Restriction fragment length polymorphism mapping of resistance to two races of Pyrenophora tritici-repentis in adult and seedling wheat

Resistance to the chlorosis factor of tan spot of wheat, caused by the asco mycete Pyrenophora tritici-repentis, has been reported to be quantitative a nd a single quantitative trail loci (QTL), QTsc.ndsu-1A, explained 35% of t he variation for resistance to a single isolate in seedlings of recombinant inbred (RI) lines derived from the cross W-7984/Opata 85. The objectives o f this study were to determine the number and locations of genes conditioni ng resistance to the same isolate in adult plants of this population and th ree isolates in seedlings of wheal RI lines derived from the cross W-7976/T renton. An extensive restriction fragment length polymorphism map exists fo r the W-7984/Opata 85 population, and markers significantly associated (P < 0.01) with resistance to tan spot were selected to analyze the W-7976/Tren ton population. A multiple regression model accounted for 49% of the variat ion for resistance in adult plants with QTsc.ndsu-1A, explaining 26% of the variation. QTsc.ndsu-1A explained 47, 58, and 64% of the variation for res istance in seedlings to isolates Pti2, 78-62, and D308, respectively. These results showed that the QTL for tan spot resistance on chromosome IAS was effective in both seedlings and adult plants and against isolates from diff erent races of P. tritici-repentis.