Inheritance of race-specific necrotic and chlorotic reactions induced by Pyrenophora tritici-repentis in hexaploid wheats

Tan necrosis and extensive chlorosis are two distinct symptoms induced by Pyrenophora tritici-repentis in susceptible hexaploid wheats (Triticum aestivum). To date, five races of the pathogen have been identified based on virulence patterns on a differential set of wheat genotypes. The inheritance of wheat reaction to three races of P. tritici-repentis, races 2, 3 and 5, and to the toxins Ptr ToxA and Ptr ToxB produced by races 2 and 5, respectively, was determined. Race 2 and Ptr ToxA induce necrosis on susceptible host plants while race 3, race 5, and Ptr ToxB induce chlorosis. Crosses were made among seven hexaploid wheat genotypes and the F-1, F-2, BC1F1, and BC1F2 progeny were evaluated for reaction to the appropriate races and/or pathogen-produced toxins. No segregation was observed in all crosses between resistant lines. Three independently inherited loci were identified, each locus controlling the reaction to a single race. Susceptibility (necrosis or chlorosis) was dominant for all three loci identified in this study. Sensitivity to Ptr ToxB produced by race 5 and susceptibility to race 5 were found to be controlled by the same locus.