Resistance in spring wheat to the various diseases caused by Cochliobolus sativus by Aftabuddin Ahmed A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Plant Pathology Montana State University © Copyright by Aftabuddin Ahmed (1989) Abstract: Sixteen spring wheat cultivate were tested for their resistance to the various diseases caused by Cochliobolus sativus (Ito and Kurib.) Drechsl. ex Dastur. Five Montana isolates and four Bangladesh isolates of the fungus were used in whole plant inoculations in the Plant Growth Center and in laboratory tests using detached leaves. Sources of resistance were detected and identified for different phases of the disease. Ten cultivars were resistant to root rot, eight cultivars were resistant to foliar spot blotch, and six cultivars were resistant to head blight or black point. A number of cultivars showed differential reaction to various phases of the disease, e.g., were resistant to root rot but were susceptible to foliar spot blotch. Six cultivars, namely Marberg, GP248, GP253, GP254 and GP255, were resistant to all phases of the disease. The isolates tested differed significantly in pathogenicity, but considerable shifting in ranking occurred between experiments. Isolates obtained from roots were able to attack foliage/heads and vice versa. The isolates from Bangladesh did not have a higher temperature requirement than the USA isolates. Some cultivars were resistant to all isolates from both Bangladesh and the USA. The maximum disease development for root rot, foliar and head blight/black point phases occurred at 30°C with a 72 hour exposure to moist conditions. The disease reactions on detached leaves were not consistent with those on intact leaves. RESISTANCE IN SPRING WHEAT TO THE VARIOUS DISEASES CAUSED BY COCHLIOBOLUS, SATIVUS by Aftabuddin Ahmed A thesis submitted in partial fulfillment of the requirements for the degree Doctor of Philosophy in Plant Pathology MONTANA STATE UNIVERSITY Bozeman, Montana December 1989 -DSrJS ii APPROVAL of a thesis submitted by Aftabuddin Ahmed This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. Date CS Chairperson, Graduate Committee Approved for the Major Department Date (S Head, Major Department Approved for the College of Graduate Studies Date Graduate Efean iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a doctoral degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. I further agree that copying of this thesis is allowable only for scholarly purposes, consistent with "fair use" as prescribed in the U iS. Copyright Law. Requests for extensive copying or reproduction of this thesis should be referred to University Microfilms International, 300 North Zeeb Road, Ann Arbor, Michigan 48106, to whom I have granted "the exclusive, right to reproduce and distribute copies of the dissertation in and from microfilm and the right to reproduce and distribute by abstract in any format." Signature Date iv ACKNOWLEDGEMENTS I wish to express my sincere appreciation and thanks to Dr. D. E. Mathre1 my co-major professor, for his advice, encouragement, guidance, and patience, for providing me all the facilities needed for my research, and for help during the preparation of this thesis. I also want to express my appreciation to Dr. A. L. Scharen, my co-major professor, for his continued interest and encouragement in the course of the study and preparation of this thesis. It is my pleasure to also recognize the assistance and invaluable advice of Dr. T. W. Carroll, Dr. J . M. Martin, Dr. G. A. Taylor and.Dr. W. W. Locke while serving on my graduate committee. Thanks are expressed to Dr. R. E. Lund for his help in statistical analysis of data and to R. H. Johnston and W. E. Grey for their assis­ tance in overcoming numerous obstacles during this study. I am thankful to the Bangladesh Agricultural Research Institute for providing me financial support through a grant under the International Maize and Wheat Improvement Center's program of assistance sponsored by the Canadian International Development Agency. A very special thanks to my wife Anwara, sons Tareque and Mamun and daughter Afroza for their patience and love. Finally, appreciation is extended to Wanda Myers for neatly typing this thesis. V TABLE OF CONTENTS Page LIST. OF TABLES . ............................................. vii LIST OF FIGURES ................................................ xiv A B S T R A C T ......................................................... xv INTRODUCTION ..................... .......... .......... .......... 1 REVIEW OF LITERATURE ............................. 