Fungi are the most significant and predominant pathogens infecting a wide range of host plants and causing economically important losses to crop produce in transit and storage. In this study, fungi associated with postharvest rot of onion bulbs and their effects on the proximate composition was investigated. Diseased onion bulbs were obtained from three markets around Lagos State University, Ojo Nigeria. Potato Dextrose Agar (PDA) and Malt Extract Agar (MEA) were used for isolation. Pathogenicity test was conducted to determine the causal organism(s) from isolated fungi. Proximate analysis was carried out on infected onion bulbs to ascertain the effects of fungi on the moisture, ash, crude fat, protein and ascorbic acid contents. The fungi isolated from the bulbs were Aspergillus flavus, Aspergillus niger, Rhizopus sp. and Penicillium sp. Pathogenicity tests showed that all isolated fungi induced disease symptoms when inoculated on healthy onion bulbs. The fungi were found to cause an increase in the moisture content of the bulbs and a general reduction in the nutritional composition of the bulbs.

Keywords : Onion Bulbs, Postharvest Rot, Fungal Pathogens, Nutritional Composition.