Assessment of potential candidate genes for partial resistance to Sclerotinia stem rot caused by <i>Sclerotinia sclerotiorum</i> using real‐time quantitative PCR

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum (Lib) de Bary (S. sclerotiorum), is one of the most important diseases that causes significant soybean [Glycine max (L.) Merr.] seed yield and quality losses in Canada and globally. Initiation of plant defense mechanisms is crucial for establishing partial resistance to the pathogenic fungus. To understand plant response to S. sclerotiorum, we conducted a temporal (1, 3, and 5 days post-inoculation [DPI]) assessment of gene expression changes in the stem of soybean genotypes with contrasting phenotypic response. We focused on four genes that have been previously reported as associated with SSR partial resistance and are known to be involved in defense-related functions such as cell wall modification, signaling, response to wounding, and response to fungus. The results showed a higher and earlier expression of the genes in partially resistant cultivars compared to the susceptible. Expression of some genes increased up to 11- (Glyma.02G059700) to 16-fold (Glyma.09G232100) by 3 DPI in the partially resistant cultivar, OAC Drayton, while the genes were generally downregulated in the susceptible cultivar, OAC Shire, at the same DPI. This study improves our understanding of expression patterns of genes involved in plant defense against fungal pathogens in soybean. More importantly, the knowledge of genes that are essential in defense against S. sclerotiorum can be used to fine-map the quantitative trait loci for SSR resistance and facilitate accelerated breeding of SSR-resistant cultivars through gene-based marker-assisted selection.