Inheritance and interaction of spring wheat (Triticum aestivum L.) resistance to Race 2 and Race 3 of Pyrenophora tritici-repentis (Died.) Drechs.

Abstract

Tan spot is a residue-borne leaf spotting disease caused by the fungal pathogen Pyrenophora tritici-repentis. An understanding of the inheritance of resistance is required to build a strategy for incorporating tan spot resistance into commercial cultivars of wheat. The objectives of this study were to determine the inheritance of host resistance to isolates of races 2 (a necrosis-inducing race) and 3 (a chlorosis-inducing race) of P. tritici-repentis. Crosses were made between seven wheat (Triticum aestivum) genotypes (Katepwa, BH1146, ST15, ST6, Erik, 6B1043, 6B367). Parents, F1, F2and F2-derived F3 populations were inoculated with isolates 86-124 and D308 (races 2 and 3, respectively) of P. tritici-repentis and infiltrated with Ptr ToxA. Resistance to 86-124 and insensitivity to Ptr ToxA was controlled by a single recessive nuclear gene in all of the resistant/susceptible crosses. In contrast, resistance to D308 was controlled by a single dominant nuclear gene in five crosses and two genes in two crosses. In the BH1146/ST15 cross two dominant genes controlled resistance to D308, while in the Katepwa/ST15 cross two recessive genes controlled resistance. Reactions to race 2 were independent of reactions to race 3 and controlled by independent genetic systems. Key words: Triticum aestivum L., Pyrenophora tritici-repentis (Died.) Drechs., disease resistance, inheritance, Ptr necrosis toxin, tan spot