Phenotypic and genotypic characterization of single isolate-derived monoascospore strains of Sclerotinia sclerotiorum from common bean

Abstract

White mold is a highly destructive disease caused by Sclerotinia sclerotiorum, a polyphagous fungus that infects several hosts including common bean grown that is widely cultivated in Brazil. The pathogenic populations are known to exhibit genetic variability but studies rarely used single ascospore-derived strains. In this study, 12 monoascospore strains originated from a same isolate (UFLA 54), but from different apothecia, were compared among them and with the mother strain with regards: days to first sclerotium formation, mycelial growth rate mycelial compatibility groups, microsatellite markers and mating type locus (MAT1-1 and MAT1-2). Their pathogenicity was assessed on three common bean lines. Cluster analysis of growth rates data separated UFLA 54 from all monoascospore strains, which shared same alleles in the microsatellite locus. Inversion of MAT1-1 region was found for both UFLA 54 and half of monoascospore strains. Aggressiveness of the monoascospore strains was not consistent across common bean lines. Our study reveals significant variability of S. sclerotiorum at the single isolate level. Keywords Phaseolus vulgaris. White mold. Aggressiveness. Morphological traits White mold is a fungal disease caused by Sclerotinia sclerotiorum (Lib.) de Bary, a necrotrophic and homothallic fungus capable of infecting several hosts and causing severe epidemics in important field crops including soybean, common bean and sunflower. White mold epidemics are reported worldwide, including Brazil, with yield losses estimated at 19% to 70% depending on the geographic region and year (

Resistance of common bean lines to Sclerotinia sclerotiorum isolates under different environmental conditions

“…Positive correlations between the severity assessments performed in the field and greenhouse have been observed in some studies (Soule et al, 2011;Leite et al, 2016;Chauhan et al, 2020). Breeders could take advantage of this correlation to obtain high levels of resistance to white mold (Schwartz & Singh, 2013), since the results obtained in the field derive from the combination of physiological resistance and escape mechanisms (Abreu et al, 2019).…”

“…Plants were kept in a greenhouse with 25±2°C and 75 % moisture. Mycelium discs were removed from the edges of the 4-day colonies, using 200 µL pipette tips, and put at the apex of the main stem of 28-day-old plants (Abreu et al, 2019). Seven days after inoculation, the reaction of all common bean plants to white mold was assessed on a diagrammatic 1-9 scale (Singh et al, 2014); where: 1 represents no sign of inoculated internode infection, immune or completely healthy; and 9 represents the disease infection >1 inch after the second inoculation node, leading to plant death.…”

“…This disease is caused by the necrotrophic fungus Sclerotinia sclerotiorum (Lib.) de Bary, which has a high genetic variability, even in clonal populations (Abreu et al, 2019;Attanayake et al, 2019;Abán et al, 2021). Sclerotia are the central component of epidemics as they are long-term survival structures, and as a resistant structure, they can survive for a long time in the soil.…”