hosts. INOCULATION EXPERIMENTS The main purpose of these inoculation experiments was to ascer- tain the degree of biologic specialization which may exist between the various cultural strains of Rhizoctonia, or between strains isolated from different hosts or of different geographical origin. With three thousand square feet of glass available in the floricultural greenhouses and with the assistance of the members of the floricultural division, it was possible to carry on cross-inoculation experiments involving about 338 BULLETIN No. 189 [June, 3,000 cuttings, 2,000 plants, and 7,000 seedlings of various kinds. With these, comparisons were made of about forty-five strains of Rhizoctonia. A large number of the strains used in these experiments were iso- lated by the writer from the various hosts found infected with Rhizoc- tonia in this vicinity. Other strains were obtained from various in- vestigators thruout the country. Below is presented a list of the strains used and the source of each. Alfalfa. A Rhizoctonia culture from alfalfa was received from Dr. C. W. Edgerton, Baton Rouge, Louisiana, November 12, 1912. It was originally ob- tained by Dr. Edgerton in May, 1910, from alfalfa seedlings. Alternanthera B.A.C. -A. culture of Rhizoctonia was isolated from infected alternanthera cuttings found in the floricultural greenhouses in the fall of 1912. Alternanthera R.A.F. This strain was obtained at the same time as the preceding, from mature alternanthera plants in the field. Amaranthus. In August, 1913, Mr. W. H. Burkholder, of Cornell University, contributed several specimens of AinarantTws retroflexus infected with Rhizoc- tonia, from Irving, New York. The stems were covered with the immature, gray, felt-like mycelium of the Corticium stage. Scrapings of the hymenial layer of this stage yielded pure cultures of Rhizoctonia in every case. Aster. Early in 1913, Dr. F. A. Wolf sent to the writer a culture of Rhizoc- tonia which was the cause of the damping-off of China aster seedlings in flats in the greenhouse at Auburn, Alabama. Bean. A transfer of a culture of Rhizoctonia from bean was obtained in December, 1912, from Dr. J. T. Barrett, of this university. He in turn had re- ceived it from Dr. M. F. Barrus, of Cornell University, about 1910. Beet. A culture of Rhizoctonia was obtained from young seedlings of the garden beet found damping off in the vegetable-gardening greenhouses, July 10. 1913. Begonia. The strain from begonia was isolated by Mr. Anderson from cut- tings found damping off in the floricultural greenhouses in the fall of 1911. Carnation. During the season of 1911-12, Mr. Anderson isolated Rhizoctonia from a number of carnation plants received from different sources, and during 1912-13 and 1913-14 the work was continued by the author, so that a comparison of a large number of cultures from diseased plants obtained from various localities was possible. The strains used are given below. "Carnation R.K. ": Isolated by Mr. Anderson from diseased carnation plants obtained at Urbana, Illinois, in October, 1911. "Carnation R.O. ": Culture isolated by Mr. Anderson in the fall of 1911, at Urbana. "Carnation R.H. ": Culture isolated from a diseased plant in the floricul- tural greenhouses in the fall of 1911 by Mr. Anderson. "Carnation R.S. ": Isolated from diseased plants received from Kankakee, Illinois, by Mr. Anderson, October 25, 1911. "Carnation R. 2": Culture reisolated by Mr. Anderson from infected cut- tings in sterilized soil in the spring of 1912. "Carnation R.F. ": Isolated from diseased carnation plants gathered in the field in the horticultural grounds, July 24, 1912. "Carnation R.M.2": Isolated from a White Enchantress plant in one of the floricultural greenhouses during September, 1912. ' ' Carnation R. 107 ' ' : Obtained from a plant in the floricultural greenhouses, September 7, 1912. "Carnation R.F.2": Culture obtained from a diseased plant in the field during the summer of 1913. "Carnation R. 121-5": A reisolation of Rhizoctonia was obtained on De- cember 3, 1912, from a diseased plant in one of the inoculated sections of tho greenhouse. Carrot. The strain of Rhizoctonia from carrot used in this work was ob- tained by Mr. Anderson from Cornell University in 1911. Nothing is known of the origin of the culture. 1916] PARASITIC RHIZOCTONIAS ix AMERICA 339 Cauliflower. A culture of Rhizoetonia from cauliflower was obtained in 1912, from Dr. C. W. Edgerton, Baton Bouge, Louisiana. This culture was isolated from diseased cauliflower seedlings in the summer of 1912, so that it was a comparatively fresh culture when received here. Clienopodium. A culture was isolated during the summer of 1913 from ma- ture plants of Chenopodium album growing along the border of the old herbaceous grounds back of the floricultur,al greenhouses. Clover. A culture of Rhizoctonia from red-clover roots was received from Mr. E. A. Arzberger, Wooster, Ohio, March 3, 1913. The fungus was isolated by him from red-clover roots in the greenhouse in December, 1912. Coleus I. This strain was obtained from coleus cuttings found damping off in the floricultural greenhouses, November, 1912. Coleus II. A culture was isolated from coleus seedlings damping off in seed pans, October, 1913, in the floricultural greenhouses. Corn. The strain from corn was obtained from Dr. J. J. Taubenhaus, New- ark, Delaware, in 1912. He stated that the fungus had been isolated from corn seedlings that were damping off in the greenhouse. Cotton. Three cultures of Rhizoctonia from cotton received from two sources at different times, were used in these experiments. The strain ' ' Cotton I ' ' was received from Dr. C. W. Edgerton, Baton Rouge, Louisiana, November 12, 1912. This strain was cultured by him in September, 1911, from young diseased plants. The strain ' ' Cotton II ' ' was also received from Dr. Edgerton. This strain was cultured in February, 1912, from the same kind of material as the above. The third strain, "Cotton III," was received from Dr. F. C. Wolf, Auburn, Alabama, December 12, 1912. The fungus was isolated from seedling cotton plants growing in the station greenhouse at Auburn. Dlanthus. Cultures of Rhizoctonia were isolated during July, 1913, from diseased plants of several species of Dianthus growing in the perennial garden. The strains cultured and used in the experiments were ' ' D. b'arbatus N. P., " " D. barbatus S. M., " " D. plumarius, ' ' and ' ' D. sequeri. ' ' Eggplant. Two strains of Rhizoctonia were isolated from eggplant: one, causing a fruit rot, was cultured August, 1912 ; the other was isolated from seed- lings damping off in flats in the vegetable-gardening greenhouse, July, 1913. Gypsophila repens. A culture of Rhizoctonia was isolated during July, 1913, from diseased Gypsophila plants in the perennial garden. Lavatera. A culture was isolated in 1913 from seedlings of lavatera found damping off in pans in the floricultural greenhouses. Lettuce. The strain from lettuce was obtained by Mr. Anderson in 1911, from Cornell University. Poinsettia. Cultures were obtained from damping-off poinsettia cuttings found in the floricultural greenhouses, October, 1912. Potato. Several strains from potato were used in these experiments. Two of these strains were obtained from scrapings o-f the hymenial layer of the Corti- cium stage. "Potato R.P.C. " A culture of this strain was isolated from fresh potato stems received from Dr. I. C. Jagger, Williamson, New York, September 2, 1912. This material contained the perfect stage, Corticium vagum B. & C. Pure cul- tures of Rhizoctonia were obtained from scrapings of the hymenial layer. "Potato R.P.I." In response to a letter from Mr. Anderson, Dr. Geo. H. Pethybridge, Clifden county, Galway, Ireland, sent a small box of potato stems containing the perfect stage, Corticium vagum B. & C. This material was sent by post, July 18, 1912, and received August 5. A pure culture of Rhizoctonia was obtained from scrapings of the gray mycelium of the Corticium stage. ' ' Potato R.P.O. ' ' A culture from potato was obtained by Mr. Anderson from Cornell University. The strain was old and grew very poorly on agar. "Potato R. Sol." This strain, like the preceding one, was obtained by Mr. Anderson from Cornell University. It also grew very poorly on agar. Eadish. A culture of Rhizoctonia from radish was obtained from Cornell University, by Mr. Anderson, in 1911. This form was very old and probably had been in culture several years. It was lost in April, 1913. 340 BULLETIN No. 189 [June, Salvia. The strain from salvia was isolated from cuttings which were found in the same bench with a number of other cuttings damping off, October, 1912. Sedum. A culture of Ehizoctonia from sedum was isolated from diseased plants found in the herbaceous grounds in July, 1913. Sugar Cane. A culture of Ehizoctonia isolated from sugar cane was re- ceived from Dr. C. W. Edgerton, November 12, 1912. This culture was obtained in April, 1912. It was fresh and virulent. Thistle. A culture of Ehizoctonia from thistle was obtained by Mr. Ander- son from Cornell University in 1911. The method of infecting the cuttings, seedlings, and young plants grown in flats and benches, was as follows : Small flats, varying in size with the experiment, were first soaked in a strong solution of formalin for several minutes and then allowed to dry. Steam-sterilized sand or soil and a soil culture of Rhi- zoctonia were then mixed to- gether in the flats and watered. After being tamped down, the flats were left standing for two days in order to allow the fun- gus to spread thru the soil. Later, the cuttings, seeds, or plants were put in the flats and placed in a, chamber in the green- house where the moisture could be controlled. Bottom heat was furnished. The temperature var- ied somewhat during the experi- ment, but the average was about 60 F. When only individual plants in pots or in benches were to be infected, a portion of a cul- ture of Rhizoctonia two weeks old on green-bean plugs was placed in contact with the stem of each plant about one-half inch below the surface of the soil, where it would be protected from light and desiccation. In obtaining soil cultures of Rhizoctonia in large quantities. Mason jars with modified covers were found to be very suitable containers. A hole about one inch in diameter was cut in the FIG. 17. SOIL CULTURE KHIZOCTONIA OF 1916] PARASITIC BHIZOCTONIAS IN AMERICA 341 center of the cover, and a small tin tube about two inches long was in- serted and soldered in. This hole was plugged with cotton. (See Fig. 17.) A mixture of 200 grams of dry sand and 10 grams of corn meal was then placed in the jars and moistened with distilled water until the sand was wet thru. The jars and their contents were then sterilized for one hour at twenty pounds pressure in an autoclave, after which the sand was inoculated with a small piece of infected green- bean plug upon which Khizoctonia was growing luxuriantly. In about a month the soil was permeated with the mycelium, and numerous brown sclerotia of various sizes were formed. When smaller amounts of infected soil were needed, a 250-cc. flask was used. No plant was listed as diseased until a pure culture of Rhizoctonia had been isolated from it. Pure cultures were easily obtained by soak- ing small pieces of diseased parts in 1-1000 mercuric chlorid for two minutes and then placing them on green-bean agar. Rhizoctonia developed rapidly, and in twenty-four to forty-eight hours would spread out from the diseased parts. EXPERIMENTS 1 AND IA: INOCULATION OF CARNATION CUTTINGS WITH VARIOUS STRAINS OF RHIZOCTONIA Rhizoctonia is the fungus most commonly found causing a damp- ing-off of carnation cuttings in the greenhouse. To determine whether any of the strains from sources other than carnation are able to attack carnation cuttings with the same ease as those from carnation, the fol- lowing experiment was carried out. Nine hundred carnation cuttings and 28 strains were used in 1913, and 1,725 cuttings and 34 strains in 1914. Sterilized flats (7x10 inches) were filled with sterilized sand; a 250-cc. soil culture of Rhizoctonia was then added to each and the sand tamped down and watered. One flat was left uninoculated to serve as a check. After two days, thirty carnation cuttings (White Enchantress) were planted in each flat, January 2-3, 1913. The flats were then placed in the moist chamber. The inoculated cuttings began to die in about three weeks (Jan- uary 25), and continued dying until the healthy cuttings had rooted, when the experiment was discontinued (February 11) (Fig. 18). The results are given in Table 3. In most cases the cuttings inoculated with the various strains from carnation showed a soft, wet, progressive rot at the callus, which extended in many cases to the surface of the sand. This rot was very characteristic of the attacks of the carnation strains (Fig. 12). At other times the fungus attacked the cuttings just below the surface of the soil, forming lesions of various sizes at the leaf bases. Myce- lium and sclerotia were also formed along the stems and in practically all cases between the leaves just above the soil. 342 BULLETIN No. ISO [June, TABLE 3. SUSCEPTIBILITY OF CARNATION CUTTINGS TO VARIOUS STRAINS OF EHIZOCTONIA: EXPERIMENTS 1 AND IA Strain Date of isolation Number of plants Experiment 1: 1913 Experiment la: 1914 Healthy) Wilted Dead Healthy Wilted Dead Alfalfa 1910 1912 1912 1913 1913 a . 