Race specific resistance to powdery mildew in Scandinavian wheat cultivars, breeding lines and introduced genotypes with partial resistance

P>Powdery mildew, caused by Blumeria graminis f. sp. tritici, is an important bread wheat (Triticum aestivum L.) disease that is favoured by the temperate Scandinavian climate. A total of 38 lines, comprising the current spring and winter wheat cultivars in Norway, various breeding lines and introduced sources of partial resistance were evaluated for race-specific resistance at the seedling stage. Various resistance genes were postulated from the reaction patterns of lines with known genes tested against 20 differential isolates in detached leaf assays. Detection of the Pm8 gene and alleles at the Pm3 locus were further aided by specific PCR primers. The most frequently present resistance genes were Pm8, followed by Pm5a, Pm3d, Pm3f, Pm3b and Pm2. Several lines were susceptible to all isolates at the seedling stage, but were known to possess high levels of partial resistance in the field; these included the German spring wheats 'Naxos' and 'Paros' and the Swedish winter wheats 'Folke' and 'Mj circle divide lner'. These lines represent highly valuable sources of partial and potentially durable resistance to powdery mildew.