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Studies on Rhynchosporium Secalis (Oud.) Davis

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Studies on Rhynchosporium Secalis (Oud.) Davis STUDIES ON RHYNCHOSPORIUM SECALIS (OUD.) DAVIS CAUSING SCALD OF BARLEY Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University HOWARD ERNEST REED, B. S., M. S The Ohio State University 1953 Approved tyi ACKNOWLEDGEMENTS The writer wishes to express his sincere gratitude to his adviser, Dr. C. C. Allison, for guidance and many helpful suggestions given in the present study. A word of thanks is also extended to Dr. Patricia Allison for critical reading of the dissertation. Dr. G. A. VTiebe of the U. S. Department of Agriculture, Beltsville, Maryland, was also helpful by providing seed from the World Barley Collection. Appreciation is expressed to various members of the University of Tennessee Agriculture Experiment Station Staff for helpful suggestions during the course of the research. TABLE OF CONTENTS Page INTRODUCTION ................................................. 1 LITERATURE R E V I E W ............................................ 2 MATERIALS AND METHODS ........................................ 9 EXPERIMENTAL RESULTS............................................ 17 Physiologic Variation of Isolates from Barley.............. 17 Epidemiology.............................................. L6 DISCUSSION AND CONCLUSIONS ..................................... 56 SUMMARY ........................................................ 62 LITERATURE C I T E D ................................................ 65 AUTOBIOGRAPHY.................................................. 6? 11 STUDIES ON RHYNCHOSPORIUM SEGALIS (OUD.) DAVIS CAUSING SCALD OF BARLEY INTRODUCTION Scald caused by Rhynchosporium secalis is a consnon foliage disease of barley in most parts of the world. In the United States the disease, until recently, has caused severe damage only in certain barley growing regions. The disease has become increasingly widespread since 19Ui» causing severe damage in areas where it had formerly been unknown or only of minor importance. In the United States, the disease has received little attention, except for the study made by Caldwell (3). The present studies, initiated in Tennessee in 19U8, include the physiologic variation of the fungus isolated from barley leaves from various parts of the United States and Canada, and epiphytology of the disease in east Tennessee. It is hoped that these studies will result in a better understanding of the recent widespread occurrence and severity of the disease, as well as suggest possible means of control. 1 2 LITHtATURE REVIEW The fungus inciting scald of cereals and grasses was first discovered by Oudemans (10) in June of 1897 on rye in the Netherlands* He named it Marsonia secalls n. sp. Four months later, according to Frank (5), Heinsen had renamed the fungus Rhynchosporium graminlcola Heinsen. Davis (h)> in 1919, believing that Oudemans had incorrectly classified the fungus, recognized Heinsen's genus Rhynchosporium, and named the fungus Rhynchosporium secalis (Oud.) Davis according to the International Rules of Nomenclature. The fungus was first adequately described by Frank (5) in 1897* He observed it on barley and rye in Germany and, in herbarium specimens, found evidence that the disease occurred as early as 189U* Scald was first reported to have been prevalent in 1915 in the United States (6). The disease is now world wide in areas of barley production. Scald has been observed in the Upper Mississippi Valley for many years. Generally the disease in this area has been local and scattered in distribution with occasional reports of severe damage in limited areas. In certain sections of the Pacific Coast, especially in California, the disease has been a major limiting factor in barley production. Recent reports of epiphytoties of scald have been made by Poehlman (11) in Missouri (19hh and 191*5), Riddle and Suneson (13) in California (19U7), Rosen and Larch (17) in Arkansas (19U1*), Roane and Starling (15) in Virginia (1951)# and Reed (12) in Tennessee (1951)* Weston (21) in East Anglia (19Uh) reported an epiphytotic of scald, as did Rodriguez Vallejo (16) in Mexico (191*7 )• Conflicting reports have been made regarding the host specialization of R. secalis. Heinsen (7) in Germany (1901) found no specialization of the fungus on cereals. Using host borne conidia as inoculum, he claimed that barley and rye were equally susceptible, while wheat was only slightly susceptible and oat was immune. Bartels (1), in Germany (1928), inoculated plants of barley, rye, oats, wheat, Agropyron, Agros tis, Bromus, Cynosurus, Horde uni, Lolium, Holcus, and Rhleum with cultures of R. secalis isolated from barley, rye, Hordeum murinum, and Lolium perenne. Scald developed on all except wheat and oat. Brooks (2), in England (1928), made no inoculations but states, ”R. secalis occurs on a considerable number of wild grasses, and these undoubtedly may be a source of infection to crop plants.'