Identification and validation of a novel locus, Qpm-3BL, for adult plant resistance to powdery mildew in wheat using multilocus GWAS

Background: Powdery mildew (PM), one of the major diseases in wheat, severely damages yield and quality, and the most economical and effective way to address this issue is to breed disease-resistant cultivars. Accordingly, 371 landraces and 266 released cultivars in Henan Province were genotyped by a 660 K microarray and phenotyped for adult plant resistance (APR) to PM from 2017 to 2020, and these datasets were used to conduct multilocus genome-wide association studies (GWASs).

Results: Thirty-six varieties showed stable APR in all the environments, and eleven quantitative trait nucleotides (QTNs) were found by multiple methods across multiple environments and best linear unbiased prediction (BLUP) values to be significantly associated with APR. Among these stable QTNs, four were previously reported, three were newly discovered in this study, and the others need to be further investigated. The major and newly discovered QTN, Qpm-3BL, was located at chr03BL_AX-109,052,670, while another newly discovered QTN, Qpm-1BL, was located between chr01BL_AX-108,771,002 and chr01BL_AX-110,117,322. Five and eight landraces were identified to be resistant based on Qpm-1BL (haplotype TC) and Qpm-3BL (allele T), respectively. To validate Qpm-3BL, a new kompetitive allele-specific PCR (KASP) marker was developed to scan 155 F₂ individuals, and the average resistance score supported the value of Qpm-3BL in marker-assisted breeding. Near Qpm-3BL, PmBMYD was identified by KEGG, gene expression and comparative genomics analyses to be a candidate. Its resistance mechanism may involve gene tandem repeats.

Conclusions: This study reveals a previously unknown gene for PM resistance that is available for marker-assisted breeding.