Clement G. Afolabi1* and Sunday O. Adigbo2
Rice blast caused by the fungus Pyricularia grisea, is one of the limiting factors in rice production causing severe losses under favourable environmental conditions. The effects of nitrogen applications on leaf blast development and yield of rice were studied under sawah system of production. WITA-4 and Jasmine rice varieties were planted and four levels (0, 30, 60 and 90 kg ha-1) of urea fertilizer were imposed. Nitrogen and rice varieties treatments were arranged in a split plot design with N levels as main plots and varieties as subplots, with three replications. The results obtained indicate that Jasmine variety was not infected by the blast pathogen whereas WITA-4 variety was susceptible to the disease. Disease incidence was generally high on 0 and 90 kg ha-1 but there was no significant difference among treatments. However, there was a significant difference (P=0.0001) between the N treatments for final disease severity score and the total lesion area, with 90 kg ha having the highest severity score and total lesion area. Significant differences between nitrogen treatment (P=0.001), varieties (P=0.01) and the nitrogen treatment x cultivar interactions (P=0.05) with respect to grain yield were observed. In terms of yield, Jasmine variety had 5.4 tons/ha on 90 kg ha -1 N treatment but the effect of the blast was pronounced on WITA-4 variety with 4.7 tons/ha. Rice cultivation under sawah system does not preclude rice from blast infection; hence, an appropriate management system must be incorporated to ensure bumper harvest.
Keywords: Rice, Leaf Blast, Nitrogen, Sawah, Yield, Nigeria