Isolation and Identification of Fungal Species Associated with Post-harvest Spoilage of Onions (Allium cepa) in the Kafin Hausa Market, Jigawa State, Nigeria

Post-harvest fungal spoilage of onions contributes to significant global economic and food security losses, with up to 30% of harvested bulbs lost annually in developing regions. A study was conducted to isolate fungal species responsible for the spoilage of onions sold at Kafin Hausa Market, Jigawa State, Nigeria. The collected onion samples were cut into pieces of about 5 mm using a sterile razor blade, cultured on potato dextrose agar (PDA), and incubated at room temperature for 5–7 days. Fungal isolates were sub-cultured and purified onto PDA plates. Morphological identification techniques (macro- and micromorphological features) were assessed via lactophenol cotton blue staining and taxonomic keys. A total of 37 fungal isolates were obtained from 12 samples collected across 3 stations (A, B, and C). Result from the determination of frequency of occurrence show that, fungus with the highest frequency was Aspergillus niger (40.54%), followed by Alternaria alternata (16.22%), Rhizopus stolonifer (13.51%), Fusarium oxysporum (10.81%), Aspergillus flavus (8.11%), Penicillium digitatum (8.11%), and Aspergillus fumigatus (2.70%) with frequencies differing significantly across sampling stations (p < 0.05). This finding provides the first empirical documentation of onion spoilage fungi in the Kafin Hausa region of Jigawa state, Nigeria, identifying A. niger as the primary contaminant, and suggests the urgency of improved post-harvest practices (e.g., temperature-controlled storage) to mitigate losses.