Identification of specific powdery-mildew-resistance genes in individual wheat plants using the first two seedling leaves

Identification of resistance genes in individual plants requires the use of leaves that have homogeneous reactions to the pathogen. The reactions of the first two leaves of seedlings of 12 wheat differential varieties to 20 Erysiphe graminis f.sp. tritici isolates were compared using in vitro tests on detached leaf segments. The expression of resistance and susceptibility did not differ significantly between the first two leaves with the 12 resistance genes tested. Consequently, the identification of specific powdery-mildew-resistance genes in individual plants is possible if approximately 10 segments of the primary and secondary leaves are used, each of them inoculated by one out of a set of 10 differential isolates. The reaction pattern of a plant to the tester isolates is interpreted according to a procedure in two steps, that are easily computerized. Identification of resistance genes in individual plants is particularly useful for resistance studies in heterogeneous plant populations.