A gene for resistance to a necrosis-inducing isolate of Pyrenophora tritici-repentis located on 5BL of Triticum aestivum cv. Chinese Spring.

Several sources of high-level resistance to tan spot caused by Pyrenophora tritici-repentis have been identified in hexaploid wheat (Triticum aestivum L.). This study was conducted to determine the number and chromosome location of a gene(s) in the cultivar Chinese Spring (CS) that confers resistance to a tan necrosis inducing isolate (nec+chl−) of P. tritici-repentis, 86-124, and insensitivity to Ptr necrosis toxin. Reciprocal crosses were made between CS (resistant-insensitive) and 'Kenya Farmer' (KF) (susceptible-sensitive). Analysis of the CS/KF F1and F2 populations and F2-derived F3 families identified a single nuclear recessive gene governing resistance to isolate 86-124 and Ptr necrosis toxin. Evaluation of the CS(KF) substitution series, F2 monosomic analysis, and screening of a series of 19 CS compensating nullitetrasomic and two ditelosomic lines (2AS and 5BL) indicated that the resistance gene was located on chromosome arm 5BL. No linkage exists between Lr18 and the tan necrosis resistance gene on chromosome arm 5BL. It is proposed that the gene for resistance to the tan necrosis inducing isolate 86-124 (nec+chl−) of P. tritici-repentis and Ptr necrosis toxin be named tsn1. Key words : wheat, Triticum aestivum L., tan spot resistance, Pyrenophora tritici-repentis (Died.) Drechs., chromosome location, Ptr necrosis toxin.