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Xerox University Microfilms 300 North Zaab Road Ann Arbor, Michigan 4S106 76-24,671 RAO, Balakrishna, 1944- PYTHIUM ROOT ROT OF CORN: PYTHIUM GRAMINICOLA AND OTHER CAUSAL AGENTS INVOLVED; DETECTION OF P. GRAMINICOLA IN SOIL; AND EFFECTS OF TILLSGE^ ROTATION. FUNGICIDES, MOISTURE, AND TEMPERATURE. The Ohio State University, Ph.D., 1976 Agriculture, plant pathology Xerox University Microfilms,AnnArt»r,Michigan4etoe PYTHIUM ROOT ROT OF CORN: PYTHIUM GRAMINICOLA AND OTHER CAUSAL AGENTS INVOLVED; DETECTION OF P. GRAMINICOLA IN SOIL; AND EFFECTS OF TILLAGE* ROTATION, FUNGICIDES, MOISTURE, AND TEMPERATURE. DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Balakrishna Rao, B.Sc., M.Sc., M.S. * * * * * The Ohio State University * 1976 Reading Committee: Approved By Dr. A. F. Schraitthennor Dr, C. W. Eliott Co-Adviser, Department of Plant Pathology Dr. L. E, Williams 0 ^ Co -Advi ser, Dcparfyent of Plant Pathology ACKNOWLEDGEMENTS Tho author thanks his advisors Dr. A. P. Schmitthenner and Dr. C. W. Ellett for their guidance, encouragement, and constructive criticism during the course of this research and throught his graduate caroer. He wishes to express his appreciation to Dr. R. W. Caldwell for his suggestions, assistance and constructive criticism, and to Dr. L. E. Williams for reviewing the disscrtaion and offering helpful criticism. He is indebted to Dr. I. W. Deep and Dr. L. E. Williams for providing financial assistance and facilities. Thanks aro also extended to Dr. D. M. Van Doren for providing field plot facilities, to Dr. C. R. Weaver for statistical assistance, to Dr. G. Louie for providing seeds, and to Mr. G. Borkey for assistance with photography. Appreciation Is extended to staff members, graduate students, and technicians of the Department of Plant Pathology at The Ohio State University and The Ohio Agricultural Research, and Development Center. The author would like to thank one and all tho members of his and Borchers family for their encouragement and assistance throughout this investigation. ii VITA July 23, 1944 ... Born - Mysore, India. 1964 ........... B.Sc., University of Mysoro,'India. 1964-1966 ....... M.Sc., University of Bombay, India. Teaching. Merit scholarship recipient. 1966-1967 ....... Teaching, University of Bombay, India. 1967-1968 ....... Post M.Sc Diploma, Univorsity of Madras, India. UGC (University Grant Commission) scholarship recipient. 1969-1971 ... M.S., (Mycology), Univorsity of North Carolina. Teaching and Research Assistant. 1971-1973 ....... Worked on Biological control of Mosquitoes of medical importance with Dr. J. N. Couch, Univ­ orsity of North Carolina (NIH funded proj ect). 1973-1976 ....... Graduate Research Associate, Department of Plant Pathology, The Ohio State University and The Ohio Agricultural Research and Development Center, Wooster, Ohio. PUBLICATIONS 1. Rao,B., and W. J. Koch. 1970.' Fungal survey in waste ponds and c .• creek, Jta II. T. Odum and A. F. Chestnut cd. Studies of marine estuarino ecosystems developing with treated sewage wastos. Annual Report. 1969-1970. Univ. of North Carolina, Chapol Hill, '311-317 p. 2. Couch, J. N., S. V. Romney, and B. Rao. 1974. A new fungus which attacks mosquitoes and related Diptera. Mycologia 6 6 :374-3 1 7 . FIELD OF STUDY Major field: Plant Pathology. iii / TABLE OF CONTENTS Page ACKNOWLEDGEMENTS.......................... il vita . ....... m . LIST OF TABLES vi l i s t o f f i g u r e s ....................... viii INTRODUCTION ............ .................. 1 PART I: PYTHIUM ROOT ROT OF CORN: PYTHIUM GRAMINICOLA AND OTHER CAUSAL AGENTS INVfjLVtUTAND THEIR VIRULENCE Introduction 5 Materials and Methods............ 14 Results........................ 19 Discussion ....... ....... ......... 