1913 1911 1911 1911 1911 1911 1912 1912 1912 1912 1913 a 1912 1913 1912 1912 1913 1912 1911 1912 1912 1913 1913 1913 1913 1912 1913 1913 a 1912 1912 1912 a a 1912 1913 1912 a 10 2 3 8 '6 3 19 6 5 1 2 4 '6 ii is 7 4 9 9 10 16 ',3 8 4 14 2 1 "l '6 i 11 2 2 2 3 3 18 6 12 1 2 4 7 6 11 3 18 26 6 26 26 15 30 26 24 23 28 28 26 25 8 30 30 30 30 io '6 22 24 17 14 14 3 24 4 '2 33 3 22 ~4 32 33 12 31 18 4 14 3 8 34 23 24 34 24 46 47 . 5 '6 9 o B 3 2 1 1 2 3 2 '2 1 46 48 48 10 48 48 48 45 17 41 48 14 48 15 36 48 48 14 30 42 34 47 48 48 48 45 40 47 14 25 22 48 11 22 '6 Alternanthera E.A.C. ; . . . ' ' E.A.F Amaranthus Aster Bean Beet Begonia Carnation R.K E.O E.H E.S E.2 E.F B.M.2 R.107 E.F.2 Carrot Cauliflower Chenopodium Clover Coleus I " II Corn Cotton I .... " II " III Dianthus barbatus S.M. . N.P.. plumarius sequeri Eggplant I . II Lavatera Lettuce Poinsettia Potato E.P.C. E.P.I " E.P.O . " B.Sol Salvia Sedum Sugar cane Thistle Check } j > > "This strain had been in culture for a number of years; the exact year of isolation is not known. PARASITIC RUIZOCTONIAS IN AMERICA 343 FIG. 18. EXPERIMENTS 1 AND IA: CARNATION CUTTINGS INFECTED WITH RHIZOC- TONIA STRAINS (1) CARNATION R.K. ; (2) CARNATION R. 107; (3) CAR- NATION R.O.; (4) CARNATION R.F. (5) BEGONIA; (6) COLEUS; (7) POIN- SETTIA; (8) SALVIA; (9) CAULIFLOWER; (10) THISTLE; (11) LETTUCE; (12) POTATO R.P.C.; (13) COTTON; (14) BEAN; (15) POTATO R.P.O.; (16) CARROT 344 BULLETIN No. 189 [June, The percentage of infection was about the same with all the carna- tion strains except "Carnation R.O.," which appeared to have lost practically all power of attacking cuttings. This was one of the first strains isolated from carnation. Thus the age of the strain seemed to play an important role in its virulence, and for this reason the date of the original isolation of each strain is included in the table. The strains from alternanthera, coleus, salvia, and poinsettia, all cf which were isolated from diseased plants in the same cutting bench, produced in some cases a soft wet rot of the carnation cuttings similar to that caused by the carnation strains. In the majority of cases, how- ever, these strains attacked the cuttings at the callus, forming large brow r n sclerotia which covered the whole callus and so prevented the formation of roots. Brown strands of the mycelium and sclerotia were formed on all parts of the cuttings underground and also be- tween the leaves. Occasionally, small lesions appeared at the leaf bases which were slightly under the surface of the sand. The two strains from alternanthera and the one from poinsettia killed about the same number of cuttings as the strains from carna- tion, while the one from coleus caused 100-percent infection and rotted the cuttings off faster than the strains from carnation. The percent- age of infection with the strain from salvia was very low. The strain from begonia produced a soft rot somewhat different from that produced by the carnation strains. It appeared on the stem at the surface of the soil and sometimes at the callus. The fungus formed a dense mass of mycelium which completely covered the sand beneath. Here again the virulence was greater than with the carna- tion strains, all the cuttings being killed and in a much shorter time. The strains from eggplant, lettuce, and thistle for the most part formed many sclerotia on the stems and in between the leaves of the cuttings, with only an occasional sclerotium at the callus. Small lesions were found to be abundant at the leaf bases and on the stems. These strains were very weak, especially those from lettuce and thistle, which had been in culture for a number of years. The cuttings infected with strains from cotton, cauliflower, and sugar cane rotted off at the surface of the soil; the rot started as a lesion at this point and progressed very rapidly until the cutting was killed. Smaller lesions were produced on the stem underground. Sclerotia and the brown strands of the fungus could be found in abundance on the parts below the soil. The strains from cotton and cauliflower were very virulent; all the cuttings inoculated with them were killed one week before the cuttings inoculated with a soil culture of the carnation strains began to die off. The potato strains, as a rule, produced a large number of sclerotia and a dark brown mycelium below the soil and on the leaves. The percentage of infection was fairly high and uniform altho the average was below that of the carnation strains. 1916] PARASITIC RHIZOCTONIAS IN AMERICA 345 The strains from alfalfa, bean, and carrot produced symptoms simi- lar to those from potato. A large number of the cuttings placed in the uninoculated sand wilted, but none became diseased. During the spring of 1914, beginning on March 7 and ending on April 7, the experiment was repeated, the only difference being that a number of additional strains were used and flats containing forty- eight cuttings instead of thirty. As will be seen in Table 3, the re- sults were confirmatory. The marked increase in the virulence of the lettuce strain may have been due in part to the influence of tempera- ture both on the strain and on the cuttings. EXPERIMENTS 2 AND 2A; INOCULATION OF YOUNG CARNATION PLANTS WITH VARIOUS STRAINS OF RHIZOCTONIA That the majority of strains can attack carnation cuttings was shown in Experiments 1 and la, where it appeared that the virulence of the strain did not depend on the host from which it was originally isolated, but in some cases did depend on the length of time since the culture was isolated. To determine whether rooted plants were as susceptible to these various strains of Rhizoctonia as were cuttings, further experiments were carried out : Experiment 2 in 1913, involv- ing about 400 young plants and 24 strains; and Experiment 2a in 1914, in which about the same number of plants but only 13 strains were used. Carnation cuttings (White Enchantress) which had been placed in sterilized sand December 12, 1912, were planted February 12, 1913, in sterilized flats (9x12 inches) containing sterilized soil, fifteen plants in each flat. Plants failing to strike root were pulled out, leaving an unequal number in the various flats. The flats were inoculated on March 23 with 250-cc. soil cultures of Rhizoctonia, each flat with a different strain. They were then placed in a case in the greenhouse and left during April and May. Usually the carnation strains, as in the case of the cuttings (Ex- periments 1 and la) , produced a soft, wet rot at the surface of the soil or just below. On other plants they caused small lesions of various sizes along the stems, killing the plants slowly. Sclerotia and brown strands of mycelium were as a rule present on plants which showed lesions and on others less badly diseased. Only an occasional plant in the flats infected with other strains than carnation developed a soft, wet rot. In the majority of cases where infection took place the strains produced lesions of various sizes on the stems at the surface of the soil or just below, slowly killing the plants (Fig. 13). As a rule, sclerotia and mycelium were also present on the stems of the infected plants. The plants in the check flat re- mained healthy. 346 BULLETIN No. 189 [June, The resistance of the rooted carnation plants to the fungus, as shown in Table 4, was much more marked than with the cuttings. In the few exceptions the fungus appeared able to infect the plants al- most as readily as it had the cuttings. In 1914 this experiment was essentially repeated. Thirty young car- nation plants (Rosette) were placed in each of a number of flats (12x18 inches) . On April 26, after the plants were rooted, some of the old infected sand from the inoculated flats used in Experiment la was mixed with the soil in which the plants were growing. The experiment was continued until June 1. The results, which are presented in Table 4, were similar to those of Experiment 2. As in that experiment, the plants in the check flat remained healthy, with the exception of two that wilted and died from attacks of a Fusarium. TABLE 4. SUSCEPTIBILITY OF YOUNG ROOTED CARNATION PLANTS TO VARIOUS STRAINS OF RmzocTONrA: EXPERIMENTS 2 AND 2A Strain Number of plants Experiment 2: 1913 Experiment 2a: 1914 Total {Healthy] Dead Total Healthy) Dead Alternanthera R A.C 15 - 15 12 5 ii 2 'i 6 2 2 4 13 9 9 2 8 10 'G 13 15 7 8 10 13 12 15 3 10 'i 12 is 7 12 15 12 11 2 6 6 13 7 4 - 9 '2 7 6 5 2 2 30 30 30 30 30 30 30 30 30 30 30 30 30 SO is 25 20 is is io 22 23 13 12 24 19 24 28 12 5 10 15 15 20 's 7 17 18 6 11 '6 'JJ- " R.A.F Amaranthus Beet Begonia 15 14 Carnation R K R.H R.S 14 13 14 15 14 15 15 15 15 15 15 14 15 15 15 14 14 15 15 14 15 R.2 R.F R.F R.M.2 R.107 R.F.2 Carrot Cauliflower Coleus I Cotton I " II " III Dianthus barbatus N.P Efjtmlant I . Lavatera Lettuce Potato R.P.C " R.P.I " R.P.O Salvia Sedum Sugar cane Thistle Check "Killed by Fusarium. 1916] PARASITIC RHTZOCTONIAS IN AMERICA 347 EXPERIMENT 3: INOCULATION OF OLD CARNATION PLANTS IN POTS WITH VARIOUS STRAINS OF RHIZOCTONIA The resistance of young rooted carnation plants to the various strains of Rhizoctonia other than those from carnation was very marked in Experiments 2 and 2a. To determine whether or not old carnation plants were even more resistant, the following experiment was carried out, involving 90 plants and 18 strains. Carnation plants (White Enchantress and White Perfection) were brought in from the field and planted in pots, which were then placed in the bench. The plants were grown under the best possible cultural conditions and on November 27, 1912, when they had become firmly established, they were inoculated. Five plants of the same size were used for each test, one being left as a check. The other four were inoculated by placing a bit of infected green-bean plug near the stem about one-half inch below the surface of the ground. The stems of two plants of each test were slightly wounded before the plugs were placed by them. Observations were discontinued on March 27, four months later. The results are presented in Table 5. Only two plants inoculated by contact died during the course of the experiment, and both were killed by carnation strains. However, where the stem was slit, the various strains were in most cases able to infect and kill the plant. The check plants remained healthy during the experiment. TABLE 5. SUSCEPTIBILITY OP OLD CARNATION PLANTS (IN POTS) TO VARIOUS STRAINS OP RHIZOCTONIA: EXPERIMENT 3 Strain Plants inoculated by Check plants Contact Slit Healthy I Diseased Healthy Diseased Healthy I Diseased Alternanthera R.A.F 2 2 2 2 1 1 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 . 2 1 1 1 2 2 o 2 2 2 1 2 1 2 2 2 2 1 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Carnation R.K R.O R.H R.S. R.2 R.F R.M.2 R.107 Carrot Cotton II Eggplant I Lettuce Poinsettia Potato R. Sol " R.P.O " R.P.I Thistle . 