Powdery mildew is a key airborne foliar disease of barley in southeastern and southwestern China. Barley varieties usually partially or wholly lose resistance to the pathogen Blumeria graminis (DC.) f. sp. hordei (Bgh) three to five years after release due to the frequent acquirements of new virulences in the pathogen population. However, no Bgh virulence detection has been carried out in the recent decade, and thus no information is available on the present virulence components and major pathotypes in epidemic regions. Twenty-one near-isogenic lines (NILs) of Pallas were selected to detect Bgh virulence variation, with 97 pathotypes identified from the isolates collected from 2015 to 2019. The virulence complexities ranged from one to 12, with 1.5 isolates on average assigned per pathotype, suggesting a natural trait of high pathotype diversity and low virulence complexity (VC) in the Chinese Bgh populations. Eleven high virulence pathotypes were detected in the traditional barley-growing regions in Yunnan and Zhejiang. Six virulent pathotypes to resistance gene mlo-5 were detected only in the two traditional epidemic regions, with a virulence frequency (VF) of 4.8% (7/147). Compared to the results from a decade ago, VFs for resistance alleles Mla3, mlo-5, Mla6 + Mla14, Mla7 + Mlk, Mlg + MlCP, and Mla13 + MlRu3 + MlaRu4 increased from zero to 0.7 to 25.8%. Isolates from Yunnan and Zhejiang had similar virulence profiles, which differed from those identified in Tibet. In addition, genetic diversities differed in the isolate groups collected from Tibet, Yunnan, and Zhejiang.

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