Mycoflora of sun-dried sweet potato (Ipomoea batatas L.) slices in Benin City, Nigeria

A study was carried out to isolate and quantify the fungi present in sun-dried sweet potato slices in Benin City, Nigeria. Potato tubers were peeled, washed, sliced and sun-dried for 30 days. Oven-dried slices served as control. Meteorological data were obtained for the period of study. Fungal colonies on slices were counted with the aid of a hand lens and the average number of colonies calculated. The relative density of each fungus was determined by plating on potato dextrose agar and incubating for 7 days at +/- 28 degrees C. Fungi were isolated and identified and colony forming unit (cfu) determined. Results revealed 12 fungal species, whereas the control had no fungal growth. Isolated fungi were Botryodiplodia theobromae, Rhizopus stolonifer, Mucor mucedo, Aspergillus niger, A. fumigatus, A. flavus and Penicillium digitatum in May (relative density = 5.5-29.4%). A. ochraceus, Curvularia sp. and Neurospora sitophila were isolated in June in addition to the above fungi (relative density = 2.1-23.2%). Eight fungi were isolated in July (relative density = 2.6-26.8%). The cfu ranged from 2.8 x 10(6)-11.6 x 10(6) in May, 1.9 x 10(6)-9.1 x 10(6) in June to 4.1 x 10(6)-11.3 x 10(6) in July. Other means of drying such as tunnel dryers (operated at 60-70 degrees C) and drum-drying are recommended.