Quantitative trait loci for resistance to Pyrenophora tritici-repentis race 1 in a Chinese wheat.

Tan spot, caused by Pyrenophora tritici-repentis, is an economically important foliar disease of wheat worldwide. Eight races of the pathogen have been characterized on the basis of their ability to cause necrosis or chlorosis in a set of differential wheat lines. Race 1 produces two host-selective toxins, Ptr ToxA and Ptr ToxC, that induce necrosis and chlorosis, respectively, on leaves of sensitive wheat genotypes. A population of recombinant inbred lines was developed from a cross between Chinese landrace Wangshuibai (resistant) and Chinese breeding line Ning7840 (highly susceptible) to identify chromosome regions harboring quantitative trait loci (QTL) or genes for tan spot resistance. Plants were inoculated at the four-leaf stage in a greenhouse and percent leaf area diseased was scored 7 days after inoculation. Two QTL for resistance to race 1 were mapped to the short arms of chromosomes 1A and 2B in the population. The QTL on 1AS, designated as QTs.ksu-1AS, showed a major effect and accounted for 39% of the phenotypic variation; the QTL on 2BS, designated as QTs.ksu-2BS, explained 4% of the phenotypic variation for resistance. A toxin infiltration experiment demonstrated that both parents were insensitive to Ptr ToxA, suggesting that the population was most likely segregating for reaction to chlorosis, not necrosis. The markers closely linked to the QTL should be useful for marker-assisted selection in wheat-breeding programs.