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TECHNICAL SESSION: Fungal and oomycete pathogens: New approaches to disease resistance

Classical breeding and gene-silencing: multi-pronged strategies to address incomplete resistance to Sclerotinia stem rot in soybean (Glycine max)
Megan Mccaghey - University of Wisconsin-Madison. Ally Lindstrom- University of Wisconsin-Madison, Mehdi Kabbage- University of Wisconsin-Madison, Dandan Shao- University of Wisconsin-Madison, Ashish Ranjan- University of Wisconsin-Madison, Damon Smith- University of Wisconsin-Madison, Jake Kurcezewski-

Soybean (Glycine max) resistance to Sclerotinia sclerotiorum is incomplete, and yield losses from Sclerotinia stem rot (SSR) can exceed 300 kg/ha for every 10% increase in severity. We aim to enhance resistance to SSR using classical breeding and modern RNAi methods. Newer soybean germplasm, identified through selections in the greenhouse and field nurseries, has served as an unprecedented source of high physiological resistance to SSR. Crosses integrating this germplasm with susceptible, high-yielding lines has been recently accomplished. Additionally, the pathogenic success of S. sclerotiorum requires the secretion of oxalic acid (OA). Virus-induced gene silencing (VIGS) was used to target OA biogenesis in S. sclerotiorum. A sequence corresponding to the fungal oxaloacetate acetylhydrolase (Ssoah1) was cloned into a BPMV vector and introduced into G. max. Plants containing BPMV vectors targeting Ssoah1 had significantly enhanced resistance to S. sclerotiorum (P=0.0035) and significantly lower expression of Ssoah1 (P=0.0003), compared to empty-vector control plants, 48 hours post inoculation. Our study also evaluated exogenous applications and uptake of dsRNA by S. sclerotiorum to limit OA production. These results provide evidence supporting host-induced gene silencing and exogenous applications of dsRNA targeting virulence factors as viable strategies to control SSR. Combining classical breeding with RNAi technology may offer superior resistance to SSR in G. max.