Association Analysis and Identification of SNP Markers for Stemphylium Leaf Spot ( Stemphylium botryosum f. sp. spinacia) Resistance in Spinach ( Spinacia oleracea)

Abstract

Stemphylium leaf spot, caused by Stemphylium botryosum f. sp. spinacia, is an important fungal disease of spinach (Spinacia oleracea L.). The aim of this study was to conduct association analysis to identify single nucleotide polymorphism (SNP) markers associated with Stemphylium leaf spot resistance in spinach. A total of 273 spinach genotypes, including 265 accessions from the USDA spinach germplasm collection and eight commercial cultivars, were used in this study. Phenotyp-ing for Stemphylium leaf spot resistance was evaluated in greenhouse; genotyping was conducted using genotyping by sequencing (GBS) with 787 SNPs; and single marker regression, general li-near model, and mixed linear model were used for association analysis of Stemphylium leaf spot. Spinach genotypes showed a skewed distribution for Stemphylium leaf spot resistance, with a range from 0.2% to 23.5% disease severity, suggesting that Stemphylium leaf spot resistance in spinach is a complex, quantitative trait. Association analysis indicated that eight SNP markers, AYZV02052595_115, AYZV02052595_122, AYZV02057770_10404, AYZV02129827_205, AYZV0-2152692_182, AYZV02180153_337, AYZV02225889_197, and AYZV02258563_213 were strongly associated with Stemphylium leaf spot resistance, with a Log of the Odds (LOD) of 2.5 or above. The SNP markers may provide a tool to select for Stemphylium leaf spot resistance in spinach breeding programs through marker-assisted selection (MAS). A. Shi et al. 1601 Keywords Genotyping by Sequencing (GBS), Disease Resistance, Single Nucleotide Polymorphism (SNP), Spinacia oleracea, Stemphylium botryosum, Stemphylium Leaf Spot