Abstract:

Xiaobaidong, a Chinese landrace, is proved to be resistant to powdery mildew (Blumeria graminis DC f. sp. tritici) with wide spectrum of resistance to pathogen races, especially effective to current prevalent races. This variety shows a response pattern that is different from the variety possessing documented Pm genes after inoculation with 10 isolates of different virulence. Genetic analysis indicated that a single recessive gene was responsible for the powdery mildew resistance at seedling stage. To detect the adjacent molecular markers of the gene, we constructed two mapping populations derived from the reciprocal crosses between Xiaobaidong and a susceptible cultivar Chancellor with 125 and 107 individuals of the F₂ generation. Seedlings of F₁ and F₂ plants were inoculated with isolate E09 of B. graminis DC f. sp. tritici for powdery mildew resistance identification. Using resistant and susceptible bulks, we identified the resistance gene mlxbd between simple sequence repeat (SSR) markers Xgwm577 and Xgwm1267 on chromosome 7. The gene mlxbd was located on the distal bin of chromosome 7BL-10 (Bin 0.78-1.00) by using the Chinese Spring nullisomic-tetrasomics, ditelosomics, and deletion lines. To verify the efficiency of the SSR markers that might be used in molecular marker-assistant selection (MAS), genome DNA of 23 wheat varieties with definite resistance genes were amplifiedby Xgwm577, the proximal marker of mlxbd. The result showed that Xgwm577 was able to differentiate resistance genes originated from Chinese varieties with Pm5a and Pm5b except PmH, however, resistance genes near Pm5 locus were failed to be identified with Xgwm577. This indicates that Xgwm577 should be combined with other markers in MAS.

Key words: Wheat, Xiabaidong, Powdery mildew, Resistance gene, SSR marker