THE UNIVERSITY 
 
 OF ILLINOIS 
 
 LIBRARY 
 
 650.7 
 II6b 
 
 cop-eL 
 
 A6RIGULTUBAL 
 UIBABY 
 
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UNIVERSITY OF ILLINOIS 
 
 Agricultural Experiment Station 
 
 BULLETIN No. 229 
 
 DENDROPHOMA LEAF BLIGHT OF STRAWBERRY 
 
 BY H. W. ANDEHSON 
 
CONTENTS OF BULLETIN No. 229 
 
 PAGE 
 
 INTRODUCTION 127 
 
 SYMPTOMS 127 
 
 ISOLATION AND CULTURAL CHARACTERS 129 
 
 MORPHOLOGY AND LIFE HISTORY 129 
 
 Mycelium 129 
 
 Pycnidia 129 
 
 Spores 131 
 
 Conidiophores 131 
 
 INFECTION EXPERIMENTS 131 
 
 HISTORY OF THE DISEASE 132 
 
 TAXONOMY OF THE FUNGUS 134 
 
 OTHER LEAF-INHABITING FUNGI OF THE STRAWBERRY 135 
 
 CONTROL MEASURES . 135 
 
DENDROPHOMA LEAF BLIGHT OF STRAWBERRY 
 
 BY H. W. ANDEKSON, ASSISTANT CHIEF IN POMOLOGY 
 
 INTRODUCTION 
 
 During the summer of 1919 a serious leaf blight of strawberry 
 was observed in several localities in Illinois and Indiana. At first it 
 was regarded as an advanced stage of the ordinary leaf spot caused 
 by Mycosphaerella Fragariae (Sehw.) Lind., but a closer examination 
 showed that even from the inception of the attack it had entirely 
 different symptoms. A more detailed study revealed the presence 
 of fungus fruiting bodies quite distinct from those of the leaf spot. 
 The destructive nature of the disease and its apparently wide dis- 
 tribution seemed to warrant a more extensive study. The results of 
 this investigation are given in the following pages. 
 
 SYMPTOMS 
 
 The lesions of leaf blight, even in an early stage, are much larger 
 than the mature lesions of the ordinary leaf spot. Usually, only one 
 spot appears on a leaflet, tho there may be from two to five. In an 
 advanced stage the most common condition is a V-shaped dead area 
 extending from the midrib or one of the larger veins to the tip or 
 side of the leaflet with the apex of the V pointing inward. 
 
 The young spots are uniformly reddish-purple when they first 
 appear and are almost circular in outline. As they enlarge the cen- 
 tral area dies and becomes brown. Later, three zones may be ob- 
 served (Fig. 1) : (1) an outer purple zone about 2-3 mm. broad, 
 which gradually shades off into the normal green of the leaf; (2) 
 a light brown zone about 5 mm. broad; and (3) a central dark brown 
 area 2-3 mm. in diameter which is sometimes covered with a white 
 granular layer. 
 
 On the under surface of the leaf the symptoms are the same ex- 
 cept that the hairy covering masks the colors and makes 'them ap- 
 pear lighter and less sharply defined. 
 
 When the spots occur between prominent veins they usually re- 
 main circular in outline until they are 1-2 cm. in diameter. If they 
 occur on a prominent vein, and especially if on the midrib, they 
 elongate rapidly and become elliptical in outline. The leaf area be- 
 tween the lesion and the edge of the leaflet becomes streaked with 
 purple, the color being especially deep along the veins. Since the 
 veins extend in a fan-like manner from the point of infection, the 
 resulting lesion is the characteristic V-shaped discolored area de- 
 scribed above. This area of leaf tissue remains alive for some time 
 after it shows the purple discoloration but finally dies. 
 
