Screening for Sclerotinia sclerotiorum resistance using detached leaf assays and simple sequence repeat markers in soybean cultivars

Abstract

Sclerotinia sclerotiorum (Lib.) de Barry, causal agent of Sclerotinia stem rot of soybeans, is one of the pathogens that could have a potentially devastating impact on the growth of the soybean industry in South Africa. Several quantitative trait loci (QTLs) that play a role in soybean resistance to Sclerotinia stem rot have been identified and mapped on the soybean integrated genetic linkage map. No cultivars planted in South Africa have been screened for the presence of these QTLs and their underlying markers, and limited current information on the resistance of these cultivars is available. A detached leaf assay was used to assess resistance of 29 soybean cultivars that are commercially grown in South Africa at temperatures of 20 °C and 25 °C as well as under low and high relative humidity. These cultivars were further screened for resistance to Sclerotinia stem rot using simple sequence repeat (SSR) markers, that are linked to resistance traits associated with Sclerotinia stem rot in soybean. Detached leaf assays revealed a significant difference (P < 0.001) in disease response across tested cultivars, while SSR markers revealed 10 cultivars that potentially have genetic-based resistance against Sclerotinia stem rot. Cultivars that showed a level of resistance to infection during the detached leaf assay were also more closely related to the Sclerotinia stem rot resistant cultivar Maple Arrow than to highly susceptible cultivar Williams 82; indicating the possible genetic resistance of these cultivars to Sclerotinia stem rot.