Resistance gene deployment and pyramiding shape powdery mildew resistance in 204 contemporary Chinese wheat cultivars

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), remains a major constraint to global wheat production, necessitating the effective deployment of resistance genes adapted to evolving pathogen populations. In this study, seedling stage resistance was evaluated in 204 Chinese wheat cultivars using two Bgt isolates (A13 and E09) and a mixed inoculum (MX) representing heterogeneous pathogen pressure. Marker-based assays detected nine powdery mildew resistance (Pm) genes, and associations between gene presence and resistance were analyzed using logistic regression models. Resistance frequencies were 23.0% and 24.0% against A13 and E09, respectively, but only 11.8% against MX, highlighting limited broad-spectrum resistance in current germplasm. Gene frequencies varied widely, with Pm8 being the most common (27.0%), followed by Pm34 (19.6%), Pm52 (17.2%), and Pm2 (14.7%), whereas Pm21 occurred in only 1.5% of cultivars and Pm35 was not detected. Regression analyses revealed that Pm2 and Pm34 consistently conferred resistance across all inocula, while several other genes exhibited isolate-dependent or nonsignificant effects. Resistance probability increased significantly with the number of Pm genes, with odds ratios increasing 2.09-, 2.41-, and 2.94-fold per additional detected gene for A13, E09, and MX, respectively. Cultivars harboring three or more Pm genes exhibited resistance frequencies exceeding 50%, whereas cultivars lacking detected genes exhibited ≤12% resistance. These findings demonstrate that resistance effectiveness in contemporary wheat germplasm increases with the number of detected Pm genes and is enhanced by pyramiding complementary resistance genes. The observed benefits of gene pyramiding support its use as a breeding strategy for achieving broader and potentially more durable resistance under diverse pathogen pressures.