348 BULLETIN No. 189 [June, EXPERIMENT 4: INOCULATION OF YOUNG CARNATION PLANTS WITH ISOLATED AND WITH REISOLATED STRAINS OF RHIZOCTONIA The object of Experiment 4 was to compare the virulence of various strains of Rhizoctonia when they were inoculated on carnation plants for the first time, and after they had been inoculated on carnation and reisolated. Fifteen strains, taken at random, and about 300 plants were used. On December 12, 1912, a number of carnation cuttings were made and placed in sterilized sand. They were allowed to remain in the sand until well rooted. On March 22, when the plants were from four to six inches high and breaking nicely, they were placed in three- inch pots in sterilized soil. They were then inoculated by placing a bit of bean pod infected with Rhizoctonia near the stem just below the surface of the soil. Table 6 gives the results obtained. With seven strains the virulence of the reisolated fungus was slightly greater than that of the original isolation. With two it was slightly less. TABLE 6. COMPARATIVE VIRULENCE OF ISOLATED AND EEISOLATED STRAINS OP EHIZOCTONIA WHEN INOCULATED ON YOUNG CARNATION PLANTS (IN POTS) : EXPERIMENT 4 Strain Original isolation Reisolation Healthyl Diseased Healthy! Diseased Bean 9 6 1 4 *5 4 3 "(5 6 1 1 9 1 1 2 (5 7 4 3 7 5 10 7 10 8 9 1 9 9 8 5 3 6 7 3 5 3 2 1 Carnation B.K R.K E.H 5 G 10 7 R S R2 R.F R F R.M.2 4 4 10 9 10 9 10 10 10 10 R.107 Cauliflower Cotton I " n Potato RPI Sugar cane Check > > ' ' EXPERIMENT 5: INOCULATION OF OLD CARNATION PLANTS IN THE BENCH WITH VARIOUS STRAINS OF RHIZOCTONIA Experiment 5 was similar to the preceding experiment except that the carnation plants used were older and were grown in the bench in- stead of in pots, and that inoculations were made with only eight strains of Rhizoctonia, chosen at random. 1916} PARASITIC KHIZOCTONIAS IN AMERICA 349 On September 1, 1913, the soil in two five-foot sections in the green- house was sterilized, and twenty carnation plants from the field were placed in each section, four plants in a row. Four rows in each sec- tion were each inoculated with a different strain of Ehizoctonia, by means of pieces of infected bean plugs. The middle row in each sec- tion was left as a check. The plants began to die off at the end oi three weeks and con- tinued dying until the close of the experiment, October 31. They all died in a manner characteristic of stem rot. All the strains used proved to be virulent except the one from beet (see Table 7). The check plants remained healthy thruout the experiment. TABLE 7. SUSCEPTIBILITY OP OLD CARNATION PLANTS (IN THE BENCH) TO VARIOUS STRAINS OF EHIZOCTONIA: EXPERIMENT 5 Strain ]Healthy | Diseased Beet 3 1 Carnation R.107 4 Cauliflower 1 3 Cotton II 4 Dianthus barbatus S.M 1 3 plumarius . 4 Eggplant I . 1 3 Potato B. Sol 1 3 Check 4 7 > 4 The high mortality of the strains in this experiment was due, to a large extent, to the date of inoculation. The plants in the preceding experiments were inoculated either late in the fall or in the early spring, when the temperature in the greenhouse was low and normal and not influenced by outside conditions. The temperature in the house during September and October, when these plants were inocu- lated, is very high ; hence the virulence of the fungus was much greater. The effects of inoculating plants at various times of the year are clearly brought out in the next experiment. EXPERIMENT 6 : INOCULATION OF CARNATION PLANTS WITH Rmzoc- TONIA AT DIFFERENT TEMPERATURES During the season 1913-14 a number of sections containing carna- tions were reserved in the greenhouse, and at different times of the year the plants were inoculated with RMzoctonia from carnation. This experiment was for the purpose of ascertaining the relative virulence of Rhizoctonia when inoculated on carnation plants at dif- ferent temperatures. Each section contained twenty plants, sixteen of which were in- oculated by placing infected bean plugs at the base of the stem. The remaining four plants served as checks. 350 BULLETIN No. 189 [June, TABLE 8. RELATIVE VIRULENCE OF EHIZOCTONIA INOCULATED ON CARNATION PLANTS AT DIFFERENT TEMPER \TURES: EXPERIMENT 6 Section Date of inoculation Experiment discontinued Inoculated plants Check plants Healthy Diseased Healthy 1 Diseased 143 Sept. 1, 1913 Oct. 1, 1913 1 15 4 140 Oct. 1, 1913 Nov. 1, 1913 3 13 4 139 Nov. 1, 1913 Jan. 1, 1914 10 6 4 138 Dee. 1, 1913 Feb. 1, 1914 8 8 4 137 Jan. 1, 1914 Mar. 1, 1914 14 2 4 134 Feb. 1, 1914 Apr. 1, 1914 3 13" 4 133 Mar. 1, 1914 May 1, 1914 12 4 4 132 Apr. 1, 1914 June 1, 1914 9 7 4 131 May 1, 1914 July 1, 1914 16 4 130 June 1, 1914 July 1, 1914 2 14 4 128 July 1, 1914 July 23, 1914 6 10 4 Ten plants found infected April 1; only three plants died during the months of February and March. As can be seen from Table 8, the death rate of the plants inocu- lated on September 1 and October 1 was almost 100 percent. This rate diminished very markedly when the plants were inoculated later in the season, increasing with the plants inoculated during the spring months until with those inoculated on May 1, it had again reached a high percentage. This condition prevailed during the summer months, showing very noticeably the influence of temperature on mortality. EXPERIMENT 7: INOCULATION OF VARIOUS HOSTS (SEEDLINGS) OTHER THAN CARNATION WITH VARIOUS STRAINS OF RHIZOCTONIA In the preceding experiments all the work was carried on with carnation plants of different ages. It was found that under certain conditions all the strains used could attack these plants, but that the resistance was somewhat increased when the plants were rooted. To determine whether the same results could be obtained with other plants, a number of further experiments were made. Small flats (8x10 inches) were disinfected and filled with a mix- ture of sterilized sand and soil suitable for germinating seed. In each flat a 250-cc. soil culture of one of the various strains used was thoroly mixed with the soil, and the whole allowed to stand for several days. The seeds, after a short soaking in formalin (1-150), were sown in the flats, thirty-one in all, care being taken not to plant them too closely. Nine different kinds of seedlings and 13 strains w r ere used in the ex- periment. The results obtained are given in Table 9. In the first group of the various hosts, clover proved to be more resistant than alfalfa, while the injury to corn roots was negligible. Of the different strains, the one from clover proved the most virulent, while the one from corn was the weakest (Fig. 19). 1916] PARASITIC EHIZOCTONIAS IN AMERICA 351 TABLE 9.- -SUSCEPTIBILITT OF VARIOUS PLANTS (SEEDLINGS) OTHER THAN CARNA- TION TO VARIOUS STRAINS OF KHIZOCTONIA: EXPERIMENT 7 Group 1 Strain On clover On alfalfa On corn Olov6r 150 seeds 150 seeds 30 seeds Most of seedlings killed at germina- tion; 6 came up; 5 infected below surface of ground, showing lesions ; 1 healthy All seeds attacked by fungus at ger- mination. Ehizoc- tonia present in seeds Plants 4-6 inches high. Seed in all cases showed the presence of Bhi- zoctonia, but whether it would kill the whole Alfalfa .... Abbut 15 percent 80 percent damped plant is a ques- damped off in typ- ical manner. Le- sions at surface of ground off. Others in va- rious stages of in- fection. 5 percent healthy tion. However, fungus is able to live in the roots of the corn. Cul- Carnation R. 107. . Only few plants infected. First leaves of a large number dead from effects of fungus 70 percent damped off. Condition sim- ilar to that of plants inoculated with alfalfa strain tures of Ehizoc- tonia were ob- tained from the seeds Corn 2 percent damped 8 percent damped off. Ehizoctonia present on the roots of living plants, but did not seem virulent off. Eemaining plants healthy Group 2 Strain On lettuce On eggplant On cabbage Lettuce 150 seeds 150 seeds 90 percent damped off. Lesions on stem at surface of ground. Leaves also attacked, causing a rot 2 percent damped off. Lesions at surface of ground. Typical Eggplant I 75 percent damped 34 percent damped off. Lesions typi- cal, like lettuce off. Typical Thistle (50 percent damped 5 percent damped off. Lesions typi- cal, like those ori plants inoculated with eggplant strain. Action of fungus slower but virulent off. Small circular lesions present. Typical Carnation E.F 60 percent damped off. Like thistle ; slower in effect, but still virulent All healthy 40 percent infected. Lesions in form of a collar around stem at surface of ground Cauliflower 3 percent damped Only 3 plants off. Typical le- sions healthy. Seedlings attacked at ger- mination 352 BULLETIN No. 189 TABLE 9. Concluded [June, Group 3 Strain On radish On turnip On beet Radish 150 seeds 150 seeds 1 percent infected at base of stems. Several completely rotted Seedlings attacked at germination. Only 2 healthy plants Potato R.P.C. . . . 15 percent infected at base of stems where root begins. Small wounds like potato scab due to Rhizoctonia off. Some rotted off at the ground Carrot Seedlings attacked 50 percent infected at germination. Only 3 healthy plants All showed collar rot. Some rotted off Carnation R.F. . . 50 percent infected. Lesions at base of stems. Few rotted off 98 percent damped off. Showed collar rot. Typical FIG. 19. EXPERIMENT 7 : UPPER Row : ALFALFA SEEDLINGS INFECTED WITH RHIZOCTONIA STRAINS (1) CLOVER; (2) ALFALFA; (3) CARNATION R. 107! (4) CORN. LOWER Row: LETTUCE SEEDLINGS INFECTED WITH RHIZOCTONIA STRAINS (1) LETTUCE; (2) EGGPLANT I; (3) THISTLE; (4) CARNATION R.F. Of the seedlings in the second group, lettuce and cabbage were quite susceptible ; eggplant seedlings were very resistant. The strain from cauliflower, altho it caused only a slight damping-off of lettuce 1916] PARASITIC EHIZOCTONIAS IN AMERICA 353 seedlings, produced practically 100-percent infection in the case of cabbage seedlings (Fig. 19). In the third group, beet, radish, and turnip seedlings proved very susceptible to damping-off of Rhizoctonia. It is rather interesting to observe that while the strain from radish was able to cause only 1-percent infection of radish seedlings, it caused almost 100-percent infection of turnip seedlings. Taking the experiment as a whole, it is seen that a great variation exists in susceptibility of seedlings and in virulence of strains. It is clear that under certain conditions all the strains can attack a given host with about the same virulence. EXPERIMENT 8: INOCULATION OF VARIOUS HOSTS (OLD) OTHER THAN CARNATION WITH VARIOUS STRAINS OF RHIZOCTONIA In Experiment 8 the preceding experiment was carried one step farther, older plants being used rather than seedlings. A number of plants were taken from flats while small and transplanted to four-inch pots, where they were allowed to grow for about two months. The soil in these pots was not sterilized. Each plant, with the exception of the check plants, was inoculated by placing an infected bean plug in contact with it just below the surface of the soil. Four kinds of plants, 50 of each, and 12 strains were employed. The observations from this experiment are recorded in Table 10. In Group 1, the tomato plants proved resistant to the attacks of the various strains, with the exception of the one from carnation, which produced a slight infection on two plants. In the case of the cabbage plants, the strains from cotton and from cauliflower exhibited a marked specialization, producing 50- and 90-percent infection, respectively, on these plants, while on tomato plants they produced no infection what- ever. Cabbage was the only host in the experiment susceptible to all the strains with which it was inoculated. The carnation strains in Groups 2 and 3 also proved more virulent than the other strains, producing 50-percent infection on lettuce and 100-percent infection on beet (Fig. 9). Of the other strains, eggplant alone was able to attack the plants, producing a slight infection on two lettuce plants. EXPERIMENT 9: INOCULATION OF VARIOUS HOSTS (CUTTINGS, SEED- LINGS, AND LARGER PLANTS) WITH VARIOUS STRAINS OF RHIZOCTONIA The kinds of plants used in the foregoing experiments were some- what limited. Increased facilities being at hand in the spring of 1914, a more extensive series of inoculations was made with cuttings, seed- lings, and larger plants of various kinds. In all, about 350 cuttings, 3.000 seedlings, and 300 larger plants were inoculated. Thirty-two strains of Rhizoctonia were used. 354 BULLETIN No. 181) [June, co W S EH * ow 5 .2 1 .9 J! 'S'^'i.^ >>>>>> ^ T3 ^ S In "*"" "So 1* 5 5 ^ _^ -2> d ^ 2 ^H ^H ^p cd cd 03 "3 cu d O ^ r-i 0? O O> O) T)*^! 