ISOLATION OF FUNGI ASSOCIATED WITH ONION SPOILAGE IN MARKET IN BENIN CITY

ABSTRACT

This study was carried out to investigate fungal species associated with onion bulb spoilage. Twenty seven samples of onion bulbs were purchased from three different markets in Oredo local Government Area, Benin City, Edo State. The samples were transported to the laboratory for microbiological analysis using pour plate isolation and plant plate isolation method. Serial dilutions up to 10⁶ were performed for each sample and aliquot of 1ml was plated out using potato dextrose agar and malt yeast agar. Chloramphenicol antibiotic was added to the aliquot in the plate to discourage bacterial growth, before molten agar was poured. Plates were incubated at room temperature for 3-5 days. Colonies were counted and pure culture was obtained by pour plate method. Culturing was done every week for one month, to monitor the degree of fungal spoilage of the onion bulb. Isolated fungi were identified based on their cultural and microscopic characteristics. Results of fungal count from potato dextrose agar revealed increase in fungal counts in samples from Oba market with counts ranging from 4.0 x 10⁶cfu/ml in week one to 6.1 x 10⁶cfu/ml in week three. In samples from New Benin and the third market, the fungal counts increased from week one to week four (3.9 x 10⁶cfu/ml to 7.3 x 10⁶cfu/ml ) and 3.7 x 10⁶cfu/ml to 5.7 x 10⁶cfu/ml (for third market).In malt yeast agar, counts ranged from 1.9 x10⁶cfu/ml to 6.3 x10⁶cfu/ml for Oba market; 4.1 x10⁶cfu/ml to 5.9 x10⁶cfu/ml for New Benin and 2.0 x10⁶cfu/ml to 6.8 x10⁶cfu/ml for third market respectively. Fungal species isolated from onion bulb were Penicilliun species, Fusarium species, Aspergillus species, Rhizopus species, Alternaria species and Saccharomyces species were found to be the least occurring fungal isolate with percentage distribution of 3.7% while Aspergillus species was the most occurring isolate with percentage distribution of 59.3%. Penicillium, Fusarium and Rhizopus species had percentage distribution of 7.4% while Saccharomyces species had a percentage distribution of 15.0%. This work has shown that fungal isolates can aid spoilage of onion bulb. Therefore, appropriate storage method should be used to prevent onion spoilage.