Race structure of Pyrenophora tritici-repentis prevalent on wheat in Argentina

MORENO M.V., STENGLEIN S.A. & PERELLÓ A.E.

Simposio; 4th International Symposium on Plant Protection and Plant Health in Europe; 2011

Tan spot caused by Pyrenophora tritici-repentis is a common disease of wheat worldwide. It has increased in the whole of the South Cone region in the last few years. The race structure and Tox genes of 65 monosporic isolates of P. tritici-repentis collected from wheat at different regions of Argentina were analyzed. Virulence tests were conducted on the wheat seat cultivars and lines Glenlea, Salomouni, Katepwa, M-3, 6B365 and 6B662 under chamber plant conditions. Based on the reaction types on standard differentials,  33 P. tritici- repentis isolates were grouped into seven known races. One isolate was classified as race 1, four isolates as race 2 and one as race 3, 11 isolates as race 4, one as race 5, one as race 6 and 13 isolates were classified as race 8. The restof the isolates could not be classified into races. The presence/absence of the Tox A, Tox B and tox b genes using PCR specific-primers revealed that 57 isolates amplified the fragment that correspond to the Tox A gene, one isolate to the Tox A and Tox B, and the remaining seven isolates lacked these genes. Low associations were found between grouping the isolates based on phenotypic races and their toxin production genes. Although some isolates amplified for the Tox A gene, they did not express it through the production of necrosis. On the other hand, most of the isolates produced chlorosis on different cultivars but only one of them amplified for the Tox B gene. These results indicates a diverse races population of P. tritici-repentis on wheat in Argentina, suggesting a novel toxin(s) involved from isolates that induce necrotic-chlorotic tan spot symptoms.