Genetic Diversity Analysis Of Blumeria Graminis F.Sp. Tritici And Mapping Of The Gene For Resistance To Powdery Mildew In The Wheat Cultivar Liangxing99

Worldwide, wheat powdery mildew is a widespread disease caused by Blumeriagraminis f. sp. tritici (Bgt). This fungus can infect wheat throughout the entiregrowing period of wheat, resulting in serious economic losses in wheat production inChina and many other parts of the world. Currently, powdery mildew is epidemic inalmost all the wheat producing regions in China. The development of resistantcultivars is one of the important measures to control wheat powdery mildew. In orderto understand the genetic diversity of Bgt from wheat fields of Shandong and Hebeiprovinces and localize the resistance gene in the wheat cultivar Liangxing99, thisstudy was carried out (1) to analyze genetic diversity of41Bgt isolates collected fromShandong and Hebei provinces in2011; and (2) to determine the effectiveness andlocalize the gene for resistance to powdery mildew in the wheat cultivar Liangxing99using57Bgt isolates and molecular marker analysis. The main findings are asfollows:1. The virulence frequencies of isolates tested ranged from0.35to0.74. Themean virulence frequency of isolates from Shandong province was not significantlydifferent from that of the isolates from Hebei province. None of the isolates testedwas virulent on Pm24carried by the Chinese landrace Chiyacao. A few isolates werevirulent on Pm1c, Pm16, Pm20, PmH, and Mlxbd. Two isolates from Handan andHuanghua of Hebei province were virulent on Pm21, but none of the isolates fromShandong province was virulent on Pm21. Analysis of genetic diversity indicated thatthe genetic variation of Bgt isolates occurred within the population, and gene flowoccurred among isolates. The polymorphism of virulence patterns on variousresistance genes was not necessarily consistent with the DNA polymorphism asrevealed by SSR markers.2. Seedling tests with57Bgt isolates indicated that Liangxing99show a broadspectrum resistance against powdery mildew. To identify the powdery mildewresistance gene in Liangxing99, molecular mapping was conducted using the F2populations and F2:3families derived from the crosses of Liangxing99and thesusceptible cultivar Zhongzuo9504. Genetic analysis demonstrated that a singledominant gene, tentatively designated MlLX99, conferred the resistance in Liangxing99to the Bgt isolate E09. The results of molecular mapping indicated that this genewas located on the long arm of chromosome2B and flanked by Xgwm120and XBE604758at genetic distances of2.9cM and5.5cM, respectively. This gene is notsimilar to the positions of loci Pm6, Pm33, PmJM22, and MlZec1. MlLX99wasdifferent from Pm6and Pm33in reactions to28and32isolates. These resultsindicated that MlLX99is most likely a new gene.