Molecular Mapping Of The Genes For Resistance To Powdery Mildew In The Wheat Cultivars Liangxing99and Wennong14

Powdery mildew (caused by Blumeria gramins f. sp. tritici, Bgt) is an importantdisease of wheat (Triticum aestivum L.) in the world, which causes heavy losses inwheat production. The best way to reduce the economic loss is the use of cultivarsresistant to powdery mildew. The identification of resistant sources is essential indeveloping resistant cultivars. The objectives of this study were to map the genes forresistance to powdery mildew in the wheat cultivars Liangxing99and Wennong14,to develop molecular markers that can be used in molecular marker-assisted selection,and to determine the usefulness of these genes.Liangxing99, a widely grown commercial cultivar in northern China, carries asingle dominant gene, MlLX99, for resistance to powdery mildew. This gene waspreviously mapped to the deletion bin2BL2-0.36-0.50. To saturate the geneticlinkage map of MlLX99, comparative genetic mapping was performed, resulting in8linked markers derived from the sequences of bin-mapped ESTs from wheat and/orthe gene sequences located in the collinear chromosomal region of barley (Horderumvulgare). The flanking markers Xics34and Xics30were0.3and0.8cM away fromMlLX99, respectively. Results of disease assessments indicated that Liangxing99wasresistant to75(81.5%) isolates out of92Bgt isolates originating from northern Chinaand the reaction patterns of MlLX99to the Bgt isolates tested were different from thewheat cultivars carrying genes Pm6(Coker747), Pm33(2632-32R), and PmJM22(Jimai22), which were previously mapped to the distal part of chromosome2BL.Based on its unique position on chromosome arm2BL, MlLX99represents a newlocus in the deletion bin2BL2-0.36-0.50of chromosome arm2BL and was officiallydesignated Pm52.Wennong14is a facultative wheat cultivar commercialized in Shandongprovince and the neibouring provinces in the northern part of Yellow and Huai RiverValleys Facultative Wheat Zone in China. In the present study, a set of Bgt isolatesand a mixture of isolates were used to test the resistance of Wennong14to powderymildew at the seedling stage. Among the52Bgt isolates tested, Wennong14wasresistant to41isolates and susceptible to11isolates. The virulence pattern of theseBgt isoaltes on Wennong14was similar as the known powdery mildew resistance gene Pm2, but Wennong14differed from Pm2in the reactions to5Bgt isolates.Wennong14was highly resistant to a mixture of Bgt isolates at the adult plant stage.Using the F2and F2:3segregation populations developed from the cross betweenWennong14and Han4564, genetic analysis demonstrated that the resistance againstthe Bgt isolate E09was controlled by a single dominant gene, designated PmW14.Based on the results of molecular analysis, PmW14was linked to markers Xcfd8,Xcfd81, and SCAR203with genetic distances of7.5,1.8, and7.7cM, respectively.Because these markers were previously localized on wheat chromosome5DS in thedeletion bin of5DS-1-0-0.63and linked to gene Pm2, PmW14was most likely anallele in locus Pm2.