Abstract: Wheat powdery mildew caused by Blumeria graminis (DC.) f. sp. tritici E.O. Speer is one of the major epidemic diseases threatening production of wheat (Triticum aestivum L.) in China. It is necessary to establish information on resistance to the disease in wheat cultivars and germplasm lines for parental selection in breeding, deployment of resistant germplasm, and application of resistant cultivars for controlling the disease. In this study, reactions to eight isolates of B. graminis (DC.) f. sp. tritici E.O. Speer were tested in commercial wheat cultivars, wheat lines involved in the national yield trials, and core collections. The presence of genes Pm4a, Pm8, and Pm21 for resistance to powdery mildew was detected using the gene-specific markers. Among 148 commercial wheat cultivars released since the 1980s, 16.9% exhibited resistance to multiple isolates, most of which were released in the 2000s. Over 50% of the cultivars released in different decades were susceptible to all the isolates tested. The frequencies of resistant cultivars from different wheat producing regions seemed to be associated with the significance of powdery mildew epidemic in a given region. Out of 1160 entries in the core collection, the proportions of entries resistant to isolate E09 were 3.4% and 4.2% in the landrace and improved cultivars, respectively. The Southwestern Autumn-Sown Spring Wheat Zone and the Xinjiang Winter-Spring Wheat Zone had higher percentages of E09-resistant cultivars than other wheat zones. None of the cultivar from the Southern Autumn-Sown Spring Wheat Zone, Northern Winter Wheat Zone, and Northern Spring Wheat Zone was resistant. The results of multiple-isolate test demonstrated that 33.7% were resistant among the 263 mini-core collection entries, most of which were resistant to one or two isolates. This indicates that there is a need to select resistant entries as recurrent parents for efficient use of existing core collection and to construct applied core collection for resistance to powdery mildew. Using the markers specific for resistance genes, the results of molecular detection demonstrated that 43.2% of the commercial cultivars contained gene Pm8. This gene was detected in the wheat lines involved in the national wheat yield trails at a high frequency. Genes Pm4a and Pm21 were detected mainly in the wheat lines or cultivars that were developed in the Yangtze River region. Some cultivars highly resistant to powdery mildew may possess other resistance genes that warrant further determination.

Key words: Wheat, Disease resistance, Powdery mildew, Resistance gene, Pm8, Pm4, Pm21