13 a '^ K. ^ ^ rd -d rd i4 " H~"i3 rrt <5 3 ^ .~*5 t< +> toroo? no CO Pi d 42 4j j3 o3n r OjS d gx-s PH PH PH PHCS^g-M.S * H0> o o o a 'En O o CO 1-1 W rH r-t iH Tl E ._ o O q d ^M '3 ^J IH d CO o "S jj o ja -S ro Jrf d * a *r3 CJ o> OS 3 "S C3 ja O d. M O 11 ^ 111 ^ to 5 rt ?3 to ^ 13 -i 13 "3 3 -d ;g T3 j ^ s 03 d>- CD O3 t*> r^ to to p d s "^ a S fl P] "5 43 c &jo 43 w 43 43 %* ^ m I I ls' rt s OI O> d d K WJ O g O ^ ^> g 9 .2 t, a ip s S '3. 2 o T3 S.&o "3 O S OT 8 4 13 ,5 03 rt o i " >, "3 || PH in 2 "* *> 111 ill PH 03 CO S ,0 P< 5 OQ s 43 "E o OO > ' ^ fl 1 1J ! 3* * a fr >' p. 3 O (H tomato 1 13 .2 '3 a>'~' o^o 03 ^ Md-,i)- B o O o H| 00 oq 1 1 iH ii IQ iH .5 Tl -l Pj s CO oj O o H d F-4 et S o 03 d t H S JH c3 6 1 e 1916] PARASITIC RHI/.OCTONIAS IN AMERICA 355 Flats (9x12 inches) were infected as in Experiment 7, and a vary- ing number of cuttings, seeds, and plants placed in them on March 7, 1914. Pure cultures from the diseased plants in each flat were made, and Rhizoctonia was isolated in each case. Following, the results of the experiment are taken up in detail. " Alternanthera E.A.C." on Alternanthera. 48 cuttings. On March 18 all were dead. The infection was first noticed as a small, brown lesion on one side at the surface of the ground; later the lesion girdled the whole stem. The fun- gus also attacked the cut surface of the cutting, causing a lesion and in some instances a slow, wet rot. The mycelium, which grew very profusely, attacked the leaves, producing a characteristic rot. "Alternanthera E.A.F." on Alternanthera. 48 cuttings. The experiment was carried out exactly like the above and produced the same results. "Alternanthera E.A.F." on Gernanium. 48 cuttings. These were planted March 20 in the infected flat in which alternanthera cuttings had died. By May 2, 42 of them were rotted while 6 were rooted and healthy. "Amaranthus" on Amaranthus salicifolius. 100 seeds. Seeds germinated March 23, and by April 1 all the plants in the flat damped off in a character- istic manner. "Aster" on Aster. 100 seeds. Seeds germinated March 18 and a few be- gan immediately to damp off. By April 1, 29 percent had died, while the others remained healthy. "Bean" on Bean. 30 seeds. Seeds germinated March 19, and after two months only 5 percent were killed by the fungus. . "Beet" on Beet. 100 seeds. Seeds germinated March 19 and began to damp off. About 25 percent damped off and later about 25 percent more be- came scabby because of the formation of small, depressed lesions. Injury here was similar to the infection of beet by the strains from carnation. ' ' Carnation ' ' on Bean. 50 plants. On May 8, bean plants about three inches high were transplanted from flats to infected sections (Nos. 157 and 173). The plants took hold readily, and after about two weeks began to show signs of infection. The disease progressed rather slowly ; most of the plants produced a few pods before they were killed by the fungus. When pulled up, May 19, every one was diseased or dead (Fig. 8). A detailed description of four typically infected bean plants follows. It will be seen that it corresponds in most details to the descriptions given by Barrus, 9 Fulton, 45 and Hedgcock 60 Plant No. 1: Three distinct lesions were present, one directly above the other on the stem. Lesions were oval in shape with a reddish brown band surrounding a lighter colored sunken area. Evidences were present of young lesions over the entire stem and larger roots under- ground. The wounds extended beneath the cortical layer to the woody tissue. Plant No. 2: Eoots were infected at the joint of their union with the main stem. The lateral root was very badly infected and rotted off entirely. The lesions on the smaller roots were small, depressed, and of a reddish brown color. Plant No. 3: A large, reddish brown lesion extended from the sur- face of ground downward 2.5 centimeters. Spots were sunken and ex- tended thru the cortex to woody tissue beneath. Two small sunken areas of a reddish brown color were present on the stem one inch above the sur- face of the ground. Plant No. 4 : A large, depressed, reddish brown area extended from the surface of the ground downward 2.5 to 3 centimeters, almost encircling the stem. Cortical tissue rotted away exposing the woody tissue beneath. "Carnation" on Beet. 30 plants. On May 8, young beet plants were trans- planted to a section (No. 158) infected with Rhizoctonia from carnation. By 356 BULLETIN No. 189 [June, May 20 they all showed some scab. A number were infected at the crown, where a large number of leaves were completely cut off at the base by the fungus. Sev- eral beets had depressed lesions which extended deep into the tissues. "Carnation" on Cabbage. 25 plants. On May 8, young cabbage plants were transferred from flats to a section (No. 163) in the greenhouse infected with a soil culture of Khizoctonia from carnation. Some of these plants grew to maturity, but when they were pulled up, May 21, the stems and roots were cov- ered with black, depressed lesions (Fig. 11). Ninety percent of the plants set in the bench were infected in this way. Where the leaves touched the soil the fun- gus caused a slow, wet rot. ' ' Carnation ' ' on Carrot. 50 plants. Carrot plants were transferred on May 8 from flats to an infected section (No. 158) in the greenhouse. By May 21 only a few had rotted. The rot started at the crown, where the petioles were attacked, and worked down into the tissues of the root and up into the leaves. The rot from the crown goes into the interior of the root, and thus the root does not show any signs of rot on the outside for some time. Occasionally lesions were found on the sides of the carrots and on the larger roots where they branched from the fleshy part. "Carnation" on Corn. 10 seedlings. Corn seedlings about 8 inches tall were transplanted on May 8 from flats to an infected section (No. 153) in the greenhouse. The plants grew to maturity. When pulled up, only small lesions were to be found on the roots. These were only slightly depressed and did not retard the growth of the plant. "Carnation" on Eggplant. 25 plants. On May 8, eggplants were trans- ferred to an infected section in the greenhouse (No. 170). The plants reached maturity with no loss. When they were pulled up, no infection was to be found. "Carnation" on Lettuce. 60 plants. On March 16, lettuce plants were transferred to an infected section (No. 153). By March 24, 16 percent of the plants were killed. No more loss occurred and the plants were cut on April 21. "Carnation B. 107" on Cabbage. 100 seeds. Seeds germinated March 19 and began to damp off immediately. By May 21 those which did not damp off were infected in various ways. Some had constrictions just at the surface of the soil; others had definite lesions along the stern and larger roots. Where the plants were crowded, spots of various sizes were formed on the lower leaves which touched the soil. ' ' Carnation E.M.2 ' ' on Carrot. 150 seeds. Seeds germinated March 18. When the experiment was discontinued, May 21, only 10 percent of the carrots were infected at the crown. One showed a constriction which was quite marked. "Carnation R.F." on Beet. 100 seeds. Seeds germinated March 16 and began to damp off immediately, so that by March 24, 40 percent of the plants were dead. The remainder, when examined on May 21, were all more or less scabby. Some were rotted at the crown. ' ' Carnation E.F.2 ' ' on Bean. 30 seeds. Seeds germinated March 19. When the experiment was discontinued, May 8, but slight infection could be noticed. "Carrot" on Carrot. 150 seeds. Seeds germinated March 16. By May 21 only a few of the carrots were infected. An occasional plant showed crown rot, which was especially noticeable at the base of the leaves. "Cauliflower" on Cabbage. 100 seeds. Seeds germinated March 13. A few seedlings began to damp off March 14 and by May 21 most of the plants were infected. Lesions could be found on the stems, occasionally one girdling the whole stem and forming a sort of constriction as the plant developed. A number of spots varying in size could also be found on the lower leaves which touched the soil. "Chenopodium" on Alfalfa. 100 seeds. Seeds germinated March 13. Two weeks later 60 percent of the seedlings had damped off in a characteristic manner. "Clover" on Clover. 150 seeds. Seeds germinated March 12 and began to damp off slowly. By March 21, however, the plants had reached sufficient size so that no more damping-off occurred. In all about 10 percent of the seed- lings were diseased. 1916] PARASITIC BHIZOCTONIAS IN AMERICA 357 "Coleus I" on Coleus. 100 seeds. The seeds were all killed by the fun- gus as they were germinating. "Coleus I" on Coleus. 48 cuttings. By March 18 all the cuttings had rotted off. Infection began as small spots at the surface of the ground or at the callus. Underground lesions of all sizes were produced, from small spots to places where the whole stem was girdled. The leaves of the cuttings were over- run with mycelium, the fungus in many cases rotting them off. "Coleus II" on Chrysanthemum. 48 cuttings. The old infected flat in which the coleus cuttings had rotted off was planted to chrysanthemum cuttings March 20. By March 27 all of them had rotted off at the surface of the ground. In some a soft, wet rot was produced. "Coleus II" on Coleus. 100 seeds. Seeds germinated March 24 and began to damp off slowly. By May 21 only 30 percent of the plants were still healthy. "Coleus II" on Coleus. 48 cuttings. All cuttings rotted off as with "Coleus I. ' ' The red-colored cuttings rotted off faster and were much more susceptible than those of the green variety. "Corn" on Corn. 50 seeds. Seeds germinated March 17. The plants grew to maturity. When pulled up, no signs of infection were noticed. "Cotton I" on Cotton. 50 seeds. The fungus caused a rotting of the seeds as they germinated. "Cotton III" on Cotton. 50 seeds. Eesults same as preceding. "Dianthus barbatus S.M." on Dianthus barbatus (Sweet William). 100 seeds. Seeds germinated March 19 and began to damp off immediately. By May 22, 50 percent of the seedlings were diseased. "Dianthus barbatus N. P." on Dianthus barbatus (Sweet William). 100 seeds. Eesults same as preceding. ' ' Dianthus plumarius ' ' on Dianthus plumarius. 100 seeds. Seeds germinated March 14. By May 22, 80 percent of the plants had damped off. "Dianthus sequeri" on Dianthus sequeri. 100 seeds. Seeds germinated March 18 and began to damp off immediately. By May 22 only about 25 percent were still healthy. "Eggplant I" on Eggplant. 150 seeds. Seeds germinated March 23. By May 8 only 3 to 4 percent of the plants had damped off. "Eggplant II" on Eggplant. 150 seeds. Seeds germinated March 23. The fungus caused a rot of the seeds at germination. "Lavatera" on Lavatera trimestris. 100 seeds. Seeds germinated March 12. By May 22 about 25 percent of the seedlings had damped off (Fig. 14).. On the remainder, lesions of various sizes were present, which in some cases girdled the stem just below the surface of the soil and formed a collar, or constriction. ' ' Lettuce ' ' on Lettuce. 125 seeds. Seeds germinated March 13. By April 1 all the young plants had damped off. "Poinsettia" on Euphorbia variegata. 100 seeds. Seeds germinated March 23. By May 22, 6 percent of the plants had damped off. "Salvia" on Salvia splendens.- 100 seeds. Seeds germinated March 23. By May 8, 6 percent of the seedlings had damped off. By May 21, 4 of the plants were infected. Lesions extending into the woody tissues were present on the stem. "Salvia" on Salvia splendens. 48 cuttings. These cuttings rotted off very rapidly. Wherever the leaves touched the soil, they were rotted also. By April 7, 41 cuttings were diseased and 7 were rooted and healthy. "Sugar Cane" on Amaranthus salicifolius. 100 seeds. Seeds germinated March 23. On May 21 all the plants were perfectly healthy. No infection waa present. "Thistle" on Clover. 