Location: Plant Science ResearchTitle: Identification of Pm8 Suppressor at Pm3 Locus in Soft 1 Red Winter Wheat Author
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2012
Publication Date: 10/10/2012
Citation: Hao, Y., Chen, Z., Wang, Y., Bland, D., Parks, W.R., Cowger, C., Johnson, J. 2012. Identification of Pm8 Suppressor at Pm3 Locus in Soft 1 Red Winter Wheat. Crop Science. 52:2483-2445. Interpretive Summary: A segment of a rye chromosome previously introduced into wheat possesses the Pm8, Yr9, Lr26, and Sr31 genes for resistance to several major fungal pathogens of small grains. However, although wheat lines with this "1BL.1RS" rye segment should be resistant to strains of wheat powdery mildew against which the Pm8 resistance gene is effective, not all are. Certain wheat lines, such as AGS2000, possess Pm8 but apparently also contain a suppressor gene that renders Pm8 ineffective. To study the genetics of this suppression, a population of lines was used from the cross of AGS 2000 with another 1BL.1RS line called Pioneer 26R61, in which Pm8 is effective. Based on its location on chromosome 1A, the suppressor gene appeared to be the powdery mildew resistance gene Pm3a, confirming previous findings. In addition, the study identified another gene on wheat chromosome 7AL, contributed by Pioneer 26R61, that provides effective resistance to powdery mildew in this population. Molecular markers close to this 7AL gene were identified, but the gene remains to be characterized.
Technical Abstract: The 1BL.1RS wheat-rye translocation possesses the Pm8, Yr9, Lr26, and Sr31 genes for resistance to several major fungal pathogens of small grains. However, not all wheat cultivars with the 1RS translocation are resistant to Pm8-avirulent isolates of Blumeria graminis f. sp. tritici (Bgt), the causal pathogen of wheat powdery mildew. A suppressor is postulated to limit the function of Pm8 in certain genetic backgrounds, such as ‘AGS 2000’. To illustrate the genetic basis of the suppressor in AGS 2000, a 178-RIL population was used by crossing AGS 2000 with another 1BL.1RS cultivar ‘Pioneer 26R61’ (Pm8-effective). A single Bgt isolate, Ken-2-5, avirulent to Pm8 and virulent to Pm3a was chosen to inoculate the entire RIL population at the seedling stage. One major QTL, QSuPm.uga-1AS, was stably detected as having an inhibiting effect on Pm8 in AGS 2000, and the QTL was postulated to be Pm3a based on its location. Further evidence of the Pm8-suppressing nature of Pm3a was obtained when eight lines from the 2010 Gulf Atlantic Wheat Nursery were inoculated with Ken-2-5. The eight lines all have Pm8 (1BL.1RS), but were susceptible, as they also have Pm3a. In addition, a functional locus, QPm.uga-7AL, was identified in Pioneer 26R61, where it accounted for up to 41% of phenotypic variation in resistance to isolate Ken-2-5. QPm.uga-7AL was flanked by SSR markers Xcfa2257and Xwmc525 on 7AL, and its relationship with other known Pm loci on this chromosome arm remains uncertain.