Genetic Mapping of UM15: A Triticum Neglecta-Derived Powdery Mildew Resistance Gene On Chromosome 7AL in Common Wheat.

Powdery mildew, caused by Blumeria graminis DC f. sp. tritici, is a major fungal disease of wheat (Triticum aestivum L.) in cool and humid climates.  Race-specific host plant resistance is a reliable, economical, and environmentally benign form of disease prevention.  The identification of molecular markers tightly linked with single major resistance genes can facilitate marker-assisted selection and enable breeders to pyramid several major genes for powdery mildew resistance into a single cultivar, thereby increasing the durability of race specific sources of disease resistance. The wheat germplasm line NC09BGTUM15 (NC-UM15) possesses the first form of powdery mildew resistance introgressed from Aegilops neglecta Req. ex Bertol.  Greenhouse and field evaluation of F_2:3 families derived from a cross between NC-UM15 and the susceptible cultivar ‘Saluda’ indicated that a single dominant gene conferred resistance to powdery mildew.  Bulked segregant analysis showed that several simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers specific to chromosome arm 7AL segregated with the resistance gene.  Three SNP and four SSR markers were closely linked to the UM15 resistance gene on chromosome 7AL.  The most likely order was Xwmc525/s8057 -0.7 cM-Xcfa2257–0.4 cM–resistance gene–0.8 cM-Xcfa2240–2.8 cM–Xmag2185-3.4cM-s2929-5.4 cM-s4434.  The multi-allelic Pm1 locus and several other temporarily designated genes map to this region of chromosome 7AL.  Detached leaf tests conducted with 21 powdery mildew isolates revealed that NC-UM15 has different disease response pattern from genotypes carrying Pm37, five temporarily designed genes in the area, and all alleles of the Pm1 complex.  The UM15 resistance gene is most likely a novel source of powdery mildew resistance, however, further detached leaf and allelism tests with Pm1 and temporarily designated genes will be required to elucidate the relationship between UM15 and other Pm loci in this complex region of 7AL.