Potential suppression of broad-spectrum virulence of Blumeria graminis f. sp. tritici population to race-specific resistance genes in hexaploid wheat

Abstract

Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt), is one of the serious diseases that attack wheat plants during the growing season. The Bgt virulence was screened against 16 Egyptian wheat cultivars and 21 powdery mildew differential lines carrying different (Pm) resistance genes in two regions (Kafr-Elsheikh and El-Minya) in Egypt 2021–2022. Broad-spectrum virulence and high diversity were observed at both regions. Regional populations of Bgt in Egypt are independent of each other. Genes, Pm2a, Pm3a, Pm1b, Pm3b, Pm21, Pm34, Pm36, Pm37, Pm53, PmNCA6, PmMIAG12, and PmNCAG13 were nationally effective, while Pm4a, Pm4b, Pm6, and Pm8 appeared to be defeated throughout the country affected by broad-spectrum virulence. Field responses showed that only four cultivars, Misr-1, Misr-2, Sakha-95 and Shandweel-1 were resistant in both regions. A strong correlation was recorded between FDS and AUDPC which implies that wheat pathologists and breeders may be able to assess their lines by a single scoring at an appropriate time. Phenotypic and genotypic data proved that ineffective Pm8 was present in four susceptible cultivars, Sakha-93, Sakha-94, Gemmeiza-10, and Gemmeiza-11, while it was present in combination with effective Pm3a in two resistant cultivars, Sakha-95 and Shandweel-1. This suggests that cultivar susceptibility may be attributed to the existence of ineffective gene Pm8 potentially suppressed by effective Pm3a in hexaploid-resistant wheat. Pyramiding effective resistance genes particularly those that have a suppression effect like Pm3a may be a viable option to avoid the risk of broad-spectrum Bgt virulence at a regional scale.