Genetic Analysis of Partial Resistance to Powdery Mildew in Bread Wheat Line Saar

Powdery mildew, caused by Blumeria graminis (syn. Erysiphe graminis) f. sp. tritici, is an important disease of bread wheat (Triticum aestivum) in many countries. The CIMMYT bread wheat line Saar has exhibited a high level of partial resistance to powdery mildew in field trials conducted in Europe, Asia, and South America, and represents a valuable source of resistance in wheat breeding. A set of 114 random F₅ inbred lines from the cross Saar × Avocet-YrA (susceptible) were evaluated in replicated field trials at two locations in southeastern Norway to determine the number of genes involved in partial resistance to powdery mildew. Narrow-sense heritability estimates were high (0.83 to 0.92). Based on both quantitative and qualitative genetic analyses, the minimum number of genes with additive effects segregating for powdery mildew resistance in the population was four. Transgressive segregation indicated that Avocet-YrA might have contributed one minor gene for resistance. It is concluded that partial resistance to powdery mildew in Saar is controlled by at least three genes. Such resistance conferred by multiple genes having additive effects is expected to be durable.