100 seeds. Seeds germinated March 13. On May 21 all the plants were healthy. Additional Inoculations. On April 1 six flats of infected soil used in the inoculation experiments with carnation cuttings were mixed with soil in larger tlats and four hills of potatoes were planted in each. The six flats represented the 358 BULLETIN No. 189 [June, six strains " Alternanthera B.A.F.," "Carnation R.F.," "Cauliflower," "Let- tuce, ' ' " Cotton, ' ' and ' ' Dianthus barbatus. ' ' Only one or two potato sprouts came up from each hill and these were weak and spindling. After the tempera- ture became too high in the greenhouse, the flats were placed outside, so that the plants would develop further and produce tubers. The strains killed some of the young sprouts and dwarfed the others, showing that they were able to attack the potato plant. Here, as in the preceding experiments, the death rate of the vari- ous plants was quite variable. These differences appear to be due to the virulence of the fungus, to the susceptibility of the plant, or to a combination of factors. EXPERIMENT 10 : INOCULATION OF VARIOUS HOSTS IN THE FIELD WITH VARIOUS STRAINS OF RHIZOCTONIA All the inoculation experiments reported so far were conducted in the greenhouse. In the summer of 1914 a fourth of an acre of land was divided into three parts, separated by six-foot strips of ground. Sec- tion 1 was inoculated on May 20 with twenty cubic feet of infected soil taken from the inoculated benches in the greenhouse. The soil was spread upon the section, worked under, and watered for several days. Section 2 was left as a check. In Section 3 small bits of pure cultures of various strains of Rhizoctonia were added with the seeds and plants. The seeds were planted May 20, and the young plants were put in June 16. Altho the drouth of the summer interfered considerably, the results obtained were sufficient to show that Rhizoctonia Solani was active under field conditions as well as in the greenhouse. No infection occurred in the first two sections. In Section 3 in- fection was quite marked in a number of cases, especially on cotton, potato, and several greenhouse plants. Where the strain ' ' Cotton I ' ' was added to the cotton seeds, 100-percent infection occurred. In the case of potato, to which ' ' Carnation R.F.2 ' ' was added, a marked dif- ference was noticed, the plants in this section being dwarfed and spindling, while in the first two sections they were bushy and strong. The difference in the yield was as marked as the difference in growth of the plants. All the coleus plants infected with "Coleus I" were killed within two weeks after being set out. The same results were obtained from inoculating salvia plants with the strain from salvia. DISCUSSION OF INOCULATION EXPERIMENTS In Table 11 are brought together, in tabular form, the results of all the inoculation experiments, with the exception of No. 4, which was carried on primarily to test the comparative virulence of isolated and reisolated strains of Rhizoctonia. The thing that stands out at first glance is the great variation in the mortality of the plants when inoculated with strains from the same host and when inoculated with strains from other sources. 1016] PARASITIC KHIZOCTONIAS IN AMERICA 359 When carnation cuttings were infected, the strains used, with but two exceptions, whether from carnation or from other hosts, were able to cause more or less loss, the mortality of the cuttings ranging in either instance from to 100 percent. Again, the same strains varied in virulence from one year to another, in most cases decreas- ing in virulence with age. When cuttings other than carnation were used, the results were the same. When young rooted carnation plants were inoculated, the percent- age of loss was much less than with cuttings. Here, however, the car- nation strains seemed to be slightly more virulent than those from other sources, altho there was still a great difference in the strains from carnation themselves. Only one of the strains from other sources was unable to attack young rooted carnation plants. On old carnation plants in the greenhouse which were inoculated by contact, even the carnation strains did not cause a high percentage of infection. However, when plants growing under these same condi- tions were slightly wounded and then inoculated, the percentage of loss was very high in nearly all the strains studied. When conditions (temperature and moisture) were favorable to the fungus, most of the strains studied were able to infect carnation plants as readily as the carnation strains themselves. In the majority of cases all strains were able to cause damping-off of various seedlings. There was a great difference in the virulence of strains when inoculated on the same host from which they had been isolated and when inoculated on other hosts. Only occasionally was there any indication of marked specialization, and in no case was such indication corroborated in succeeding experiments. In older plants, a marked difference in susceptibility was found in the different species. As a rule, the root crops were highly susceptible to attacks of Rhizoctonia. Among these, beet appeared to be the most susceptible. Tomato and eggplant showed a very marked resistance to Rhizoctonia, and this was true to some extent of the potato also, altho under certain conditions it was quite susceptible. This varia- bility of resistance held true for most of the vegetable and field crops other than root crops. Under ordinary conditions, the majority of floricultural plants were not subject to attacks of Rhizoctonia, altho the mycelium of this fungus was known to be present in the soil or even on the plant itself. From the fact that all the strains studied showed the ability to attack the same species of plant and produce the same characteristic symptoms, it seems clear that they can be included under one form, A'. Solani. These experiments show further that the virulence of R. Solani is very variable, as is also the degree of resistance of the vari- ous host plants, both depending on a number of varying factors. 360 BULLETIN No. 189 [June, TABLE 11. SUMMARY OF INOCULATION EXPERIMENTS Strain Original date of isolation Date of inoculation experiment Host Condition Per- centage of loss* Alfalfa 1910 1913 Alfalfa Seedlings 95 Alternanthera R.A.C. Alteruanthera R.A.F. Amaranthus 1912 1912 1913 1913 1913 1913 1913 1913 1914 1913 1914 1913 1914 1913 1914 1913 1914 1913 1913 1914 1914 Cabbage Carnation Clover Corn Tomato Alternanthera Carnation t > )> Alternanthera Carnation > > i > ) t Geranium A maranthus Plants Cuttings Seedlings > t Plants Cuttings > > Young plants Cuttings a Young plants Old plants > > > > (wounded) Cuttings 20 38 15 100 92 96 20 100 90 100 66 40 50 87 Aster 1913 1914 1914 1914 salicifolius Carnation 7 ) Aster Seedlings Cuttings Young plants Seedlings 100 100 16 29 Bean 1914 1914 Carnation Bean Cuttings Seedlings 23 5 Beet 1913 1913 1914 1914 Carnation t > Beet Cuttings j > Seedlings 65 100 ^0 Begonia 1911 1914 1914 1913 1913 Carnation Cuttings Young plants Old plants Cuttings 100 33 25 ion Carnation E.K 1911 1913 1913 Young plants Cuttings 6 90 Carnation R.O 1911 1913 1913 1913 1913 Young plants Old plants (wounded) Cuttings 85 100 o Carnation K.H. 1911 1913 1913 1913 Old plants > i (wounded) Cuttings 100 80 Carnation R.S 1911 1914 1914 1913 1913 1913 > ) Young plants Old plants (wounded) Cuttings 100 50 100 82 1913 1913 1913 Young plants Old (wounded) 93 50 100 In Experiments 1 and la the loss from plants wilted is not included in the percentage of loss. 1'JIG] PARASITIC RHIZOCTONIAS IN AMERICA 361 TABLE 11. Continued Strain Original date of isolation Date of inoculation experiment Host Condition Per- centage of loss" Carnation R.2 1912 1913 UaTnation buttings 100 1913 ) } Young planb 54 1913 > > Old plants 50 1913 i i 11 11 (wounded) 100 Carnation R.F 1912 1913 Beet Seedlings 98 1914 ) > i > 40 1913 Cabbage 40 1913 Carnation Cuttings 100 1914 j > 94 1913 Young plants 85 1913 j j j > 100 1914 1 1 11 50 1913 Old plants 1913 11 11 (wounded) 100 1913 Eggplant Seedlings 1913 Lettuce 1 1 60 1913 , > Plants 50 1913 Radish Seedlings 50 Carnation R.M.2 '1912 1913 Carnation Cuttings 96 1914 ; i ) i 43 1913 1 i Young plants 85 1913 ' ' Old plants 1913 1 i 11 11 (wounded) 50 1914 Carrot Seedlings 10 Carnation E 107 1912 1913 Alfalfa 11 70 1913 Beet Plants 100 1914 Cabbage Seedlings 75 1913 Carnation Cuttings 92 1914 i i 11 91 1913 11 Young plants 73 1913 i i Old plants 1913 i i 11 11 (wounded) 100 1913 > > Old plants 100 1913 Clover Seedlings 5 1913 Corn 11 Carnation R.F.2 1913 1914 Bean 11 3 1914 Carnation Cuttings 100 1914 . i i Y r oung plants- 66 Carnation R.121-5. . . 1912 1913 Cabbage Plants 70 1913 Tomato 11 20 Carnation (Sections 157 and 173) 1914 Bean 11 98 Carnation (Section 158) 1914 Beet 1 1 95 ( 163) 1914 Cabbage 1 1 90 '( 158) 1914 Carrot 11 10 ( 153) 1914 Corn Seedlings ( 170) 1914 Eggplant Plants ( 153) 1914 Lettuce 1 1 16 "See footnote, page 360. 362 BULLETIN No. 189 f June, TABLE 11. Continued Strain Original date of isolation Date of inoculation experiment Host. Condition Per- centage of loss" 1913 Beet Plants Cauliflower 1912 1913 1914 1913 1913 1913 1914 1913 1913 1913 Carnation > j > > > t > j Carrot Radish Turnip Cabbage Cuttings i } Young plants Old plants (wounded) Seedlings )> 66 30 13 5 98 50 98 Chenopodiuni 1913 1914 1913 1913 1914 1913 1914 1913 1913 1913 1914 ,, & > t Carnation > t Lettuce Tomato Alfalfa Plants Cuttings Young plants j > Old plants Seedlings Plants Seedlings 97 90 100 100 40 26 75 3 60 1912 1914 1913 Carnation Alfalfa Cuttings Seedlings 31 100 Coleus I 1912 1914 1913 1914 1913 1913 Carnation Clover > j Corn Carnation Cuttings Seedlings Cuttings 75 99 10 100 Coleus II 1913 1914 1913 1914 1914 1914 1914 j j > j Coleus > > Carnation Young plants Seedlings Cuttings i j 100 40 23 100 100 100 Corn 1912 1914 1914 1914 1913 Chrysanthemum Coleus ) > Alfalfa ) > Seedlings Cuttings Seedlings 100 70 100 g Cotton I 1911 1914 1913 1913 1914 1913 Carnation Clover Corn > > Cabbage Cuttings Seedlings > > >t Plants 51 2 50 Cotton II 1912 1913 1914 1913 1914 1914 1913 1913 Carnation y > ) > ) > Cotton Tomato Carnation Cuttings > > Young plants > ) Seedlings Plants Cuttings 100 62 87 56 100 100 Cotton III . 1912 1914 1913 1913 1913 1913 1914 > > Young plants Old plants t> (wounded) Old plants Cuttings 91 46 50 100 70 "See footnote, page 360. 1916] PARASITIC KIIIZOCTONIAS IN AMERICA 363 TABLE 11. Continued Strain Original date of isolation Date of inoculation experiment Host Condition Per- centage of loss* Cotton III 1912 1913 Carnation Young plants 28 1914 Cotton Seedlings 100 Dianthus barbatus g M 1913 1914 Carnation Cuttings 98 1913 > } Old pjants 75 1914 Dianthus barbatus Seedlings 50 Uiaiithusbarbatus N.P. 1913 1914 Carnation Cuttings 100 1914 Young plants 60 1914 Dianthus barbatus Seedlings 50 Diauthus plumarius. . 1913 1914 Carnation Cuttings 100 1913 > > Old plants 100 1914 Dianthus plumarius Seedlings 80 Dianthus sequeri 1913 1914 Carnation Cuttings 100 1914 Dianthus sequeri Seedlings 75 Kppnlant I 1912 1913 Carnation Cuttings 42" 1914 > i 93 1913 Young plants 60 1914 ) ) 20 1913 Old plants 1913 > > > > (wounded) 100 1913 Old plants 75 1913 Eggplant Seedlings 3 1914 ) i > > 4 1913 Lettuce > > 75 1913 Plants 20 Eggplant II 1913 1914 Carnation Cuttings 83 1914 Eggplant Seedlings 100 Lavatera 1913 1914 Carnation Cuttings 98 1914 ) ) Young plants- 36 1914 Lavatera trimestris Seedlings 95 Lettuce 1913 Carnation Cuttings 1914 j > i } 34 1913 i y Young plants 13 1913 > > Old plants 1913 ) > > > (wounded) 100 1913 Eggplant Seedlings 2 1913 Lettuce 90 1914 100 1913 Plants Poinsettia 1912 1913 Carnation Cuttings 75 1914 > > 52 1913 Old plants 1913 > > (wounded) 100 1914 Euphorbia variegata Seedlings 6 Potato E.P.C 1912 1913 Beet 50 1913 > > Plants 1913 Carnation Cuttings 90 1913 ft Young plants "See footnote, page 360. 