32 PART II: PYTHIUM ROOT ROT OF CORN: METHODS FOR DETECTION OP PYTHIUM GRAMINICOLA IN SOIL Introduction '. ....... 37 Materials end Mothods............ 40 Results ........... ........ 43 Discussion . ; ........ ; ; 1 ; . 52 * iv Page PART III: PYTHIUM ROOT ROT OP CORN: EFFECTS OF TILLAGE, ROTATION, FUNGICIDES, MOISTURE AND TEMPERATURE Introduction . .............................. 56 Materials and Methods ....................... 60 Results.................. ............... Discussion ..... ......................... 9* SUMMARY.............. 98 LITERATURE CITED........................................ 103 V LIST OF TABLES Tabic Number Page 1. Percentage of corn root lesions from which fungi wore isolated from field plots at bi-weekly intervals during 1974 and 1 9 7 S ...................................... 23 2. Bi-weekly summer precipitation at tho North Central Branch, 1974, and the North Westorn Branch, 1975 OARDC. 25 3. Fungi recovered on SAPBNC media at monthly intervals from roots of com. growing in tho greenhouse in field infested s o i l .......... .......................... 27 4. Relative virulence of Pythium spp. on corn seedlings using the petri dish water culture seedling test. .... 29 5. Number of surviving seedlings of two varieties of crested wheatgrass two weeks after planting in soil from tillage plots ..................................... 45 6. Mean number of total lesions and small lesions on corn seedlings roots suspended in water ovor throe different volumes of soil (CRT bioassay) collected at five sampling d a t e s ................ .................. 48 7. Mean lesion score and number of large lesions on corn seedling roots suspended in water over three different volumes of soil (CRT bioassay) collected at fivo sampling d a t e s ..................................... 49 8. Mean lesion number, lesion score, small lesions and large lesions on corn seedling roots suspended in water over three different volumes of soil (CRT bioassay) collected from two tillage systems on Toledo silty dlay s o i l ............ 51 9. Interaction of time with tillage and time with rotation for porcent root rot damage in1975 in Hoytville soil . 72 10. Percentage root damage in the best and worst tillage- rotation, fungicide treatments (TRF) in field plots in corn at different sampling tim e s .................... 74 vi Tabic Number Page 11. Numbers of small (type 1 and 2) lesions, large (typo 3, 4 and 5) lesions and percentage damage of corn seedling roots used for assaying Pythium levels in field soil at seven times during the growing season . 77 12. The effect of crop rotation on percent Toot damage in c o m havestcd at three different times in a greenhouse t e s t ........ gj 13. The effect of fungicides on percent root damage in c o m harvested at three different times in a greenhouse test . 82 14. The effect of moisture on percent root damage in c o m harvested at three different times in a greenhouse test . 83 15. Effect of moisture on number of small and large lesions on corn roots at three sampling times . .............. 85 16. Interaction of moisture, fungicides and time of isolation on recovery of Pythium gramirticOla and Fusarium spp. from disoased roots in the greenhouse . 87 17. Interaction of temperature and moisture on number of infected corn roots in growth chamber t e s t s............ 90 vii LIST OF FIGURES Figure Number Page 1. Corn root system with root rot symptoms ..... .20 2. Root rot rating* lesion types (small* large* streaked* girdled and necrotic) ........................... 21 3. Percentage of corn root lesions from which fungi were recovered in 1975 . ...................... 26 4. Crested whcatgrass seedling bioassay (CWG) method to detect levels of Pythium spp. in infested soil (tilled and nontillcd soil) ............................