The usefulness of sclerotia morphology traits and mycelial growth rate to infer phenotypic variability in populations of Sclerotinia sclerotiorum associated with common beans in Minas Gerais State (MG) was assessed in two experiments. Isolates (131) were collected in the Northwestern, Alto Paranaíba, Zona da Mata and Southern regions of MG and the mycelial growth rate, the number, weight and dimensions (length, width and thickness) of sclerotia and mycelial pigmentation were assessed. There was a high variability among isolates, even among colonies of the same isolate. The variance of the first experiment for the mycelial growth rate, number, weight, length, width and thickness of sclerotia, were 0. 01, 190.15, 0.01, 0.62, 0.12 and 0.05, whereas in the second, the variances were 0.01, 28.48, 0.002, 0.18, 0.06 and 0.03, respectively. Most correlations between traits were of low magnitude except that between length and width (r = 0.84, 'P < 0.001). Regarding colony pigmentation, non-pigmented, pigmented and highly pigmented isolates were identified, but for most isolates this characteristic varied between experiments. No groups based on phenotypic traits were detected. The morphological traits evaluated in the present study are not suitable for characterization of populations of S. sclerotiorum. Key words: Phaseolus vulgaris, sclerotium, phenotypic variability, white mold.Several biological features make the ascomycete Sclerotinia sclerotiorum (Lib.) de Bary a highly threatening fungal pathogen to important crops in Brazil. Sclerotinia sclerotiorum is a homothallic fungus that does not produce conidia, but abundant sclerotia (Bolton et al., 2006). Sclerotia are asexual resting structures that allow pathogen survival when no host is available (Adams & Ayers, 1979). The pathogen has a host range that encompasses over 400 plant species (Boland & Hall 1994). Furthermore, pathogen propagules (sclerotia) can be easily spread over long-distance by contaminated seeds. Sclerotinia sclerotiorum causes white mold in crops such as cotton, soybean, potato, sunflower etc., and is the main soilborne disease affecting common bean (Phaseolus vulgaris L.) in Minas Gerais State (MG), Brazil.In Brazil common bean is produced in the springsummer, summer-fall, and fall-winter growing seasons (Vieira et al., 2010). Considering the three growing seasons, MG is the second largest producer, but ranks first during the fall-winter, with an average yield of 2600 kg ha -1 (CONAB, 2013). In the fall-winter growing season, moderate temperatures and high humidity provided by irrigation create conducive environmental conditions for white mold epidemics (Paula Júnior et al., 2006). Planting white mold resistant cultivar would be attractive alternative for disease management. Nevertheless, to date there are no resistant varieties available to growers. Sound breeding programs require proper understanding of the pathogen variability. The variability of populations of S. sclerotiorum has been investigated for different crops around the world an...

The genetic structure of the population of Sclerotinia sclerotiorum was analyzed using 238 individuals collected from different hosts. Individuals were characterized for microsatellite genotypes and mycelial compatibility groups (MCGs). A total of 22 MCGs and 64 multilocus lineages (MLLs) were identified. There was a close relationship between the MCGs and MLLs, but there was no association between MLLs and hosts or regions. At least 39 MCGs are present in Brazil and 68.5% of the isolates were assigned to either MCG 1 or 2. Eight new MCGs were found. Seven genetic groups were identified and associated with MCGs. Most genetic variation (70.0%) was due to differences among MCGs. High values of estimates of linkage disequilibrium among loci were more frequent in the total population (all MCGs). In contrast, there was evidence of random mating in subpopulations defined by MCGs 1 and 2. Additionally, there was evidence of outcrossing in the population of S. sclerotiorum in Brazil. The population was structured by MCGs, lineages originated from asexual reproduction or selfing prevail and are widely distributed in space, are persistent in time and affect many hosts, but there is evidence of some degree of outcrossing which may lead to a more genetically variable population in the future.

The genetic structure of a population of Sclerotinia sclerotiorum causing white mold on common bean in Brazil was studied using microsatellite (SSR) loci and mycelial compatibility groups (MCGs). A total of 300 isolates were analyzed and 154 SSR haplotypes and 32 MCGs were identified. Two MCGs were widely distributed and accounted for 70% of the isolates. Six SSR haplotypes were associated with more than one closely related MCG. There was no evidence of random association of alleles among loci when the population comprised by all MCGs was analyzed, suggesting that outcrossing is absent or rare. Nevertheless, there was evidence of random mating within the major MCGs. Seven genetic groups were identified, one of them comprising only highly pigmented isolates. Isolates of distinct MCGs did not differ in virulence. There was strong genetic differentiation among MCGs: more than 95% of the total genetic variation was attributed to differences among these groups. Therefore, MCGs contribute to the structure of the population of S. sclerotiorum in Brazil.