Characteristic symptoms of melon diseases caused by fungi in south western Nigeria

Abstract

In a survey of farmers’ fields across four states of south western Nigeria, major diseases of egusi melon were evaluated and symptoms described. Pathogenicity tests of foliage and fruits were conducted in the laboratory and causal pathogens identified. Powdery mildew (Erysiphe cucurbitarum) appeared as round whitish spots on the lower surface which increased in size and later appeared as whitish talcum on the upper surface. Downy mildew (Peronospora cucurbitarum) appeared on the upper surface as small and pale green to yellow angular spot which became chlorotic and shriveled. Alternaria leaf spot (Alternaria cucumerina) appeared as small circular water soaked areas which turned dark brown to black; and Cercospora leaf spot (Cercospora citrullina) appeared as circular spot with white to tan centers having dark margins. Foliar spots which began as small yellowish water- soaked areas on the veins that later turned circular, dried up, broke and became shattered were symptoms observed for the Anthracnose disease (Colletotrichum lagenarium). Fruit anthracnose started as small, circular, black, sunken canker with raised margin. Leaf blight, stem blight and fruit rot (Didymella bryoaniae) disease symptoms were observed on leaves, stems and fruits respectively. Leaf symptoms began as light brown, irregular spots surrounded by yellow borders that developed from the tip of the leaves and gradually progressed backwards. Brown lesions were observed on the stem which split open and turned dark. Lesions observed on fruits appeared as small, almost circular water- soaked areas which enlarged, resulting in dark, firm and leathery depressed areas. Symptoms of vine wilt were observed as elongated brown lesions which developed on stems near the crown and extended as long, narrow, brown streaks causing stem to completely wilt. Wet rot of flower and fruit (Choanephora cucurbitarum) appeared as characteristic fungus growth resembling numerous pins stuck in a pin-cushion on the infected surface. The study will help to bridge the gap of information on the characteristic symptoms and causal pathogens of melon diseases in south western Nigeria Key words: “Egusi” melon, south western, field diseases, symptoms.