GENETICS OF TAN NECROSIS AND EXTENSIVE CHLOROSIS IN TAN SPOT OF WHEAT CAUSED BY PYRENOPHORA-TRITICI-REPENTIS

Pyrenophora tritici-repentis (Ptr) induces tan necrosis and/or chlorosis, including extensive chlorosis in differential wheat cultivars. Reciprocal crosses were made in all combinations between the hexaploid wheats Glenlea (necrotic only), 6B365 (chlorotic only), and Salamouni (non-necrotic, nonchlorotic). F1, F2, and F3 progenies were sequentially tested for extensive chlorosis by using isolate D308 (nec-chl+) and for tan necrosis with isolate 86-124 (nec+chl-) and/or the Ptr necrosis toxin. Reciprocal effects were not observed throughout the study. Resistance to tan necrosis and insensitivity to the Ptr necrosis toxin were recessive. Resistance to extensive chlorosis was dominant and incompletely dominant in crosses of line 6B365 with Glenlea and Salamouni, respectively. The F2 and F3 segregation ratios were consistent with the action of two independent genes, one controlling the development of tan necrosis, the second controlling the development of extensive chlorosis.