Identification of the major foliar fungal disease of colocasia esculenta (l.) schott. and its management in the Kumasi Metropolis.

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August, 2010.
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Colocasia esculenta (L.) Schott. is a major delicacy in southern Ghana with high carbohydrate and protein contents. Recent decline in the production of C. esculenta in swampy fields has resulted from leaf blight disease, making the disease a threat to food security. A survey was conducted to assess the disease problem and also assess farmers’ knowledge. The disease occurred on every C. esculenta field surveyed and disease incidence was between 80-90%. Five potted plants were inoculated with each fungal isolate obtained from farmers’ fields and observed for symptom expression. Symptoms appeared as small dark-brown lesions which extended rapidly until death of leaves. The pathogenicity test showed that Curvularia sp. was responsible for the leaf blight disease. A study of disease progress on tagged leaves on swampy C. esculenta fields indicated that leaf blight appeared on leaves just as they unfurl and spread rapidly, debasing the leaf within 18 to 21 days. In a field trial, Topsin M 70 WP (Thiophanate methyl), Sundomil 72 WP (Metalaxyl 8% and Mancozeb 64%) both at 45 g/15l and water (control) sprayed at two-week intervals were evaluated against leaf blight disease incidence, severity, the disease progress and corm yield. The effect of the fungicides on leaf area, area of leaf infected by the disease, lesions per plant and number of leaves that died as a result of the disease, were also investigated. Fungicides-treated Colocasia plants showed significantly reduced disease incidence, disease severity and disease progress that resulted in increased corm yield. There were no differences between fungicides-treated Colocasia plants. There was a negative correlation between area of leaves infected, lesions per plant, number of leaves infected and the corm yield. The results from the field trial showed that leaf blight disease could be effectively managed with fungicides in swampy fields.
A thesis submitted to the school of Research and Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfilment of the requirement for the award of the degree, Master of Science in Plant Pathology.