EFFECT OF BROWN LEAF SPOT DISEASE ON THE GROWTH AND YIELD OF SWEET POTATO

Abstract

Polybagged sweet potato plants were inoculated with conidia of Cercospora batatae scraped from sweet potato leaves infected with brown leaf spot. The completely randomized design was followed in laying out the experiment. Leaves inoculated at different ages showed varying responses to infection with significant differences in the number and size of lesions and percentage of defoliation. Leaves inoculated at 15-21 days old were found most susceptible to the disease. Initial symptom of the disease was first observed as light green lesions approximately 0.5 mm in diameter 2 weeks after inoculation. The lesions increased gradually until they reached 3 to 4.2 mm diameter 32 days after inoculation. Coalition of lesions was observed at this stage followed by subsequent defoliation. Inoculated plants showed decrease in yield resulting from the adverse effects on yield components. The two trials yielded 9.57%, 5.05% and 26.23% reduction in weight of tubers, roots and tops, respectively. The number of tubers also decreased in inoculated plants. Analysis of variance of weight of tops showed significant difference from the uninoculated ones while the other parameters were not significantly different.