2019 ASHS Annual Conference

Spinach (Spinacia oleracea L., 2n=2x=12) is an economically important vegetable crop worldwide. The objectives of this spinach project are: (1) genetic mapping and SNP marker identification for downy mildew and white rust resistance; (2) QTL and association mapping, and SNP marker identification for Fusarium wilt resistance; (3) introgression of downy mildew and white rust resistance into spinach lines with diverse leaf quality characteristics to satisfy market demand; and (4) construction of high density SNP consensus genetic maps of the six chromosomes in spinach using whole genome resequencing. The project is a collaborative effort with the University of Arkansas, USDA-ARS at Salinas, Texas A&M AgriLife, and Washington State University. So far, 480 spinach genotypes have been evaluated for downy mildew, white rust, and Fusarium wilt resistance: downy mildew resistance was evaluated in Salinas, CA and Yuma, AZ during the winter of 2017-18 and winter of 2018-19; white rust resistance was/is being evaluated in a white rust nursery in Crystal City, TX and at Texas A&M AgriLife Research and Extension Center in Weslaco, TX during the winters of 2017-18 and 2018-19; Fusarium wilt resistance is being evaluated in the greenhouse at Washington State University Mount Vernon NWREC in Mount Vernon, WA. More than 20 spinach lines with high resistance to downy mildew, white rust, or Fusarium wilt have been identified. Nine F2 segregating populations have been evaluated for downy mildew. Thirteen, two and eight molecular markers have been developed for the loci RPF1, RPF2 and RPF3 for downy mildew resistance, respectively. A total of 440 spinach germplasm genotypes have been subjected to genome-wide association study (GWAS) and genomic selection (GS) for white rust resistance. Eight SNP markers were identified as a set to use for GS with a correlation coefficient (r) of 0.68 between the predicted breeding value and the observed white rust scale for 162 lines in a validation set, when another 250 spinach lines were used as the training set. GWAS is being completed for Fusarium wilt resistance, with SNP markers expected to be identified in 2019. The QTLs and SNP markers will provide breeders with robust tools to improve selection for resistance to these three economically important diseases of spinach through marker-assisted selection (MAS) and GS.