Mapping of the powdery mildew-resistance gene PmPh-3A in a new wheat-Psathyrostachys huashanica Keng introgression line

Powdery mildew is a globally devastating fungal disease that threatens the security production of wheat. The most effective way to control this disease is genetic resistance. Continuous exploration of novel resistance genes will enrich the genetic diversity of wheat breeding for powdery mildew resistance. P. huashanica is a valuable resource for developing resistance to multiple diseases. Few wheat-P. huashanica-derived lines resistant to powdery mildew have been reported. In this study, a wheat-P. huashanica introgression line, H3-5-9-3-1-4, exhibited high powdery mildew resistance at both the adult and seedling stages compared with its susceptible parent 7182. Cytological observations indicated that H3-5-9-3-1-4 had 42 chromosomes. Genomic in situ hybridization analysis using the genomic DNA of P. huashania as probe exhibited no green fluorescence signal in the root tip cells of H3-5-9-3-1-4. Four SSR markers (Xcfa2147, Xgwm429, Xbarc139 and Xgwm369) successfully amplified specific bands in P. huashanica and H3-5-9-3-1-4, which were absent in wheat parent 7182. These results indicated that H3-5-9-3-1-4 contained partial alien DNA sequence from P. huashanica and was a wheat-P. huashanica introgression line. Furthermore, inheritance analysis and gene mapping were performed using F₂ and F_2:3 populations derived from the cross between H3-5-9-3-1-4 and a mildew-susceptible cultivar Mingxian169. The resistance of H3-5-9-3-1-4 was controlled by a single dominant gene, temporarily designated PmPh-3A. Bulked segregate analysis using a 660 K SNP array revealed the SNPs were mainly enriched within an interval of 5–15 Mb on the short arm of chromosome 3A. Through genotyping the F₂ population using SSR markers, we narrowed the PmPh-3A into an interval of 4.65 Mb (7,215,576–11,861,282 bp) based on the IWGSC Chinese Spring reference genome v2.1. PmPh-3A may be a new gene for powdery mildew resistance. One hundred and twenty-six genes with high confidence were found in the target interval. Among them, 14 genes were annotated as disease-related protein genes. The identification of PmPh-3A as a novel powdery mildew resistance gene derived from P. huashanica, along with the closely linked molecular markers, provides a valuable genetic resource and may accelerate the development of resistant wheat varieties via marker-assisted selection.