RACE IDENTIFICATION OF PYRENOPHORA TRITICI-REPENTIS IN IRAN

Tan spot is a destructive foliar disease of wheat caused by the fungal pathogen Pyrenophora tritici-repentis. Recently, tan spot has become a serious problem in the northern parts of Iran, where it causes severe yield losses. The objective of this study was to identify the physiological races of P. tritici-repentis in Iran, and to test isolates from this country for the presence of the toxin-encoding genes ToxA and ToxB. In total, 184 isolates were collected from two provinces, Golestan and Mazandaran, near the Caspian Sea. The virulence of 48 of these isolates was evaluated on four differential wheat genotypes. Race 1 was predominant and represented 90% of the tested isolates, while the remaining 10% were classified as race 2. No other races were identified. ToxA-and ToxB-specific primers were used in a PCR-based analysis to detect the presence of these genes in the Iranian isolates. The ToxA gene was amplified from all of the isolates evaluated, while no amplicon was obtained from any of the isolates with the ToxB-specific primers. The presence of ToxA and absence of ToxB is consistent with the race designation of the isolates. The ToxA sequence from 10 isolates selected, based on geographical origin, was found to be identical, and also shared 100% identity with other ToxA sequences from P. tritici-repentis in GenBank. This is the first study of the race structure of P. tritici-repentis in Iran.