 127 
 
128 
 
 BULLETIN No. 229 
 
 [July, 
 
 FIG. 1. STRAWBERRY LEAF BLIGHT SHOWING VARIOUS TYPES OF LESIONS 
 The leaflet in the upper left-hand corner shows a typical fan-shaped dead 
 
 When the spots are a centimeter or more in diameter, small black 
 dots, the pycnidia, appear scattered over the central dark brown area 
 and to a certain extent in the lighter brown zone outside of this. 
 These dots are present on both surfaces of the leaflet but are more 
 evident on the upper. In some cases the pycnidia do not appear un- 
 til a large area of the leaflet is dead. 
 
 In 1919, the diseased areas were evident as early as the first of 
 June, but it is not known how much earlier they may appear. They 
 are more often observed on the older leaves but are not uncommon 
 on young, vigorous leaves. The spots continue to appear thruout 
 
1920} DENDROPHOMA LEAF BLIGHT OF STRAWBERRY 129 
 
 the summer and autumn. Half or two-thirds of a leaflet may die 
 as a result of the attack and often entire leaves are killed. This 
 results, of course, in a loss of vigor of the entire plant. 
 
 ISOLATION AND CULTURAL CHAEACTERS 
 
 Isolation. In order to determine the cause of leaf blight, the 
 fungus evident on the diseased parts of a leaf was isolated and grown 
 in pure culture. Some diseased leaves were placed in a moist cham- 
 ber for several days. From the pycdia abundant spores issued in 
 short, thick threads (cirrhi). Agar plates were made from these in 
 the usual manner and single spore cultures were obtained. Another 
 set of cultures was obtained by crushing the pycnidia on sterile slides 
 and pouring plates. In both cases it was comparatively easy to ob- 
 tain pure cultures. Oat agar was found to be an excellent medium 
 for isolation and was used in subsequent studies for growing the 
 fungus. The cultures were kept in the incubator at 24 C. 
 
 Cultural Characters. No extensive study of cultural characters 
 was made. On apple-bark agar the fungus formed a heavy, white 
 growth which was closely confined to the medium. The aerial my- 
 celium was scant. Scattered stromatic masses were developed in most 
 of the tubes. There were usually only three or four of these in each 
 tube. Later, several pycnidial chambers were formed in these struc- 
 tures with ostioles extending in various directions, thus forming a 
 studded structure from 2-4 mm. in diameter. The spores oozed in 
 quantities from the ostioles after the culture was two weeks old. 
 Single pycnidia were rarely observed on apple-bark agar ; they were 
 more common on plates than in the tubes. 
 
 Spores streaked on oat agar (Clinton's formula) resulted in a 
 mycelial growth similar to that described above but even more closely 
 confined to the agar. Abundant single pycnidia were formed over the 
 surface of the agar within a week and the spores oozed from these 
 in great abundance. The distinguishing character of the growth in 
 oat agar, aside from the abundant production of pycnidia, was the 
 production of a lemon-yellow pigment after five days. This was first 
 noticed at the bottom of the slant but it gradually spread upward. 
 
 MORPHOLOGY AND LIFE HISTORY 
 
 Mycelium. The hyphae remain light colored in culture for a 
 month or more. There are no pecularities in the branching or type 
 of growth by which the fungus can be distinguished. In the leaf 
 the mycelium penetrates all parts of the tissue. 
 
 Pycnidia. The pycnidia develop beneath the epidermis. As they 
 grow, the epidermis is pushed upward and finally ruptured in a star- 
 
130 BULLETIN No. 229 [July, 
 
 like manner. With a good lens the segments of the epidermis may 
 be seen pressed against the surfaces of the protruding pycnidia. The 
 pycnidia seem to be embedded more deeply in the tissues on the lower 
 surface than on the upper. When placed under moist conditions, 
 the pycnidia swell to several times their normal size and extend well 
 above the surface of the leaf. The neck of the pycnidium is conical, 
 thus making the entire pycnidium pear-shaped rather than flask- 
 shaped (Fig. 2). The unusual length of the neck of the pycnidium 
 
 FIG. 2. CROSS-SECTION OP A DISEASED LEAF, SHOWING THE LOCATION 
 OP THE PYCNIDIUM AND THE EXTRUDING NECK 
 (Drawn by E. F. Guba) 
 
 is a striking characteristic of this fungus both on leaves and in cul- 
 ture, but this character is very variable. 
 