364 BULLETIN Xo. 189 TABLE 11. Concluded Strain Original date of isolation Date of inoculation experiment Host Condition Per- centage of loss* Potato R.P.C 1912 1912 1912 1913 1912 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1913 1914 1913 1914 1914 1914 1914 1914 1913 1914 1913 1913 1914 1913 1913 1913 1914 1913 1913 1914 Radish Carnation j> > ; j > 5 5 55 ; > > > 5 ; 5 > ; 5 Beet Radish Turnip Carnation 5 5 Salvia splendens > > Carnation i 5 Amaranthus salicifolius Carnation 5 5 5 ! > 5 ' Clover Eggplant Lettuce Seedlings Cuttings Young plants Old plants > 5 55 (wounded) Cuttings Young plants Old plants 55 55 (wounded) Cuttings Old plants 55 55 (wounded) Old plants Plants Seedlings > } Cuttings . Young plants Seedlings Cuttings 7 ) Young plants Seedlings Cuttings 5 5 Young plants Cuttings 55 Young plants Old plants 55 ) 5 (wounded" Seedlings } 5 Plants .15 65 50 100 58 43 50 60 100 75 1 99 2 47 33 10 85 100 20 90 24 13 33 47 1 100 5 60 Potato R.P.I Potato R.P.O Potato R Sol Radish Salvia Sedum Sugar cane Thistle "See footnote, page 360. GROAVTII ON MEDIA In the course of these studies thirty-eight strains of Rhizoctonia were grown on five of the more common vegetable-extract agars and a solid synthetic medium. The composition of these media may be found in the appendix, together with a complete description of the growth of the various strains on them. 1916] PARASITIC RHIZOCTONIAS IN AMERICA 365 As a rule the fungus isolated from carnation plants, when grown on green-bean agar, produced a rapid-growing mycelium, which was practically all aerial, loose, and tufted. The most characteristic fea- ture was the production of concentric zones, tho this was not invaria- ble. Of the many hundred cultures made during the past three years from diseased carnation plants on green-bean agar, 90 percent have shown this zonation. This characteristic was influenced by neither light nor temperature. A typical growth on this medium is shown in Fig. 20, "Carnation R.H." A few of the carnation strains grown on the same medium and showing the same type of mycelium produced very indistinct zonation or none, as shown in Fig. 20, "Carnation R.F." Zonation persisted to some extent when the carnation strains were grown on other media than green-bean agar, but it was not so characteristic. The two strains from potato did not grow so rapidly nor quite so luxuriantly on green-bean agar as did the carnation strains, but they produced the same even, tufted, zonate growth. Here the zones were closer together. (See Fig. 20, "Potato R. Sol.") The growth of the strain from corn on green-bean agar was similar to that of "Potato R. Sol." The growth on green-bean agar of the strains from eggplant, let- tuce, Chenopodium, and thistle was different from any of the other forms in that the mycelium grew along the surface, running out ra- dially in strands, which became larger and more tufted at the edge. (See Fig. 21, "Eggplant I.") The strains isolated from alternanthera, coleus, salvia, and poin- settia, when grown on green-bean agar, showed the same even, fluffy to tufted growth. This was also characteristic of the strains from cauliflower, cotton, and sugar cane. Zonation in these strains was varied. (See Fig. 21.) The strain from onion when grown on this agar differed radi- cally from the others. The mycelium was bright colored, finer, and almost all submerged. (See Fig. 20.) The other strains studied on green-bean agar cannot be put in definite groups, as they shade into one another. However, the growth of the mycelium was somewhat similar in each case; practically the only difference noted was in the extent of the zonation. On corn-meal agar the growth of the strains was similar to a large extent ; the only great difference noted was in rapidity of growth. Zonation was very rare on this medium. The growth of the strains on oat agar was somewhat variable; zonation was sometimes present and sometimes absent. The most characteristic feature of the growth of the majority of the strains on potato agar was the turning brown of both the myce- lium and the medium. This same characteristic, but to a less degree, 366 BULLETIN No. 189 [June, FIG. 20. CULTURES OF RHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF MYCE- LIUM ON GREEN-BEAN AGAR (CULTURE 48 HOURS OLD). Top Row: (1) CAR- NATION R.H.; (2) CARNATION R.F. MIDDLE Row: (1) POTATO R. HOL.; (2) CARROT. BOTTOM Row: (1) CAULIFLOWER; (2) ONION 1016] PARASITIC RHizoctONlAS IN AMERICA 367 FIG. 21. CULTURES OF BHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF MYCE- LIUM ON GREEN -BE AN AGAR (CULTURE 48 HOURS OLD). TOP Bow: (1) ALTER - NANTHERA'B.A.F.; (2) ALTERNANTHERA B.A.C. MIDDLE Bow: (1) POIN- SETTIA; (2) COLEUS I. BOTTOM Bow: (].)- EGGPLANT I; (2) LETTUCE 368 BULLETIN No. 189 f June, FIG. 22. CULTURES OF EHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF SCLERO- TIA: (1) ALTERNANTHERA R.A.C.; (2) SALVIA; (3) POINSETTIA; (4) ALTER- NANTHERA E.A.F. ; (5) COLEUS ; (6) EGGPLANT II; (7) EGGPLANT I; (8) LETTUCE; (9) CHENOPODIUM; (10) THISTLE; (11) CARNATION E.F.2; (12) CARNATION E.S.; (13) CARNATION E.2; (14) CARNATION E.H.; (15) CARNA- TION E.G.; (16) ASTER; (17) COTTON I; (18) BEET; (19). CARROT; (20) BEAN 1916] PARASITIC RHIZOCTONIAS IN AMERICA 369 FIG. 23. CULTURES OF RHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF SCLEHO- TIA: (1) AMARANTHUS; (2) PANSY; (3) LAVATERA; (4) SWEET ALYSSUM; (5) LOBELIA; (6) ALFALFA; (7) CLOVER; (8) CORN; (9) CAULIFLOWER; (10) SUGAR CANE; (11) BUCKWHEAT; (12) RED CLOVER; (13) SEDUM; (14) GYPSOPHILA; (15) ONION; (16) DIANTHUS BARBATUS S.M. : (17) DIANTHUS PLUMARIUS; (18) DIANTHUS SEQUERI; (19) DIANTHUS BARBATUS N.P.; (20) ASTER (CARNATION STRAIN) 370 BULLETIN No. 189 [June, was found with the growth on potato-glucose agar. On both these media zonation was usually lacking or indistinct. On Agar XII most of the strains grew rather poorly and produced a white, flaky growth, with varying zonation. Early in the study of the characters of the strains on culture media, it was noticed that as there were characteristic differences in growth, so also were there differences in the production of sclerotia. The strains "Eggplant I," "Lettuce," " Chenopodium, " and "Thistle" on green-bean agar all formed sclerotia in a characteristic manner. The sclerotia were white at first and flat, later turning black, and as the culture became older, curling up and becoming crust-like. All four of the forms mentioned above showed these same character- istics, altho they were originally obtained from widely separated locali- ties. (See Fig. 22.) The strain from onion produced sclerotia which were entirely different from those of other strains in that they were small (.5 to 1 millimeter in diamater), perfectly round, bright colored, and developed submerged in the medium. (See Fig. 23.) The strains "Buckwheat," "Carnation R.O.," " Gypsophila, " and "Sedum" rarely produced sclerotia in culture. Repeated observations showed that this loss of power to produce sclerotia was the first sign of the de- generation and loss of virulence of the strain. All the other strains studied produced sclerotia which were at first white, later becoming brown. Altho the sclerotia from the strain from potato are similar to those from carnation when grown on culture media, on the potato tuber they are entirely different. For the most part the Rhizoctonia sclerotia on potato tubers which the writer has examined are flat and hard, have a black luster, and are in many re- spects like the sclerotia produced in culture media by the strains from eggplant, lettuce, etc. The only conclusion that can be drawn from this study of the growth of Rhizoctonia Solani on media is that the strains are very variable, those from the same host often producing a different growth, even; on the same media, and- that the differences in various cultural characters which are shown by strains from different hosts are no greater than differences which may be manifested by two different strains isolated from the same host or by the same strain at different ages. MEASUREMENT OF MYCELIAL CELLS It was rather difficult to choose a standard in the measurement of the mycelial cells, because the cells varied in size at different ages and on different media. Finally the following standard was chosen: Hyphae from the outer edge of a twenty-four hour old culture on green-bean agar were selected at random. The length and width of a cell from which the branch arose nearest the tip of the hypha, and 1916] PARASITIC RHIZOCTONIAS IN AMERICA 371 the distance on the inner side from the parent hypha to the first sep- tum of the branch, were measured. Ten cells of each strain were measured, and the averages of these measurements used for compari- son. As shown in Table 12, the measurements varied considerably, and this was true even with strains from the same host. In the three car- nation strains measured, the length of the mycelial cells varied from TOfji. to 181. 1^, a difference of 111.7/x. However, the average of ten measurements brings the difference down to some extent. A still more striking difference was noted in the strains from Dianthus, where the smallest reading was 50//, and the largest 215/*, a difference of 165/A. Similar differences were also found in comparing the two other meas- urements. In all cases, altho the table does not bring out this point, different measurements of the cells of the various strains overlapped. For ex- TABLE 12. MEASUREMENTS OF MYCEIJAL CELLS OP EHIZOCTONIA Strain Length of cell Width of cell Distance from cell to septum of branch Alfalfa u 152.04 H 5.76 V. 10.08 Alternanthera R.A.C 113.40 3.92 6.72 " B A F 124.60 4.94 9.32 107.80 4.83 7.98 180.04 6.57 13.08 Beet 77.92 4.34 6.52 Carnation R H 116.09 4.59 10.83 ' ' R.M.2 141.40 5.60 10.49 ' > E.F.2 128.15 5.19 10.92 Carrot 116.64 4.42 9.60 Cauliflower 119.64 4.20 9.60 Chenopodium 175.56 5.43 11.20 Clover 88.20 5.32 8.53 Coleus I 117.60 5.04 10.21 Coleus II 133.28 4.97 10.22 Corn 101 64 4.39 9.24 Cotton I 65.24 5.50 10.18 Dianthus barbatus S.M N.P 113.12 161.00 5.58 5.27 9.44 10.58 sequeri 131.60 6.29 6.44 plumarius . . 166 95 5.65 13.44 Eggplant I 13234 4.20 11.65 " II 148 88 5.60 9.57 Gypsophila repens 122 08 3.55 8.03 Lavatera 91 84 5 89 9 18 Lettuce 119 92 439 10 54 Poinsettia 126 20 3.44 7.92 Salvia 111 16 5 01 9 93 Sedum 90 80 4 48 7 00 Sugar cane 113 12 409 657 Sweet pea 13048 5 04 854 Thistle 138.08 4.62 11.48 372 BULLETIN No. 189 [June, ample, while the average length of a cell from "Cotton I" was only 65/t, the largest reading was 127. .V, which was higher than the small- est measurement of a cell of the strain " Chenopodium, " whose aver- age reading was 110/u higher than that of "Cotton I." If measure- ments are made of hyphae forty-eight hours old, the differences are still more striking, even in the same strain. Hence, on the measurement of mycelial cells of Rhizoctonia Solani, as on the study of the growth on media, no conclusions can be based in regard to distinguishing the strains of this difficult species. SOIL SURVEY OF RHIZOCTONIA As shown in Table 1, Rhizoctonia Solani has been observed in al- most every state in the Union, and causes injury to a large number of plants under various conditions and in widely different types of soils. To determine to how great an extent Rhizoctonia is actually present in the soil, several surveys were made at the University of Illinois in fields containing a variety of plants. Survey of ihe Perennial Garden, Horticultural Grounds, April 28 to May 1, 1914. During the summer and fall of 1913, Rhizoctonia was isolated from a number of perennial plants in the garden. To determine whether the fungus lived on the dead parts of the plants or in the soil or both during the winter season, a survey was made the following spring. Since it is somewhat difficult to isolate Rhizoctonia directly from the soil by means of soil cultures, the following method was devised to determine its presence in the soil: Small patches of ground were selected over the field about twenty feet apart, so that the results might give a fair idea of the distribution of the fungus. Each space was cleared except for a small living plant, and the soil thoroly watered. Three sheets of moistened filter paper were then placed on the ground over the plant. To prevent evaporation, a small flat with a layer of wet moss attached to the bottom was placed over the paper. The flats had previously been sterilized in formalin (1-100) and the moss sterilized in the autoclave. Thru several small holes in the bot- tom of the flat, water was added to the moss from day to day to keep it moist. At the end of the fifth day the plant parts were removed to the laboratory. The presence of the fungus was determined by means of pure cul- tures and by microscopic observation. Where the identification de- pended solely on microscopic observations, the material was left in a covered dish for several days until the strands of the fungus became older, when they could be distinguished more readily by their color. In thirteen cases out of sixteen Rhizoctonia was found present on the dead or living pieces of plants placed in contact with the soil; PARASITIC RHIZOCTONIAS IN AMERICA 373 1 1 - o _r o> , TJ X -M CS >_, CS 3 * S3 * e ?3 -13 0} 5 s " n njj o ^~ CS " O H g 0>-S 2 > S M - S ^- Qi QJ ^H O *"* C . - " I O '^ T* flflM-C w " --'S 2 !