Abstract: 【Objective】Powdery mildew, caused by Blumeria graminis f. sp.tritici (Bgt), is an important disease that causes substantial yield losses in wheat (Triticum aestivum L.) in China, there is a great significance for using resistance genes to control this disease. Powdery mildew resistance gene Pm21, transferred from Haynaldia villosa by a 6VS/6AL translocation, confers durable and broad-spectrum resistance to the disease. This study is to develop gene specific PCR marker, analyze the distribution of Pm21 in China winter wheat regions, and to provide a theoretical basis and technical support for reasonable arrangement and marker-assisted selection for Pm21.【Method】Based on the sequence of Stpk-V gene which was cloned and related to the resistance pathway (GenBank accession number: HQ864471.1), the protein sequences were extracted and the conservative start-stop sites were analyzed by Pfam software, in order to amplify this gene specifically, the marker WS-1 was developed excluding conserved domain. For constructing an F2 populations derived from susceptible cultivar Avocet S and the lines 92R137 carrying Pm21, infection types in F2 plants were evaluated by artificial inoculation with isolate E09 during seedling stage, F2 plants were amplified by WS-1, and the testing results and infection types were analysed to confirm the accuracy of WS-1. A total of 662 wheat cultivars and breeding lines growing in different winter wheat regions in China were detected by WS-1 to analyze the distribution of Pm21, and the materials carrying Pm21 were further tested the resistance to powdery mildew under field conditions. In order to further prove the accuracy of WS-1, the marker NAU/xibao15902 developed by Cao Aizhong and others was used to amplify the lines with Pm21 and without Pm21 (50 samples from each type). 【Result】 As a dominant molecular marker, WS-1 could be amplified a 949 bp fragment in the lines with Pm21 on 8% non-denaturing polyacrylamide gel, but did not in the lines without Pm21. The 377 F2 populations segregated 286 resistant﹕91 susceptible fitting the 3﹕1 ratio, which indicated that Pm21 presents a single dominant gene, and the testing results by WS-1 were consistent with infection types. There were 49 lines showed positive strand in 662 lines, and the average distribution frequency of Pm21 gene was 7.4%; the lines containing Pm21 in Southwestern Winter Wheat Region, Northern China Plain Winter Wheat Region, Yellow and Huai Valley Facultative Wheat Region and Middle & Lower Yangtze Valley Winter Wheat Region were 33, 4, 9, and 3, and their frequencies were 34.4%, 5.3%, 3.1% and 1.5%, respectively.【Conclusion】WS-1 can be detected wheat cultivars and breeding lines which carry Pm21 accurately, also can be applied to the gene pyramiding breeding in the future. The distribution of Pm21 in winter wheat regions is different, the risk of pathogen directional selection will be promoted because of the high frequency of Pm21 gene in wheat cultivars of Sichuan and Guizhou provinces, and we should pay more attention to it in wheat breeding.

Key words: wheat , powdery mildew , Pm21 , gene-specific PCR marker , durable resistance of genes