Evaluation of powdery mildew resistance in wheat cultivars and molecular detection of resistance genes in Shanxi province, China

Powdery mildew (PM) is one of the major diseases threatening wheat production worldwide. Accurate identification of powdery mildew resistance in wheat cultivars and dissection of its genetic basis are crucial for breeding and deploying disease-resistant cultivars. In this study, we evaluated seedling- and adult-plant resistance to powdery mildew in 326 wheat accessions. We then used 11 molecular markers targeting Pm genes that are commonly used in breeding or confer high levels of resistance, including Pm2b, Pm4, Pm8, and Pm21, to detect resistance alleles. To identify additional Pm loci, we also performed a genome-wide association study (GWAS) using a wheat 16K SNP array. The results showed that 10 cultivars (e.g., Jinfeng 3, Shengmai 104, and Linmai 5311) were resistant to the Bgt isolate E09, indicating an overall lack of seedling resistance among the evaluated accessions. At the adult stage, 29 cultivars (e.g., Yunhei 28, Yaomai 30, and Yunhei 14207) were resistant to mixed Bgt isolates, and only four cultivars (Shengmai 104, JT176, Linmai 5311, and Jinfeng 3) displayed good resistance at both the seedling and adult stages. Multi-isolate tests of seedling resistance further indicated that Jinfeng 3, Shengmai 104, and JT176 were highly resistant to most isolates evaluated, representing valuable germplasm for powdery mildew resistance breeding. Marker-based analysis suggested that Shanxi wheat has a narrow genetic basis for powdery mildew resistance and tends to carry only one major Pm gene. Of the 11 Pm genes assayed, seven genes (e.g., Pm2b, Pm5e, and Pm6) were detected, whereas Pm1a, Pm24, Pm60, and Pm69 were not detected. In total, 108 accessions carried only one of the tested Pm genes; Pm8 was the most frequent, occurring in 14.11% of accessions. For gene pyramiding, the most common combinations were Pm5e+Pm8 and Pm6+Pm8, and only one cultivar carried four Pm genes. GWAS identified 15 stable loci across eight chromosomes; haplotype-phenotype analyses revealed significant associations at loci on chromosomes 1A, 2D, 4B, and 6A, and loci on 2D, 4B, 7B, and 7D may harbor novel powdery mildew resistance loci.