-2 'E ^, i ^ ' -C ^3 H , en *; ^J C 15! CS '5 0.2 .5 ^* OJ ^ M 4J O3 5 374 BULLETIN No. 189 hence we may conclude that this fungus was very abundant both in the soil and on the plant parts in contact with the soil. Survey of Plot Used for Field Inoculation Experiments, May 6 to May 11, 1914. This plot, formerly used by the Agronomy Depart- ment, had been under cultivation for a number of years. The pre- vious season the field had been in potatoes and corn. The old potato stalks were left scattered over the field during the winter. A survey of the plot was made before plowing, following the same method as was used as in the preceding experiment. Sixteen flats were set out twenty-five feet apart. After five days an examination for the presence of Rhizoctonia was made. By microscopic examination and pure cultures, Rhizoctonia was detected in ten trials out of sixteen on this plot. Survey of Agronomy Plots on North Farm, September 26 to Octo- ber 2, 1914. Here a more extensive survey was conducted. The agronomy plots on the North Farm were chosen for this purpose be- cause of the fact that they had been under continuous cultivation since 1895, and showed the effects of different methods of soil treat- ment, various systems of crop rotation, and the application of differ- ent kinds of food. (For treatments and rotations used, see Fig. 24.) These plots are also typical of the prairie soil, which represents the most extensive and important type of soil in Illinois. The procedure followed in this survey was modified as follows: In stead of a flat, a seven-inch flower pot, which could be easily steri- lized and dried, was employed. Small cheesecloth bags were filled with sphagnum moss ; these were sterilized in the autoclave. When ready for use, the bags were moistened and placed in the bottom of the pots and secured in such a way that they remained in position when the pots were inverted. A small patch of soil, one in each plat, was lev- eled off, only a small living plant or some plant debris being left. Several thicknesses of moistened filter paper were then laid over the spot, and a flower pot was placed over the whole. The pot was pushed into the ground about three inches and the soil heaped up around it on the outside. The pots were left in this condition about one week, during which time the moss was moistened at intervals. Conditions were very favorable to the growth of Rhizoctonia if it was present in the soil. When the pots were lifted, the plant parts or debris with some of the soil were wrapped in the filter paper and placed under bell jars. The contents of the papers were then examined for the presence of Rhizoctonia. These plots showing the effects of diverse treatments yielded R. Solani in sixty-four trials out of seventy. The six negative results were scattered over the field, so that no correlation between the treat- ment of the plot and the presence of Rhizoctonia can be said to exist, 1916] PARASITIC BHIZOCTONIAS IN AMERICA 375 The results of these experiments admit of no question as to the presence of the fungus Khizoctonia Solani in the soil in the vicinity of Urbana. PARASITISM OF RHIZOCTONIA SOLANI KUHN That R. Solani is an active parasite under certain conditions would never be questioned by anyone who had seen a severe attack of car- nation stem rot in the field or greenhouse. In the cutting bench this fungus causes damping-off of cuttings in an incredibly short time, while seedlings damp oft' almost as fast. At times Rhizoctonia causes considerable loss in potato fields. In fact, it may become epidemic and cause serious injury to most of the field, vegetable, and floricul- tural crops. The epidemics are apparently due to a combination of factors, such as the presence of a virulent strain of the fungus, a susceptible variety of plant, and optimum conditions of temperature and moisture for infection and development. Under ordinary conditions most of the strains appear to be weak parasites. The apparently universal presence of Rhizoctonia in the soil, where it can live indefinitely on dead organic matter under ordinary conditions, makes it a dangerous fungus. The fact that it shows no marked specialization and can attack a large variety of weeds assists in harboring the fungus and in keeping up its virulence. The sclero- tia and mycelium can live under adverse conditions for several years. Transfers from soil cultures started in December, 1911, kept in the laboratory, and allowed to dry out, yielded pure cultures as late as July, 1914. Soil cultures left in the field during the entire winter yielded the fungus in the spring. In all but one of the experiments inoculation was brought about without wounding the plants in any way, in many cases the fungus being simply mixed with the soil in which the plants were growing. The results furnish convincing proof of the parasitism of the fungus. The conditions under which all strains manifested their greatest para- sitism were primarily a high temperature (above 88 F.) and a soil moisture content either too low or too high for the best development of the plant. When carnation plants growing in soil inoculated with Rhizoctonia were given a heavy watering and the soil was then allowed to dry out, they were killed more rapidly than plants growing under the same conditions but in continually over-watered soil. Plants watered normally died off slowly and the percentage of loss was very much less. Repeated observations in greenhouse and field have shown that a certain amount of the mycelium must be present before the fungus is able to attack and kill the plant. A small amount of mycelium has always been observed around a carnation plant in the bench a week 376 BULLETIN No. 189 [June, or more before the plant showed any signs of being diseased. In fact, a certain amount of mycelium is always present in the carnation soil in the greenhouse, but it is only when the temperature is high that the fungus is able to attack the plants. This explains why stem rot of carnations is more severe during the summer months than in the winter. (See Experiment 6, page 349.) In the field similar conditions are necessary to result in infection of a plant. Investigations to determine how much vigor the mycelium must attain before the fungus can attack a plant are now in progress, as is also a histological and enzymatic study. SUMMARY 1. At the present time there are recognized in America two species of truly parasitic Rhizoctonias : The common form, RMzoctonia Solani Kiihn (Corticium vagum B. & C.), widely distributed and oc- curring on a great number of hosts; and R. Crocorum (Pers.) DC., with a limited distribution on alfalfa and potato tubers. A third RMzoctonia, Corticium ochraleucum (Noack) Burt, is found on the leaves of pomaceous fruit trees, while a fourth species isolated from damped-off onion seedlings is of questionable parasitism. 2. The plants thus far listed as more or less subject to attacks of RMzoctonia Solani Kiihn in the United States number about 165 species. All the more important families of dicotyledons are included in this list, as well as a number of monocotyledons, several gymno- sperms, and Equisetum. Most of the Agricultural plants, vegetable and field crops, herbaceous plants, and many weeds are susceptible to attacks of this fungus. 3. The symptoms produced by Rhizoctonia Solani Kiihn in nat- ural infection are largely similar when appearing on the same type of host. The damping-off of seedlings and cuttings of various plants is identical, as is the rotting of a number of root crops. In most her- baceous plants a stem rot is produced, the symptoms of which are also identical on the various hosts. On very resistant plants lesions only are formed ; these are apparently the same on the different hosts. 4. From these inoculation experiments with a large number of different types of plants, we must conclude that all the strains studied, which were obtained from a wide range of hosts of diverse geographi- cal origin, can attack the same species of plant and produce the same characteristic symptoms. No marked specialization was noted in any of the strains. Thus all the strains studied can be included under one form, Rhizoctonia Solani Kiihn. The inoculation experiments show further that the virulence of R. Solani is very variable, as is also the degree of resistance of the various host plants, both depending on a number of varying factors. 1916] PARASITIC KHIZOCTONIAS IN AMERICA 377 5. Studies of the growth of Rliizoctonia Solani Kiihn on media show that the strains are very variable, those from the same host often producing a different growth even on -the same media, and that the differences in various cultural characters which are shown by strains from unlike hosts are no greater than the differences which may be manifested by two different strains isolated from the same host or by the same strain at different ages. 6. Measurements of mycelial cells of Rhizoctonia Solani Kiihn showed such large variations, not only between strains from different hosts but also between different strains from the same host, that no standard could be determined on for distinguishing the different strains. 7. By means of a local soil survey, it was found that RJiizoctonia Solani Kiihn is abundant in cultivated land, where it may live either on dead organic matter in the soil or on weeds and other plants. 8. A certain vigor of mycelium must be attained before Rliizoc- tonia Solani Kiihn is able to attack a plant. A high temperature (88 F.), together with either too little or too much moisture, deter- mines to a large degree the virulence of the strains. It is only under certain conditions that the fungus becomes a dangerous parasite. The writer gratefully acknowledges his indebtedness to Dr. F. L. Stevens, Professor of Plant Pathology, and to Dr. J. T. Barrett, for- mer Chief Assistant in Botany, for their kind assistance and encour- agement. He wishes also to thank Professor H. B. Dorner, Assistant Chief in Floriculture ; Mr. C. C. Rccs, formerly Assistant in Floricul- tural Pathology; and other members of the Division of Floriculture for assistance rendered during the progress of this work. 378 BULLETIN No. 189 [June, APPENDIX COMPOSITION OF MEDIA USED IN EXPERIMENTS Corn-Meal Agar (Shear*). To 4 teaspoonfuls of corn meal add 1 liter of dis- tilled water. Keep in water bath for one hour at a temperature below 60C. Strain thru gauze, and to the filtrate add 1 percent agar flour. Steam three-quarters of an hour. Filter thru paper tube and place in autoclave for 15 minutes at 115 C. Green-Bean Agar. 300 grams young string beans cooked in 500 cc water for one hour and strained thru cloth. 15 grams agar (powdered) melted in 500 cc. water. Mix the two, add enough water to make 1000 cc., add 6 to 8 grains egg albumen, and boil in autoclave. Filter thru cotton. Oat Agar (Clinto^). 200 grams oats ground fine thru a coffee mill and soaked in 500 cc. water for one hour. 15 grams agar melted in 500 cc. water and strained thru cheesecloth. Mix the two but do not filter, since the most nutrient part of the medium would be lost. Potato Agar. 300 grams peeled potatoes, sliced as thin as possible and cooked in 500 cc. water for one hour. Strain thru cloth. 15 grams agar (powdered) melted in 500 cc. water. Mix the two and add enough water to make 1000 cc. Add 6 to 8 grams egg albumen (powdered) and boil in autoclave for a short time. Filter thru cotton. Potato-Glucose Agar. 290 grams peeled potatoes, sliced as thin as possible and cooked in 500 cc. water for one hour. Strain thru cloth and add 20 grams of glucose. 