 The wall of the pycnidium is light brown under high magnifica- 
 tion but the pycnidia are black to the naked eye. The walls are thin 
 and delicate so that it is difficult to separate the pycnidia from the 
 matrix of the leaf without rupturing them. The pycnidia are from 
 200 to 300 microns in diameter. 
 
 The spores issue from the pycnidia in long, thick, gelatinous cirrhi 
 when the surrounding atmosphere is moderately humid. In about 
 half the cases observed, the cirrhi did not arise from the ostiole but 
 were pushed out from the side of the pycnidium. A few cases were 
 noticed where two cirrhi originated from a single pycnidium, one on 
 either side of the neck, or one arising from the ostiole and the other 
 from the side of the pycnidium near the base of the neck. When 
 first removed from a moist chamber, the cirrhi are thick and pearl 
 colored; as the leaf dries, they shrink markedly and are honey col- 
 
19&0] DENDROPHOMA LEAF BLIGHT OF STRAWBERRY 131 
 
 ored. When moist they are easily removed on the point of a needle, 
 but when dry they are hard and tightly cemented to the pycnidium. 
 
 The spores exude from the pycnidia in the open when the leaf 
 becomes moist. During a dry period in September, spores were -ob- 
 served exuding in the morning after a moderate dew, thus showing 
 that rains are not necessary to supply ^ sufficient moisture for spore 
 exudation. 
 
 Spores The spores are hyaline, continuous, oblong-bacilloid, or 
 narrowly ellipsoidal (Fig. 3). They are unusually narrow for spores 
 of this genus. Two or three large 
 granules usually are evident at 
 
 either end, thus giving, a character- ^ u fl 
 istic appearance (biguttulate) to the <K /?# *L 
 
 spores under the high power of the y^f j 
 
 microscope. Exuding spores on the "^ 
 
 leaf measure 5-7 X 1.5-2 microns, 
 while in culture they are slightly 
 
 larger Freshlv oxndprl snnrp^ arP Fi ' 3 '~ Dendroptomaobscurans. 
 my exuaea spores are (a) Branched C0 nidiophore; (b) 
 
 remarkably constant in size, rarely Pycnospore 
 varying a micron in length. 
 
 The spores were germinated with difficulty in hanging drops of 
 tap water. In agar plates only about 1 percent germinated. No 
 explanation for this erratic behavior can be given. The pycnidia will 
 exude spores at any time during the winter or spring when condi- 
 tions are favorable. Leaves were brought into the laboratory every 
 month from September until May, and when placed in a moist cham- 
 ber sodn began to exude spores in abundance. Cultures could al- 
 ways be made from the spores. This explains a possible source of 
 infection in the spring. 
 
 ConidiopJiores. These are peculiar in that they are quite long 
 and distinctly branched. (Fig. 3.) 
 
 No perfect stage of the fungus was found altho repeated search 
 was made on old leaves during the spring. This stage would not 
 be necessary in the life history of the fungus since the pycnidia live 
 thruout the winter and produce viable spores in the spring. 
 
 Twelve strawberry plants were potted and all but the very young 
 leaves were removed. These plants were allowed to grow undisturbed 
 for three weeks and during this period no signs of the disease ap- 
 peared on the leaves. Some older leaves were then removed and the 
 young leaves left to develop. In several of the pots runners had 
 been sent out and had developed new plants by this time. Four of 
 the plants were sprayed with a suspension of spores from a pure 
 culture, four were sprayed with a suspension of spores obtained from 
 
132 BULLETIN No. 229 [July, 
 
 diseased leaves, while the remaining four were sprayed with sterile 
 tap water. The pots were covered with bell jars. After three days 
 the bell jars were removed and the plants kept well watered. After 
 ten days diseased spots appeared on several leaflets in all but one 
 of the pots where the spore suspensions had been used, while none 
 of the control plants showed any signs of the disease. 
 
