Further Evidence Supported the Suppressor of Pm8 at Pm3 Locus in US Soft Red Winter Wheat

The 1BL.1RS wheat-rye translocation possessed Pm8, Yr9, Lr26, and Sr31 resistance genes. However, not all cultivars with 1RS translocation are resistant to Pm8-avirulent isolates of Blumeria graminis f. sp. tritici (Bgt), the causal fungal pathogen of wheat powdery mildew. A suppressor is postulated to limit the function of Pm8 in certain genetic backgrounds, such as in ‘AGS 2000’. To illustrate genetic basis of possible suppressor(s) of Pm8 in AGS 2000, 178 RILs population were developed by crossing with another 1BL.1RS cultivar ‘Pioneer 26R61’ (Pm8 effective). Single Bgt isolate named Ken-2-5 (avirulent to Pm8, virulent to Pm3a) was chosen to inoculate the whole population in the seedling stage. One major QTL QSuPm.uga-1AS was consistently identified with inhibitor effect of Pm8 in AGS 2000, and the QTL was considered as Pm3a (the putative suppressor of Pm8) based on its location. Evidence further supported the Pm3a suppressor nature of Pm8 in soft red winter wheat when 10 lines with 1BL.1RS from the 2010 Uniform Southern Soft Red Winter Wheat Nursery were inoculated with isolate Ken-2-5. Two lines were rated as susceptible and also possessed the Pm3a. The validation of another 22 lines with 1BL.1RS from the 2010 Gulf Atlantic Wheat Nursery is in progress. A functional locus QPm.uga-7AL was also identified from Pioneer 26R61 for resistance to isolate Ken-2-5 and explained up to 41% of phenotypic variation. QPm.uga-7AL was flanked by SSR markers Xcfa2257 and Xwmc525 on chromosome 7AL, and the relationship with other known Pm loci on 7AL remains uncertain.