4 The Disease . ................... 4 S y m p t o m s ............................... g Economic Importance ........................................ g The Pathogen ................................. 9 Physiological Specialization ............................... XO Epidemiology ................................. X2 Resistance in Spring Wheat .................................. 16 MATERIALS AND METHODS ............................................ 18 Sources of G e r m p l a s m .................; ..................... 18 Isolation and Maintenance of Cochliobolus sativus . 18 Preparation of Inoculum ............................... 19 Method #1 19 Method #2 19 Root/Subcrown Internode Inoculation ................... 20 Foliar Inoculation ...................................... 22 Screening for Resistance to Black Point .............. 24 Evaluation of Resistance Using Detached Leaves ............. 25 Generation of I n o c u l u m .................................. 25 Generation of Leaf Material . ;.................; 25 Effect of Temperature and Post-Inoculation Moist Period on the Pathogenicity of CL, sativus 26 vi TABLE OF CONTENTS --Continued Page RESULTS ......................................................... 28 Evaluation of Germplasm ............................... 28 Subcrown Internode.Inoculation ........................ 28 Foliar Inoculation ......................... 30 Evaluation of Resistance to Black Point .................... 34 Evaluation of Resistance Using Detached Leaves .............. 36 Effect of Post-Inoculation Temperature and Moisture Period on the Pathogenicity of CL. sativus ................. 54 D I S C U S S I O N ....................................................... 68 SUMMARY ......................................................... 76 R E F E R E N C E S ....................................................... 77 APPENDIX 88 vii LIST OF TABLES Table Page 1 Reaction of 16 spring wheat cultivars to subcrown internode inoculation with nine isolates of Cochliobolus sativus under greenhouse conditions .... 29 2 Relative pathogenicity of nine isolates of Cochliobolus sativus on subcrown internodes of 16 spring wheat cultivars under greenhouse conditions . 31 3 Reaction of 16 spring wheat cultivars to foliar inoculation with three isolates of Cochliobolus sativus under greenhouse conditions ................... 32 4 Relative pathogenicity of three isolates of Cochliobolus sativus on foliar infection of 16 spring wheat cultivars under greenhouse conditions .......... 33 5 Black point incidence in 16 spring wheat cultivars inoculated with three isolates of Cochliobolus sativus under greenhouse conditions ................... 35 6 Relative pathogenicity of three isolates of Cochliobolus sativus on black point incidence of 16 spring wheat cultivars under greenhouse conditions . 35 7 Effect of temperature on disease reaction of 16 spring wheat cultivars on detached seedling and mature leaves inoculated with nine isolates of Cochliobolus sativus .................................... 36 8 Lesion length on detached seedling leaves of. 16 spring wheat cultivars inoculated with nine isolates of Cochliobolus sativus at three temperatures ........ 37 9 Necrotic area of detached seedling leaves of 16 spring wheat cultivars inoculated with nine isolates of Cochliobolus sativus at three temperatures ............. 38 10 Percent necrosis of detached seedling leaves of 16 spring wheat cultivars inoculated with nine isolates of Cochliobolus sativus at three temperatures ........ 40 viii LIST OF TABLES- -Continued Table Page 11 Ranking of 16 spring wheat cultivars from scores obtained for lesion length, necrotic area, and percent leaf necrosis on detached seedling leaves at different temperatures ........................... 41 12 Lesion length of detached mature leaves of 16 spring wheat cultivars inoculated with nine isolates of Cochliobolus sativus at three temperatures .......... 42 13 Necrotic area of detached mature leaves of 16 spring wheat cultivars inoculated with nine isolates of Cochliobolus sativus at three temperatures .......... 43 14 Percent necrosis of detached mature leaves of 16 spring wheat cultivars inoculated with nine isolates of Cochliobolus sativus at three temperatures .... 44 15 Ranking of 16 spring wheat cultivars from scores obtained for lesion length, necrotic area, and percent leaf necrosis on detached mature leaves at different temperatures ............................... 46 16 Effect of isolates of Cochliobolus sativus on lesion length development on detached seedling leaves of 16 spring wheat cultivars at three