15 grams agar (powdered) melted in 500 cc. water. Mix the two, add enough water to make 1000 cc., add 6 to 8 grams egg albumen (powdered), and boil in autoclave for short time. Filter thru cotton. Agar (Cook c ) Water 1000.00 cc. ims Aear 15.00 grf Glucose 20.00 Ammonium nitrate 1.00 Potassium nitrate 1.00 Ammonium sulfate 1.00 Magnesium sulfate 25 Dipotassium phosphate 25 Calcium chlorid". . .01 GROWTH ON MEDIA ' ' ALFALFA ' ' On Corn-Meal Agar. Growth poor and rather slow. Mycelium white, fine, submerged, and scarcely visible. No coloring of the medium. No zonation. On Green-Bean Agar. Growth poor and slow. Mycelium white, fine, loose, and becoming somewhat tufted. Zonation. Like strain from corn. On Potato Agar. Growth rather slow. Characterized by the dark color of the mycelium and the turning of the medium to a darker color. Hyphsu loose, fine, and practically all submerged. No zonation. U. S. Dept. Agr., Bur. Plant Indus., Bui. 252, 15. 1913. b Conn. Sta. Rpt. (1909-10), 32, 760. 1911. c Del. Sta. Bui. 91, 12. 1911. d Omitted from formula used. 1916] PARASITIC BHIZOCTONIAS IN AMERICA 379 Stewart, 1 " 5 in reporting the damping-off of alfalfa seedlings in the greenhouse and the crown rot of mature plants in the field, states that "the one causing dampiner-off of seedlings in the greenhouse is different from the one found in the field. When grown on potato agar (slightly acid, neutral, or slightly alkaline), the former produces a conspicuous dark brown discoloration of the medium, whereas the latter discolors it only slightly. This character may be useful in the identi- fication of the damping-off Rhizoctonia. Such discoloration of the medium is not common among the species of Ehizoctonia. " It is interesting to note that the strain obtained from Louisiana causing a damping-off of alfalfa seedlings and a number of other strains showed the same discoloration as the one studied by Stewart. On Agar XII. Growth fair. Few loose, erect hyphse, becoming denser and finally forming an indistinct zone. " ALTERNANTHERA B. A. C." On Corn-Meal Agar. Growth very rapid, but not dense. Mycelium white, loose, aerial, and fine. No zonation. On Green-Bean Agar. Growth good. Mycelium tufted and compact, not turning darker. Zonation somewhat distinct at end of third day. Three zones present. On Oat Aoor. Growth rapid. Mycelium flat, and very compact, forming a mat over the surface. Zonation. On, Potato Agar. Growth very rapid, with zone formation beginning im- mediately. Mycelium all aerial and growing very compactly. Plate was covered at end of forty-eight Lours and showed two distinct zones and one indistinct. On Potato-Glucose Agar. Growth rapid; plate covered in forty-eight hours. Mycelium white, loose, and flaky. Zonation. On Agar XII. Growth good. Mycelium white, fine, compact, and somewhat flaky. Zonation. . ' ' ALTERNANTHERA E. A. F. ' ' On the various media this strain produced the same kind of growth in each case as the strain from the cutting bench, except that it grew more rapidly. ' ' ASTER ' ' On Green-Bean Agar. Growth fair. Mycelium white, loose, regular, :oid flat, becoming somewhat tufted. Four zones formed at end of the fourth day. On Oat Jf/er. Growth fair. Mycelium white, loose, flat, and regular, be- coming fluffy and tufted. Like strain ' ' Carnation E. F. " Five zones at end of fourth day. On Potato-Glucose Agar. Growth slow and poor. Mycelium mostly submerged and turning brown. No zonation. On Agar XII. Growth fair. Mycelium white, loose, flat, and regular, be- coming somewhat tufted. Zonation. "BEAN" On Corn-Meal Agar. Growth very poor; scarcely visible. Mycelium white, fine, somewhat aerial. No zonation. On Grcen-'Bean Agar. Growth slow. Mycelium fine, aerial, loose, and white, darkening with age. Two zones formed, but not very distinct; otherwise like the strain from carrot. On Potato Agar. Growth fair. Mycelium fine, more or less submerged, and discoloring the medium only slightly. No zonation. 380 BULLETIN No. 189 [June, On Agar XII. Growth rapid. Mycelium somewhat tufted and dense. Three distinct zones present. "BEET" On Green-Bean Agar. Growth good. Mycelium flat and compact. Several Hones present. ' ' BEGONIA ' ' On Corn-Meol Agar. Growth fair. Mycelium rather compact and white. No zonation. On Green-Bean Agar. Growth fair. Mycelium white, tufted, and compact. Zonation indistinct. On Potato Agar. Growth fair. Mycelium compact, dense, and white; me- dium turning dark. Zonation. On Agar XII. Growth scant. Mycelium white, fine, and loose. No zonation. ' ' CARNATION U.K." On Corn-Meal Agar. Growth good. Mycelium white, making a rather dense growth for corn-meal agar. Zonation indistinct. On Green-Bean Agar. Growth good. Like strain "Carnation R. H. " On Oat Avar Growth good. Mycelium white, loose, edge tufted. Zonation. On Potato Agar. Growth poor. Mycelium loo?e and scattering, medium turn- ing darker. Zonation indistinct. On Agar XII. Growth poor. Mycelium white, loose, and scattered; edge irregular. Zonation indistinct. "CARNATION B. H." On Corn-Meal Aaar. Growth fair. Mycelium white, fine, and in loose strands ; rather dense at center. No zonation. On Grccn-Bcan Agar. Growth good. Mycelium dark at center, loose, and tufted; edge irregular. Zonation very characteristic of the strains isolated from diseased carnation plants. On Potato Agar. Growth poor. Mycelium fine and scattered; edge irregular. Mycelium causing a characteristic browning of the medium. Zonation indistinct. On Agar XII. Growth poor. Mycelium white, fine, loose, and scattered. No zonation. "CARNATION E. S." On Corn-Meal Agar. Growth fair. Mycelium white, fine, but rather dense at center; edge regular. Zonation. On Green-Bean Agar. Growth good. Mycelium loose, white, and tufted; edge regular. Later, mycelium turned brown. Zonation somewhat indistinct. On Potato Af;ar. Growth poor and scant. Mycelium producing a distinct browning of the agar. Zones indistinct. On Agar XII. Growth poor. Mycelium white, scant, loose, and flat. Zonation. ' ' CARNATION E. F. " On Corn-Meal Agar. Growth good. Mycelium white, loose, and somewhat tufted. No zonatiou. On Green-Bean Agar. Growth fair. Mycelium white, compact, and tufted. Zonation somewhat indistinct. 1916] PARASITIC RHIZOCTONIAS IN AMERICA 381 On Oat Agar. Growth good. Mycelium white, loose, flat, and fairly dense; edge tufted. Zonal ion. On Potato Agar. Growth poor. Mycelium scant, like that produced by strains from carnation. On Potato-Glucose Agar. Growth poor. Mycelium white, loose, scattered, and somewhat flaky ; edge very irregular. Zonation. On. Agar XII. Growth poor. Mycelium white, fine, loose, flat, and scatter- ing; edge very irregular. Zonation indistinct. ' ' CARNATION R.M.2 ' ' On Corn Meal Agar. Growth good. Mycelium white, tufted, and somewhat compact. No zonation. On Green-Bean Agar. Growth fair. Mycelium white, tufted, ard compact. Zonation indistinct. On Oat Agar. Growth fair. Mycelium white, loose, and somewhat flaky at center; edge loose and irregular. Zonation. On Potato Agar. Growth poor. Mycelium loose and fine. Zonation indis- tinct. On Potato-Glucose Agar. Growth fair. Mycelium brown, loose, und flat; edge loose and tufted. No zonation. On Agar XII. Growth fair. Mycelium white, loose, flat, and scattered. No zonation. "CARNATION B.D.C." On Corn-Meal Agar. Growth good. Mycelium white, loose, tufted, and rather dense. No Donation. On Green Tican Agar. Growth good. Mycelium white, loose, tufted, and dense. Zonation distinct. On Oat Agar. Growth fair. Mycelium white, somewhat dense at center, and more tufted at edge. Zonation. On Potato Agar. Growth poor. Mycelium loose and flat, darkening slowly with age. Zoi.ation indistinct. On Potato-Glucose Agar. Growth fair. Mycelium white, flat, and flaky at center.; edge loose and fluffy. Zones numerous and distinct. On Agar XII. Growth poor. Mycelium white, somewhat flaky at center; edge irregular an-1 scattered. Zonation. ' ' CARROT ' ' O.i Corn-Meal Agai. Growth good. Mycelium white, fine, and somewhat com- pact. No zonation. On Green-Bean Agar. Growth poor. Mycelium loose, flat, and somewhat fluffy; white at first, followed by purplish tinge. Zonation not very distinct. On Oat Agar. Growth fair. Mycelium white, fine, loose, and flat. Zonation indistinct. On Potato Agar. Growth fair. Mycelium dark, dense, and compact. Zona- tion indistinct. On Potato-Glucose Agar. Growth fair. Mycelium dark, loose, flat, and flaky. Four to six zones present. On Agar XII. Growth slow. Mycelium white, loose, and somewhat flaky. Zonation. 382 BULLETIN No. 189 [June, 1 ' CAULIFLOWER ' ' On Corn Meal Agar. Growth poor. Mycelium white, loose, and scant. No zonation. On Green-Sean Agar. Growth good. Mycelium white, tufted, and compact; edge regular. Zonatioii. On Oat Agar. Growth good. Mycelium white, fine, loose, flat, and dense, running out in characteristic strands. No zonation. On Potato-Glucose Agar. Growth fair. Mycelium dark, loose, flat, and flaky. One zone at outer edge. On Agar XII. Growth good. Mycelium white, loose, flat, and flaky. Zonation. " CHENOPODIUM " On Green-Bean Agar. Growth good. Mycelium white, flat, radial, and com- pact. No zonation. "CLOVER (RED)" On Green-Bean Agar. Growth good. Mycelium flat and compact. Zonation. "COLEUS I" On Corn- Meal A gar. Growth good. Mycelium white, loose, and somewhat compact. No zonal iou. On Green-Bean Agar. Growth good. Mycelium white, tufted, and compact. Zonation indistinct. On Oat Agar. Growth good. Mycelium white, loose, and flat; edge fluffy. No zonation. On Potato Agar. Growth fair. Mycelium loose and tufted, turning darker with age. No zonation. On Potato-Glucose Agar. Growth fair. Mycelium dark, loose, and flaky; edge irregular. Zonation. On Agar XII. Growth good. Mycelium loose, dense, and white. No zonation. ' ' CORN ' ' On Corn-Meal Agar. Growth poor. Mycelium white, fine, and scattered. No zonation. On Green-Bean Agar. Growth fair. Mycelium loose at edge and somewhat compact, turning darker with purplish tinge. Two distinct zones. On Potato Agar, Growth fair. Mycelium dense and compact. Mycelium and medium turned dark. Zonation indistinct. On Agar XII. Growth fair. Mycelium white, loose, tufted, and rather dense at center. Zonation. "COTTON I" On Green-Bean Agar. Growth fair. Mycelium loose, tufted, dense, and white. Two zones present. . On Oat Agar. Growth good. Mycelium white, loose, flat, dense, and radial, later taking on a wrinkled appearance. No zonation. On Potato-Glucose Agar. Growth fair. Mycelium white, flat, dense, flaky, and regular; loose at edge. Zonation indistinct. 1916] PARASITIC EHIZOCTONIAS IN AMERICA 383 On Agar XII. Growth fair. Mycelium flat, somewhat dense, flaky, and white at center; edge loose. Two distinct zones. "COTTON II" On Green-Bean Agar. Growth fair. Mycelium loose, tufted, and fairly dense, later turning brown. Two zones present. On Oat Agar. Growth fair. Mycelium white, fine, loose, and flat, forming a mat over surface of the medium. One zone present. On Potato-Glucose Agar. Growth fair. Mycelium loose, flat, and fairly dense ; edge irregular. Later both mycelium and medium turned brown. Two zones present. On Agar XII. Growth fair. Mycelium white, loose, and somewhat tufted. Three zones present. "DlANTHUS BARBATUS N.P. " On Green-Bean Agar. Growth fair. Mycelium tufted and compact. Zonation indistinct. "DlANTHUS BARBATUS S.M. " On Green-Bean Agar. Growth good. Mycelium tufted and compact. Zona- tion rather indistinct. ' ' DlANTHUS PLUMARIUS ' ' On Green-Bean Agar. Growth good. Mycelium loose, white, and somewhat tufted; edge regular. Zonation characteristic of the carnation strains. "DlANTHUS SEQUERl" On Green-Bean Agar. Growth good. Mycelium loose, white, and somewnut fluffy; edge regular. Zonation characteristic of carnation strains in all respects. ' ' EGGPLANT I ' ' On Corn-Meal Agar. Growth poor. Mycelium white, fine, and mostly sub- merged. No zonation. On Green-Bean Agar. Growth good. Mycelium white, flat, radial, compact, and dense. One zone at center. On Oat Agar. Growth fair. Mycelium white, loose, flat, interwoven, and somewhat tufted. Zonation. On Potato Agar. Growth good. Mycelium dark, compact, dense, and radial. No zonation. On Potato-Glucose Agar. Growth fair. Mycelium in radial strands, flat, and white. No zonation. On Agar XII. Growth fair. Mycelium white, flat, dense, and compact. One zone present. ' ' GYPSOPHILA ' ' On Green-Bean Agar. Growth fair. Mycelium white, fluffy, and somewhat compact. Zonation very characteristic of strains from carnation. ' ' LAVATERA ' ' On Green-Bean Agar. Growth good. Mycelium white, loose, and tufted; edge even. Several zones present. 384 BULLETIN No. 189 [June, "LETTUCE" On Corn-Meal Agar. Growth fair. Mycelium white, fine, slightly aerial, az