Variation in pathogen aggression and cultivar performance against Sclerotinia sclerotiorum in soybean and dry bean from Brazil and the U.S.

Sclerotinia sclerotiorum (Lib.) de Bary is an important yield-reducing disease in the United States and Brazil with a diverse host range, including dry bean and soybean. Characterization of both the physiological resistance of commercial cultivars to S. sclerotiorum and the range of aggressiveness among S. sclerotiorum isolates collected from locations where these cultivars are to be deployed, provides important information for making management recommendations. To address this in the present study, we first sought to characterize the range of S. sclerotiorum aggressiveness on soybean and dry bean, using a selection of isolates from Brazil and the U.S. Our second objective was to evaluate the performance of dry bean and soybean cultivars that were developed in Brazil. Eighty-seven isolates of S. sclerotiorum were collected from soybean crops from the U.S. and Brazil and used in this project. U.S. soybean cultivar Dassel and Brazilian dry bean cultivar IAC Alvorada were evaluated using a detached leaf bioassay (DLB) with 65 and 28 isolates respectively. For the straw test, U.S. dry bean cultivar G122 and Brazilian dry bean cultivar IAC Alvorada were inoculated with 32 and 28 isolates respectively. Results showed a significant difference among isolates (P < 0.001). After evaluating 23 Brazilian dry bean cultivars, results of the DLB and straw test showed IAC Diplomata and IPR Tangará were more tolerant to S. sclerotiorum. Among the 11 Brazilian soybean cultivars, M5410 and M6410 were found to be less susceptible to S. sclerotiorum. Collectively, results of this study are important for improving our understanding of variation in pathogen aggressiveness from geographically isolated populations and in identifying cultivars that are likely to have partial resistance.