Genome-Wide Association Study of Spot Form of Net Blotch Resistance in the Upper Midwest Barley Breeding Programs

Abstract

Pyrenophora teres f. maculata, the causal agent of spot form of net blotch (SFNB), is an emerging pathogen of barley in USA and Australia. Compared to net form of net blotch (NFNB), less is known in the United States upper Midwest barley breeding programs about host resistance and quantitative trait loci (QTL) associated with SFNB in breeding lines. The main objective of this study was to identify QTL associated with SFNB resistance in the upper Midwest two-rowed and six-rowed barley breeding programs using a genome-wide association study (GWAS) approach. A total of 376 breeding lines of barley were evaluated for SFNB resistance at the seedling stage in the greenhouse in Fargo in 2009. The lines were genotyped with 3072 single nucleotide polymorphism (SNP) markers. Phenotypic evaluation showed a wide range of variability among populations from the four breeding programs and the two barley-row types. The two-rowed barley lines were more susceptible to SFNB than the six-rowed lines. Continuous distributions of SFNB severity indicate the quantitative nature of SFNB resistance. The Mixed Linear Model (MLM) analysis, which included both population structure and kinship matrices, was used to identify significant SNP-SFNB associations. Principle component analysis (PCA) was used to control false marker-trait association. The linkage disequilibrium (LD) estimates varied among chromosomes (10 to 20 cM). The MLM analysis identified ten potential QTL in barley: SFNB-2H-8-10, SFNB-2H-38.03, SFNB-3H-58.64, SFNB-3H-78.53, SFNB-3H-91.88, SFNB-3H-117.1, SFNB-5H-155.3, SFNB-6H-5.4, SFNB-6H-33.74, and SFNB-7H-34.82. Among them, four QTL (SFNB-2H-8-10, SFNB-2H-38.03 SFNB-3H-78.53, and SFNB-3H-117.1) have not previously been published. Identification of SFNB resistant lines and QTL associated with SFNB resistance in this study will be useful in the development of barley genotypes with better SFNB resistance