Pyrenophora tritici-repentis causes tan spot of wheat worldwide. Fungal isolates have been characterized into seven races based on their ability to induce necrosis and chlorosis on appropriate wheat differentials (1,2). Nineteen single-spore isolates of P. tritici-repentis were recovered from diseased wheat leaves collected from Brazil. The isolates were tested for their race structure by individually inoculating a suspension of 3,000 conidia per ml on wheat differential seedlings at the 2-leaf stage in the greenhouse. The isolates were tested three times and consistent results were found. The differential set was comprised of Glenlea, Katepwa, ND495, 6B365, Salamouni, and M-3. Seven of the 19 isolates were grouped into race 1 because they produced necrosis on Glenlea, Katepwa, and ND495; chlorosis on 6B365; and neither symptom on Salamouni and M-3. Twelve of the isolates produced necrosis on Glenlea, Katepwa, ND495, 6B365, and Salamouni, and neither symptom on M-3. Necrotic reactions to these isolates on 6B365 (chlorotic or resistant to currently identified 7 races) and Salamouni (resistant to all 7 races), and the resistant reaction on M-3 (resistant to all 7 races) differentiate them from the other seven races. Therefore, we grouped these isolates under a new race and designated this as race 8. To our knowledge, this is the first report on the occurrence of race 8 in P. tritici-repentis. This discovery holds particular significance to breeders and pathologists interested in producing wheat lines with resistance to tan spot. Additionally, we suggest that M-3 be added to the differential set because this line is resistant to all eight identified races. More isolates from Brazil are under investigation to discover the P. tritici-repentis race structure in the country.
References: (1) S. Ali et al. (Abstr.) Phytopathology 92(suppl):S3, 2002. (2) S. E. Strelkov et al. Can. J. Plant Pathol. 24:29, 2002.