 The lesions produced were typical except that the deep purple 
 color was absent, probably owing to the lack of light in the laboratory 
 and the succulent condition of the plants. It was expected that 
 numerous lesions would appear on each leaflet inoculated, but as a 
 rule there were only two or three and on about 50 percent of the 
 leaflets no infection was evident. In some cases the leaflets blighted 
 with no indication of a definite lesion and it was thought that these 
 had been more or less heavily infected but that they had wilted so 
 rapidly and completely that no fruiting bodies had been produced 
 on them. No insects were observed on any of the plants from the 
 time they were brought into the laboratory. Three of the infected 
 plants died about ten days after the disease first appeared. These 
 were discarded since the cause of their death was not thought to be 
 due entirely to the fungus under consideration. 
 
 Two plants which had been infected with spores from pure cul- 
 ture were used to isolate the fungus. From the edge of a lesion on 
 one of these plants, a pure culture was obtained from the mycelial 
 growth in the tissue. Pycnidia were developed on the lesions of two 
 leaflets of the second plant and a pure culture was obtained from 
 the exuded spores. 
 
 HISTORY OF THE DISEASE 
 
 In 1893, Halsted 1 reported ' ' a new strawberry blight ' ' as follows : 
 "Mr. F. L. Stevens, in 1892, while a special student in my laboratory 
 and upon a visit to his home in Syracuse, New York, obtained speci- 
 mens of a blight upon strawberry leaves which has been under in- 
 vestigation since that date, and upon which the following report is 
 made." He then describes the symptoms, which correspond closely 
 to those given above, and states that the disease was found in several 
 points in New Jersey as well as in the neighborhood of Syracuse, New 
 York. He believes that the fungus causing the trouble belongs to 
 the genus Aposphaeria. He calls attention to the differences between 
 this -fungus and Phyllosticta fragaricola Desm. and Rob., which he 
 states is a European species. The fungus is described in some de- 
 tail and attention called to the prominent pycnidium. A recognizable 
 figure of the disease is included. From the description of the symp- 
 toms and the figure presented, there is no question but that this is 
 
 'Halsted, B. D. Diseases of the Strawberry. New Jersey Agr. Exp. Sta. 
 Ept. 14, 327-332. 1893. 
 
DENDROPHOMA LEAF BLIGHT OF STRAWBERRY 133 
 
 the disease under consideration. He calls attention to the biguttulate 
 spores, the prominent neck of the pycnidium, and the typical V- 
 shaped diseased area. He regarded the pycnidium as superficial and 
 hence placed the fungus in the genus Aposphaeria a natural mis- 
 take when one does not have sections of the pycnidia to examine. 
 
 The fact that the fungus resembles a Phyllosticta naturally raises 
 the question as to whether or not it is the same as Phyllosticta fraga- 
 ricola Desm. and Rob. The spore sizes correspond closely but in 
 other respects there is a decided difference. Two exsiccati specimens 
 of Phyllosticta fragaricola, Koumeguere 's Fungi Selecti No. 1327 and 
 Rabenhorst's Fungi Europaei No. 1758, in the herbarium of the De- 
 partment of Botany, University of Illinois, were examined. In both 
 cases it was at once evident that the disease caused by this fungus 
 is entirely different from the blight under consideration. The spots 
 were much smaller, rarely exceeding 3 mm., with a striking white 
 center. The disease caused by Phyllosticta fragaricola more nearly 
 resembles our strawberry leaf spot (Mycosphaerella Fragariae (Schw.) 
 Lind.) but the lesions are smaller and the centers whiter. Phyllosticta 
 fragaricola is reported from London, Ontario, 1 and is common in 
 Europe. 
 
