Mold and bacteria species associated with spoilage of tubers of sweet potato (ipomoea batatas) in two local government areas of kebbi state, nigeria

Abstract

A comparative investigation of the microbial susceptibility of two varieties of sweet potato (Ipomoea batatas) tubers was conducted across two local government areas (LGAs), Birnin Kebbi and Maiyama, in Kebbi State, Nigeria. The objective was to identify the mold and bacterial species responsible for postharvest spoilage and to determine the variety and locality associated with optimal production and storage potential. Microbial populations were enumerated on Nutrient Agar and Potato Dextrose Agar, and isolates were identified through standard morphological, microscopic, and biochemical procedures. Eight bacterial species, namely Staphylococcus aureus, Salmonella spp., Escherichia coli, Bacillus spp., Pseudomonas spp., Listeria monocytogenes, Klebsiella spp., and Erwinia spp., together with five fungal species, Aspergillus spp., Mucor racemosus, Rhizopus spp., Fusarium oxysporum, and Penicillium spp., were isolated and identified from the two varieties. The yellow skin with white flesh variety collected from Gumben Kure recorded the highest bacterial load (7.2 × 104 cfu/mL), while the lowest bacterial count (3.2 × 104 cfu/mL) was obtained from Gwadangwaji. The highest fungal load (8.0 × 104 cfu/mL) was recorded in the yellow skin with white flesh variety from Gulumbe, and the lowest fungal count (0.8 × 104 cfu/mL) was recorded in the white skin with yellow flesh variety from Mayalo. Pathogenicity tests revealed that all isolated fungi produced varying degrees of tuber rot, with Rhizopus spp. causing the deepest rot (4.2 cm), while Klebsiella spp. produced the deepest bacterial rot (4.0 cm). These findings confirm the microbial basis of sweet potato spoilage in the study areas and underscore the need for improved postharvest handling to safeguard consumer health and reduce economic losses.