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 P yrenophora tritici-repentis in susceptible hexaploid wheats (Triticum aesti vum). To date, five races of the pathogen have been identified based on vir ulence patterns on a differential set of wheat genotypes. The inheritance o f wheat reaction to three races of P. tritici-repentis, races 2, 3 and 5, a nd to the toxins Ptr ToxA and Ptr ToxB produced by races 2 and 5, respectiv ely, was determined. Race 2 and Ptr ToxA induce necrosis on susceptible hos t 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 BC1 F2 progeny were evaluated for reaction to the appropriate races and/or path ogen-produced toxins. No segregation was observed in all crosses between re sistant lines. Three independently inherited loci were identified, each loc us controlling the reaction to a single race. Susceptibility (necrosis or c hlorosis) was dominant for all three loci identified in this study. Sensiti vity to Ptr ToxB produced by race 5 and susceptibility to race 5 were found to be controlled by the same locus.