 In 1894, Ellis and Everhart described a new fungus on cultivated 
 strawberry which they called Phoma obscurans. 2 The description 
 given by them is as follows: 
 
 "Spots 5-8 mm. in diameter with ferruginous center and broad purple 
 border, paler below, perithecia few, scattered, convex prominent. Sporules ob- 
 long elliptical, hyaline, 2 nucleate, 4.5 - 5.5 X 1.5-2 microns. Basidia simple, 
 lanceolate, fusoid, 8-12 X 1.5 microns. 
 
 "Phyllosticta fragaricola Desm. has similar sporules but the spots are much 
 smaller with a white center. The basidia also indicate Phoma and not Phyllosticta. 
 
 "On leaves of Fragaria (cult.) Nuttallburg, West Virginia and Newfield, 
 New Jersey." 
 
 The above description was repeated by Millspaugh and Nuttall in 
 ' ' Flora of West Virginia ' ' in 1896. 3 They give the type habitat ' ' On 
 leaves of Fragaria cult. July 8, 1894." 
 
 Two exsiccati specimens of Phoma obscurans E. & E., in the 
 herbarium of the Department of Botany, University of Illinois, in 
 Ellis and Everhart 's North American Fungi, were examined. No. 
 3258 has the following label: "Phoma obscurans E. & E., Proc. Acad. 
 Nat. Sci. Phil., 1894, p. 357. On leaves of cultivated strawberry, 
 Nuttallburg, West Virginia, Nov., 1894, L. W. Nuttall." In this 
 packet there are two leaflets with rather large spots in every way 
 similar to those of the disease under consideration. No. 3444 has 
 
 a Notae mycologicae. Ann. Mycol., 11, 546-568. 1913. 
 2 Proc. Acad. Nat. Sci., Philadelphia, 1894, p. 357. 1895. 
 "Millspaugh, G. F., and Nuttall, L. W. Flora of West Virginia. Field 
 Columbian Museum Publications, Botanical Series, 1 (1896), 107. 
 
134 BULLETIN No. 229 [July, 
 
 the following label: "Phoma obscurans E. & E., Millspaugh and 
 Nuttall, Flora of West Virginia, 1896, p. 107. On leaves of culti- 
 vated strawberry, Nuttallburg, West Virginia, Sept. 1895, L. W. 
 Nuttall." There are three leaflets in this collection, each showing 
 one dead area of the typical triangular form on which abundant 
 pycnidia are present. 
 
 The description of Ellis and Everhart is brief and the size of 
 the spots here indicated is much smaller than the average found in 
 the field. The exsiccati specimens show the spots much larger in 
 most cases than indicated by the description. 
 
 A fragment of a leaflet from specimen No. 3444 was secured and 
 from it a microscopic mount was made and spore measurements se- 
 cured. The spore measurements and general character of the spores 
 and pycnidia agreed closely with material from collections of the 
 writer. The spore lengths given by Ellis and Everhart are somewhat 
 less than those made by the writer from his material. 
 
 There is no question but that the disease described by Ellis and 
 Everhart is the same as the leaf blight under consideration. It is 
 evident that three collections were made, two by Nuttall in West 
 Virginia (July 8, 1894, and September, 1895) and one in Newfield, 
 New Jersey, at an unrecorded date, but during 6r before the year 
 1894. 
 
 TAXONOMY OF THE FUNGUS 
 
 It has been customary to restrict the genus Phoma to those species 
 of the Sphaerioidaceae-Hyalosporae occurring on stems while leaf 
 parasites are placed in the genus Phyllosticta. Ellis and Everhart 
 referred the species under consideration to Phoma rather than to 
 Phyllosticta on the basis of conidiophore characters. Just what con- 
 stituted the basis of this distinction is not clear from their description. 
 
 Halsted called the fungus Aposphaeria on account of the sup- 
 posedly superficial pycnidia. It is evident from Fig. 2 that the 
 pycnidia are by no means superficial. Aposphaeria has short, un- 
 branched conidiophores while in this species the conidiophores are 
 distinctly branched. 
 
