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POSTERS: Genetics of resistance

Disease development in cotton when co-inoculated with the soilborne fungi Fusarium oxysporum f. sp. vasinfectum race 4 and Rhizoctonia solani
Margaret Ellis - California State University Fresno. Mauricio Ulloa- USDA ARS, Robert B. Hutmacher- University of California, Davis, Shafter Research and Extension Center, Josue Diaz- California State University, Fresno

Fusarium oxysporum f. sp. vasinfectum (FOV) race 4 is a virulent wilt pathogen of cotton, that can also cause seedling damping-off when high levels of inoculum are present in the field. Rhizoctonia solani can also cause seedling disease in cotton. Previous speculations have suggested there is an increase in wilt symptoms caused by FOV race 4 when R. solani is simultaneously present in the field. Therefore, the goal of this study was to evaluate the possible interactions between FOV race 4 and R. solani in a co-inoculation assay. Planting material included one FOV race 4 susceptible line and four FOV race 4 resistant lines. Oat-infested inoculum, was prepared using isolates of FOV race 4 and R. solani. The infested oats were mixed with potting soil (1-part fungal inoculum to 3-parts potting soil) and cotton seeds were planted into one of the following treatments; FOV race 4 alone, R. solani alone, co-inoculation with both pathogens, and non-inoculated oats were used as a control. After six weeks, data for stand count, plant height, foliar and vascular symptoms were recorded. For all data collected the co-inoculation treatment was significantly different from the other fungal treatments (P<0.05), producing the greatest amount of disease symptoms. There was no significant difference between varieties. Our results suggest infection by R. solani may compromise the plants ability to compensate for FOV race 4 stresses thereby increasing FOV race 4 symptoms in the field.