Reaction of sources of resistance to white mold to microsatellite haplotypes of Sclerotinia sclerotiorum

White mold caused by the fungus Sclerotinia sclerotiorum is the most yield-limiting disease of common bean in Brazil. To date, there has been no commercial cultivar resistant to this disease. In a greenhouse we evaluated white mold resistance sources (Cornell 605, A195 and G122) against eight isolates of S. sclerotiorum from five Brazilian states. A Brazilian cultivar (BRSMG Madreperola) and a susceptible check (Beryl) were used as control. Treatments were arranged in factorial combinations (5 x 8) in a completely random design with four replicates. Disease severity was assessed on a rating scale of 1-to-9 together with lesion length, which was used to determine an area under the disease progress curve (AUDPC). Polymorphisms detected in ten microsatellite loci were used to assess variability between the isolates. Each isolate was a distinct haplotype; they formed a genetic tree with two clusters. One cluster was formed by three isolates collected from the states of Minas Gerais and Sao Paulo (southeastern); the others, by isolates from Parana, Santa Catarina (southern), Goias (Mid-western), and again, Minas Gerais. Genotype x isolate interaction was significant. In general, Beryl was more susceptible than BRSMG Madreperola. Considering the AUDPC and/or the white mold reaction score, Cornell 605 exhibited more physiological resistance than BRSMG Madreperola to seven isolates, A195 to five isolates, and G122 to two isolates. Our results suggest that Cornell 605 is the best source of resistance to white mold for the southern region, whereas Cornell 605 and A195 are somewhat superior to G122 for the southeastern and mid-western regions.