Genomic Analysis and Marker Development for Race-Specific and Nonspecific Tan Spot Resistance Genes in Wheat

Tan spot, caused by Pyrenophora tritici-repentis, is a destructive disease of wheat worldwide. The pathosystem is known to involve race-specific interactions involving host gene-necrotrophic effector interactions, such as Tsc1-Ptr ToxC, that lead to susceptibility, and also race-nonspecific resistance genes. Here, we analyzed bi-parental hexaploid populations derived from Louise × Penawawa (LouPen) and LMPG-6 × PI626573 for reaction to chlorosis induced by Ptr ToxC-producing races of the tan spot pathogen. Both populations harbored a QTL with major effects in the Tsc1 region of chromosome arm 1AS. Numerous markers were developed based on the wheat 90K SNP consensus map, SNP contextual sequences, and their corresponding whole genome survey sequences, and used to saturate the Tsc1 region of both maps delimiting the gene to a small interval. Analysis of the LouPen population revealed that it also harbored a major race-nonspecific resistance QTL on 3BL. Additional evaluation of a tetraploid population derived from Langdon (LDN) × LDN-Triticum dicoccoides disomic 3B substitution line revealed a single dominant gene on 3BL conferring resistance to all known tan spot races. This gene was mapped to a position corresponding to that of the 3BL QTL identified in the LouPen population based on common SSR markers. Genetic analysis of the 1AS and 3BL QTLs in the LouPen population indicated that their effects were largely additive. The markers identified in this research can be used to expedite the pyramiding of the 3BL race nonspecific resistance gene and the Ptr ToxC-insensitive Tsc1 allele to develop tan spot resistant wheat varieties.