STUDIES ON THE FALSE SMUT OF RICE, ORYZA SATIVA L., INDUCED BY USTILAGINOIDEA VIRENS (CKE.) TAK

STUDIES ON THE FALSE SMUT OF RICE, ORYZA SATIVA L., INDUCED BY USTILAGINOIDEA VIRENS (CKE.) TAK

Abstract:

The incidence and severity of false smut of rice incited by (Ustilaainoidea virens (ke.) Tak.) in the major rice producing areas of Edo State was investigated in 1992. Although the disease was present in all the areas surveyed, it was most prevalent and severe in Ovbiowun-Emai, and Uokha, both in Owan East of Edo State. The mean incidence and severity of false smut in the area between mid-August and mid-September were 28.5% and 13.9% respectively compared to 8.9% and 3.4% for late-September to mid-October. A pathogenicity trial conducted at the University of Benin, Benin City in 1993 revealed that false smut was reproduced only when rice panicles were sprayed with either chlamydospores or conidia suspension at ‘heading’ stage. Inoculation at ‘booting’ or ‘milk-grain’ stage respectively did not cause any infection. Field trials were conducted at Ovbiomun-Emai, in 1993 and 1994 to determine the effect of sowing date, plant density, varietal resistance, and fungicidal sprays on the incidence and severity of the disease. Rice sown with the early rains, between early-April and early-May, were virtually free from false smut infection. On the other hand, mid-season sowing, between mid-May and early-June, recorded the highest incidence and severity of false smut. There were no significant differences (P = 0.05) among the severities of false smut at three spacing levels (0.2 x 0.2m, 0.4 x 0.4m and 0.4 x 0.8m) tried. Of the seven rice varieties screened against false smut under field conditions, at two sites, ITA 316, Ex-china and IRAT 170 were the most resistant. The other four varieties were susceptible. Delsene M, Benlate, Tecto, and Cupravit, at the three concentrations tried in-vitro, completely inhibited mycelial growth of U. virens; while Dithane M-45 and Rovral reduced mycelial growth by 62.2% and 47.8% respectively. Four sprays each of the six fungicides at an interval of 7-days, starting at the sighting of the first ‘boot’, were found to reduce incidence and severity of the disease in the field. However, the best result was obtained by spraying with cupravit. This resulted in 75.9% reduction in disease incidence and significantly increased grain yield by 43.2% when compared with the control. Dithane M- 45 sprays also resulted in 47.0% disease reduction, but did not increase grain yield significantly. Delsene M sprays apparently gave a 100% disease control, but was highly phytotoxic to the rice plants at the recommended rate.

STUDIES ON THE FALSE SMUT OF RICE, ORYZA SATIVA L., INDUCED BY USTILAGINOIDEA VIRENS (CKE.) TAK

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