Marker Development and Saturation Mapping of the Tan Spot Ptr ToxB Sensitivity Locus Tsc2 in Hexaploid Wheat

Ptr ToxB is a host-selective toxin produced by the tan spot fungus, Pyrenophora tritici-repentis, that induces chlorosis in wheat lines harboring the Tsc2 gene, which was previously mapped to chromosome arm 2BS in tetraploid wheat (Triticum turgidum L.). In this study, molecular mapping in a recombinant inbred line (RIL) population derived from the Ptr ToxB-sensitive 'Katepwa' and the Ptr ToxB-insensitive landrace Salamouni (Salamouni x Katepwa [SK] population) confirmed the location of Tsc2 on 2BS in hexaploid wheat (Triticum aestivum L.). Analysis of an F 2 population derived from the same parents indicated that a single dominant gene governed Ptr ToxB sensitivity. Thirteen microsatellite markers were used to construct a basic linkage map of the Tsc2 region in the SK population, and 14 additional markers developed from bin-mapped expressed sequence tags (ESTs) and from ESTs identified based on colinearity with rice (Oryza sativa L.) and Brachypodium distachyon (L.) P. Beauv. were mapped to the Tsc2 region. Tsc2 was delineated to a 3.3 cM interval and cosegregated with marker XBE444541. Spore inoculations and composite interval-regression mapping demonstrated that a compatible Tsc2-Ptr ToxB interaction accounted for 54% of the variation in disease expression. Analysis of Ptr ToxB-sensitive and-insensitive genotypes suggested that XBE444541 is diagnostic for Tsc2 and should be useful for marker-assisted selection.