 Saccardo 1 erected the genus Dendrophoma to include all Phoma- 
 like species having branched conidiophores. This genus is ordinarily 
 described as having a papillate ostiole while the species under con- 
 sideration has a rather long-necked pycnidium, which might be called 
 rostrate. Spaeronema has as one of its distinguishing characters a 
 rostrate pycnidium, but the neck of this genus is very long and the 
 conidiophores are unbranched. Therefore, it would appear that the 
 species under consideration has characters of both Dendrophoma and 
 Sphaeronema. On account of the fact that the neck is comparatively 
 
 2, 4. 1880. 
 
DENDROPHOMA LEAF BLIGHT OF STRAWBERRY 135 
 
 short and the conidiophores are branched, the writer is of the opinion 
 that this species should be placed in the genus Dendrophoma and 
 proposes the new combination Dendrophoma obscurans. 1 
 
 OTHER LEAF-INHABITING FUNGI OF THE STRAWBERRY 
 
 The common leaf spot of strawberry due to Mycosphaerella Fra- 
 gariae (Schw.) Lind. is the only other widely distributed leaf dis- 
 ease in Illinois. Ascochyta Fragariae Sacc. is reported as common 
 in New York. This fungus produces a subcircular purple spot which 
 becomes white with a dark purple margin. Ascochyta Fragariae has 
 not been found in Illinois. 
 
 In May, 1883, Earle collected a fungus on strawberry leaves at 
 Anna, Illinois, which Ellis and Everhart described as Septoria 
 aciculosa. 2 No further mention of this fungus could be found by 
 the writer. In April, 1920, Mr. E. F. Guba, an assistant in the De- 
 partment of Horticulture, sent some dead leaves of cultivated straw- 
 berry plants to the writer from near Anna for identification of the 
 fungus occurring on their surfaces. This proved to be the same 
 Septoria aciculosa E. & E., collected thirty-seven years previously 
 in this same locality. It has since been found to be widely distrib- 
 uted in this state. This fungus appears in dead or dying leaves of 
 the previous season and there is no reason to believe that it is 
 parasitic in nature altho most species of Septoria are classed as para- 
 sites. The distinguishing character of this fungus on the leaves is 
 the presence of relatively large black spots, .5-1 mm. in diameter, 
 which resemble small sclerotia. Under a lens these appear to be 
 composed of grouped pycnidia as described by Ellis and Everhart. 
 
 CONTROL MEASURES 
 
 No experiments on the control of leaf blight were attempted in 
 connection with this study. While the disease causes serious loss of 
 functioning leaf tissues, it is not considered of sufficient economic 
 importance to warrant spraying or other expensive control measures. 
 Since infection evidently takes place thru the greater part of the 
 growing season, it would be necessary to spray over a relatively long 
 period. 
 
 ^Dendrophoma obscurans nov. comb. Spots large, .5-3 cm. or more ; circular, 
 oval, or sometimes fan-shaped; brown with broad purple zone. Pycnicia scat- 
 tered, amphigenous, flask-shaped, 150 - 300 microns, erumpent. Pycnosporcs 
 hyaline, continuous, bacilloid or narrowly ellipsoidal, biguttulate, 5 - 7 X 1.5 - 2 
 microns. Conidiophores long, branched. On living leaves of cultivated straw- 
 berry. 
 
 2 Torr. Bui., 11, 73. 1884. 
 
136 BULLETIN No. 229 [July, 1920} 
 
 The practice of mowing the leaves of the old vines and cultivating 
 after harvest is believed to reduce the amount of trouble from this 
 blight. On a patch where mowing was done the new leaves and 
 young plants appeared almost free of the disease during the latter 
 part of the growing season. 
 
 The practice of spraying strawberries for the common leaf spot 
 and insect troubles has not become general in Illinois and unless more 
 extensive damage should be done by this leaf blight in the future, it 
 would not be considered advisable to make special applications of 
 spray mixture for its control. 
 


UNIVERSITY OF ILLINOIS-URBANA