P-024 - Discovering cqSCN-007, a Novel Type of Resistance to Soybean Cyst Nematode

Soybean cyst nematode (SCN) is by far the most damaging disease of soybean in the U.S. Although genetic resistance is the most effective strategy against SCN, most commercially grown soybeans rely on a single type of resistance that is losing efficacy as SCN populations slowly evolve.  Wild ancestors of domesticated plants offer naturally occurring new alleles. One example is cqSCN-007, derived from Glycine soja PI 468916, which confers quantitative but significant resistance to SCN.  cqSCN-007 has been introgressed into elite soybean genotypes and delimited to an 11-gene genetic interval. The genes within this genetic interval do not include obvious candidates based on their annotation with respect to well-established plant defense processes or based on polymorphisms between resistant and susceptible haplotypes. Initial efforts to identify the functional gene via RNAi or CRISPR knockouts in detached transgenic roots were impeded by weak expression of resistance in petri plate assays.  To identify the causal gene, we are now conducting reverse genetics using composite plants (transgenic roots on non-transgenic shoots) and investing in the generation of transgenic soybean lines. We are also identifying SCN populations that most strongly reveal the quantitative resistance phenotype.  Determining the causal gene(s) will facilitate breeding for this QTL, new allele discovery and genetic engineering for improved disease control of this major agricultural disease.