Race structure of Pyrenophora tritici-repentis isolates obtained from wheat in South America

Abstract

Knowledge of genetic variation in a pathogen population contributes to breeding for disease resistance. The fungus Pyrenophora tritici-repentis, cause of tan spot of wheat, is an important foliar pathogen worldwide. Currently, eight races have been identified in the fungal population prevalent on wheat and alternative hosts. Races 1 through 6 have been observed in North America. However, the fungal population from South America has not been characterized as to race. In this study, 48 single-spore isolates of P. tritici-repentis, recovered from wheat, were obtained from Argentina (10), Brazil (23), and Uruguay (15). Isolates were tested by inoculating individually on 2-leaf stage seedlings of the wheat differentials Glenlea, Katepwa, ND495, 6B365, M-3, and Salamouni in the greenhouse. They were grouped into different races based on necrosis and chlorosis induction on the differentials. Isolates from Argentina were grouped into races 1 and 7; from Brazil into races 1 and 8; and, from Uruguay into races 1 and 2. Results indicate that P. tritici-repentis has a diverse population on wheat in South America. More isolates are under investigation to obtain a comprehensive virulence pattern of the pathogen population in South America. Wheat lines should be screened against all known races to achieve durable resistance in a cultivar release program. The P. tritici-repentis race structure on wheat in Europe needs to be determined, as the pathogen has become a concern for wheat breeders and pathologists.

Genetics and breeding for resistance against four leaf spot diseases in wheat (Triticum aestivum L.)

“…The distribution of the genes encoding three different NEs (ToxA, ToxB and ToxC) and the wheat genotypes with corresponding S genes involved in interactions differs widely in different parts of the world. Of these, ToxA is the most widely distributed, present in ~80% of the world’s Ptr isolates ( Lamari et al., 1998 ; Ali and Francl, 2002 ; Friesen et al., 2006 ).…”