Quantitative Trait Loci for Wheat Resistance to Pyrenophora tritici-repentis in Chinese Landrace WSB.

Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is an economically important foliar disease worldwide. Multiple races of the pathogen have been reported based on their ability to cause necrosis and/or chlorosis in differential wheat lines. Race 1 produces two host-selective toxins. A recombinant inbred population was developed from cross between a landrace WSB (resistant) and a breeding line Ning7840 (highly susceptible) from China to identify genomic regions harboring quantitative trait loci (QTLs) for resistance to tan spot. Two QTLs were mapped to the distal end of the short arm of chromosome 1A and 2B in WSB/Ning7840 population. The QTL on 1AS showed a major effect on resistance to race 1 and accounted for 40% of the phenotypic variation, while the 2BS QTL showed a minor effect and explained 13% of the phenotypic variation for tan spot resistance. The major QTL on 1A was located in the same region as QTsc.ndsu-1A. The two QTLs showed an additive effect and together explained 53% of phenotypic variation for resistance to race 1.  Interaction between two QTLs was not found. Infiltration assay with toxin Ptr ToxA showed that both parents were insensitive to the toxin, suggesting the QTLs are most likely resistant to Ptr ToxC. The markers closely linked to the QTLs should be useful for introgression of the resistance QTLs into adapted wheat cultivars.