FIRST REPORT OF THE SEXUAL STAGE OF Pyrenophora tritici- repentis IN IRAN

Recently, tan spot disease of wheat caused by Pyrenophora tritici-repentis(Died.) Drechsler has become very important disease in northern parts of Iran and causes severe yield loss. Although the anamorph of the fungus has been reported previously on infected leaves from Mazandaran province (Forotan et al., 1995), but there is no report on mass production of conidia in laboratory and the teleomorph of the fungus in Iran. Infected leaves were collected from wheat fields in Golestan and Mazandaran provinces and were investigated in laboratory and greenhouse conditions. The results showed that after seven days the colonies of the fungus on V8-CaCo3 medium was dark grey color, conidiophores swollen at the base, yellow to brown color, 7-8 μm thick and 100-300 μm long, conidia were yellow, with 5-7 pseudosepta, 14-18 × 100-200 μm and the basal cells were conical. 5-mm plug taken from an active colony margin of a young culture grown on V8-CaCo3 were used to inoculate 2%WA medium containing wheat leaves and these media were kept in special treatment including 12 hours photoperiod of white fluorescent and near UV light at 22 ºC. After two weeks, dark colored pseudothecia with 200-250 μm size, were produced on leaf tissues, Ascospores were oval shape with three transverse and one longitudinal septa, and   16-20 × 40-50 μm size. Based on morphological characters the fungus was identified as Pyrenophora tritici-repentis (Sivanesan, 1987). Pathogenicity test was carried out on susceptible cvs, Bolani and Tajan seedlings at  2-3 leaf stage with suspension of ascospores with concentration of 10⁶ /ml in greenhouse. Inoculated seedlings were kept under black plastic bags for 48 hours under 22 ºC and 16 hours photopriod. Plastic bags were removed, and inoculated seedlings were left under the same condition mentioned. Symptoms of the disease including distinct necrotic and chlorotic lesions were observed after six days on inoculated leaves. The fungus was isolated from the infected leaf tissues. This is the first report of sexual stage of P. tritici-repentis and ability of ascospores to infect wheat from Iran.