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

Abstract

Ptr ToxB is a host-selective toxin produced by the tan spot fungus,Pyrenophora tritici-repentis, that induces chlorosis in wheat linesharboring the Tsc2 gene, which was previously mapped to chromosome arm2BS in tetraploid wheat (Triticum turgidum L.). In this study, molecularmapping in a recombinant inbred line (RIL) population derived from thePtr ToxB-sensitive `Katepwa' and the Ptr ToxB-insensitive landraceSalamouni (Salamouni x Katepwa {[}SK] population) confirmed the locationof Tsc2 on 2BS in hexaploid wheat (Triticum aestivum L.). Analysis of anF 2 population derived from the same parents indicated that a singledominant gene governed Ptr ToxB sensitivity. Thirteen microsatellitemarkers were used to construct a basic linkage map of the Tsc2 region inthe SK population, and 14 additional markers developed from bin-mappedexpressed sequence tags (ESTs) and from ESTs identified based oncolinearity with rice (Oryza sativa L.) and Brachypodium distachyon (L.)P. Beauv. were mapped to the Tsc2 region. Tsc2 was delineated to a 3.3cM interval and cosegregated with marker XBE444541. Spore inoculationsand composite interval-regression mapping demonstrated that a compatibleTsc2-Ptr ToxB interaction accounted for 54% of the variation in diseaseexpression. Analysis of Ptr ToxB-sensitive and-insensitive genotypessuggested that XBE444541 is diagnostic for Tsc2 and should be useful formarker-assisted selection.