Genome-Wide Association Studies for Spot Blotch (Cochliobolus sativus) Resistance in Bread Wheat Using Genotyping-by-Sequencing

Spot blotch is a severe biotic menace of wheat caused by Cochliobolus sativus (syn. Bipolaris sorokiniana). Spot blotch is liable to major yield losses in warm humid regions. A genome-wide association study using genotyping-by-sequencing (GBS) markers was conducted to identify genomic regions associated with spot blotch resistance in a diversity panel of 159 spring wheat genotypes. In total, 87,096 GBS markers covering the whole genome, with an average polymorphism information content value of 0.276, were applied. Linkage disequilibrium (LD) analysis indicated that the LD decay extent was approximately 100 Mbp. The panel was evaluated for disease severity (DS) and area under disease progress curve (AUDPC) for 2 years. In total, 24 marker-trait associations (MTA) were identified for DS and AUDPC of spot blotch, with 11 on chromosome 5B, 3 on 3A, 2 on 6B, and 1 each on 1A, 2A, 1D, 2D, 4B, 5A, 7A, and 7B. A marker on chromosome 7B significantly explained 14% of the phenotypic variation of spot blotch severity as well as 11% of AUDPC. Five markers-three on chromosome 5B, one on 3A, and one on 7B-were associated with both DS and AUDPC with R2 ranging from 8 to 12%. Significant MTA can be utilized to develop wheat germplasm with resistance to spot blotch.