Molecular Mapping of a New Powdery Mildew Resistance Gene in Wheat Cultivar AGS 2000

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is an important disease of common wheat (Triticum aestivum L.) in southeastern USA. It decreases both yield level and quality grade. To limit the negative impacts, powdery mildew resistance genes have been added into commercial wheat cultivars, however for some of the resistance genes, their identities remain unclear in certain genotypes, such as AGS 2000. In the present study, genetic analysis of the resistance in AGS 2000 was carried out in a RIL population from a cross between Pioneer^® variety 26R61 and AGS 2000. Phenotypic evaluation was conducted in two independent growth chambers with the inoculation of Bgt isolate #Plains, which was collected in 26R61 plants in the field in Plains, GA, and purified from a single-colony. A major QTL designated QPm.uga-6BL was subsequently identified from AGS 2000 on the long arm of chromosome 6B and situated between markers wPt-9256 and Xbarc134 but closely linked with the latter at 1.2 cM. The QTL can explain most part of the phenotypic variation (up to 78%), and also has highly significant LOD values. We proposed a simple Mendelian factor controlled the resistance in AGS 2000 for the current Bgt isolate and temporarily designated it as PmA2K. Since there is no known powdery mildew resistance gene on this particular location in common wheat, PmA2K should represent a new source of powdery mildew resistance. The application of the closely linked marker in marker-assisted selection was also addressed.