In the progeny of a cross between the common wheat cultivar Tähti and Triticum militinae, a member of the timopheevii group of tetraploid wheats, several hybrid lines were selected that are characterized by improved seedling and adult plant resistance (APR) to powdery mildew. An F2 single-seed descendant mapping population segregating for seedling resistance and APR to powdery mildew was analysed for the identification of quantitative trait loci (QTL). The main QTL responsible for APR was detected on the long arm of chromosome 4A tightly linked to the Xgwm160 locus on a T. militinae translocation explaining up to 54% of phenotypic variance. The same translocation influenced seedling resistance to powdery mildew upon inoculation of plants with a synthetic population of Blumeria graminis DC. f. sp. tritici, and explained 28-33% of the phenotypic variance.

Introgression of several genomic loci from tetraploid Triticum militinae into bread wheat cv. Tähti has increased resistance of introgression line 8.1 to powdery mildew in seedlings and adult plants. In our previous work, only a major quantitative trait locus (QTL) on chromosome 4AL of the line 8.1 contributed significantly to resistance, whereas QTL on chromosomes 1A, 1B, 2A, 5A and 5B were detected merely on a suggestive level. To verify and characterize all QTLs in the line 8.1, a mapping population of double haploid lines was established. Testing for seedling resistance to 16 different races/mixtures of Blumeria graminis f. sp. tritici revealed four highly significant non-race-specific resistance QTL including the main QTL on chromosome 4AL, and a race-specific QTL on chromosome 5B. The major QTL on chromosome 4AL (QPm.tut-4A) as well as QTL on chromosome 5AL and a newly detected QTL on 7AL were highly effective at the adult stage. The QPm.tut-4A QTL accounts on average for 33-49 % of the variation in resistance in the double haploid population. Interactions between the main QTL QPm.tut-4A and the minor QTL were evaluated and discussed. A population of 98 F(2) plants from a cross of susceptible cv. Chinese Spring and the line 8.1 was created that allowed mapping the QPm.tut-4A locus to the proximal 2.5-cM region of the introgressed segment on chromosome 4AL. The results obtained in this work make it feasible to use QPm.tut-4A in resistance breeding and provide a solid basis for positional cloning of the major QTL.

No abstract

Common wheat cv. Meri was crossed to a set of 21 Chinese Spring monosomic lines to characterize resistance to powdery mildew and to determine the chromosomal location of the gene(s). Monosomic F1 plants were allowed to self-pollinate and to produce F2 seeds. Seedlings of F2 and F3 plants and their parents were inoculated with isolates Ns 2 and 9 of Erysiphe graminis f. sp. tritici. Analysis of obtained data revealed that one major dominant gene conferring resistance is located on chromosome 1B of cv. Meri. The new gene is designated by symbol Pm28. On the basis of the trivalent configuration frequency (without univalent) at the 1st metaphase of meiosis it was found that two reciprocal translocations involving chromosomes 2A/5A and 5B/5D differentiate cv. Meri from cv. Chinese Spring. In the F1 monosomic hybrids, genes causing a decrease in pairing are found on chromosomes 4D and 6D, and genes enhancing pairing--on chromosomes 3A and 7B.

No abstract