* He found R. secalis on Bromus sterilis, B. mollis, and Dactylis glomerata, as well as upon barley and rye. In contrast to the above studies in which there was little or no host specialization, are those of Caldwell (3) in the United States. Using monoconidial cultures of R. secalis isolated from barley, Hordeum jubatum, Agropyron repens, Bromus inermls, Elymus canadensis, and rye, he found that each isolate was pathogenic only on the host from which it was isolated. He described a new species, Rhynchosporium orthosporium on Dactylis glomerata. Sarasola and Campi (18), in Argentina (19U7)> studied physiologic specialization of ten monoconidial cultures isolated from barley upon sixteen different barley varieties. They also made Inoculations of two different monoconidial cultures of R. secalis isolated from barley upon Agropyron smithil, Alopecurus pratensis, Avehenaterum elatior, Avena barbata, A. bysantine, A. nuda, A. sativa var. orientails, A. strigosa, Bromus Inenals, B. carinotus, B. unlololdes, Pactyll3 glomerata, Elymus canadensis, Festuca elatior var. arundinaceae, F. idahoensis, Hordeum bulbosum, Lolium multiflorum, L. perenne, 0ry3opsis hymenoides, Fhleum pratense, Secale cereale, and Stipa lemonnii. Of the above grasses and cereals inoculated in the greenhouse, Bromus unioloides, Agropyron smlthii, Elymus canadensis, and Festuca elatior var. arundinaceae were found to be susceptible. The authors concluded that R. secalis isolated from barley in Argentina differs, in its host specialization upon different genera of Gramineae, from the fungus occurring in the United States and Germany. The same investigators tested 21*0 barley lines by bringing about an epiphytotic of the disease in field test plots with one monoconidial culture isolated from barley. Sixteen of the most highly resistant barley lines found in the field test were then inoculated with each of ten different monoconidial cultures obtained from different parts of Argentina. Three barley lines, West China C. I. 7556, Wisconsin Winter X Glabron 2073 0. I* 8162, and Nigrum fl» Ii were found to differ in degree of susceptibility to different cultures, being either susceptible or resistant. These three barley varieties differentiated the . cultures into ii physiologic races as given in Table 1. Some work has been done on variation of isolates of R. secalis in culture. Heinsen (7) found that the fungus either sporulated abundantly or was highly mycelial on different media. Upon prune, beet, and oat decoctions the fungus formed abundant hyphae with few conidia, while upon rye, barley, wheat, grass, and fruit juice decoctions the fungus formed abundant conidia and very little nycelium. Caldwell (3) 5 Table 1. Classification of physiologic races of R. secalis isolated from barley in Argentina, according to Sarasola and Campi (18). Key to Races Race 1. Wisconsin Winter X Glabron 2073, resistant: 2. West China, resistant: 3. Nigrum resistant ............................ 1 3. Nigrum susceptible .......................... 2 2. West China susceptible .......................... 3 1. Wisconsin Winter X Glabron 2073, susceptible .......... U cultured rye and barley isolates upon barley- and rye-leaf decoction agarsj corn mean, and corn meal-1 per cent dextrose agars; lima bean agar; oatmeal agar; potato agar, potato-1 per cent dextrose agar, and potato-2 per cent dextrose agar; 1- and 2-per cent malt extract agars; and upon sterilized barley stems. Nine monoconidial cultures isolated * from barley were included in his study* The volume of mycelium and abundance of conidia on these media varied directly with the concentration of dextrose or soluble carbohydrate present. He found conidia most nearly resembling those occurring on the host on media with low sugar content such as corn meal, oat meal, and lima bean agars. The type of growth of any one race was similar upon malt agar and potato-dextrose agar containing 1*5 per cent fiacto-agar and 2 per cent of malt extract and dextrose respectively, although all races grew more rapidly upon potato dextrose agar. He distinguished two general types of growth. Rhynchoaporiua orthoaporluro from Dactylis glomerata and races of R. secalis from rye, Bromus inermis, and Elymua canadensis developed from the point of transfer in a uniform radial manner, while e races from barley and Agropyron repens formed heaped-up, irregular masses of mycelium and conidia. The races differed markedly in pigmentation in culture. Cultures of the barley race became black after two weeks; cultures of the race from Agropyron repens were likewise black but had a pink
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