Fungi Associated with Tuber Spoilage and Their Pathogenicity in Makurdi, Benue State Nigeria

Background: Postharvest fungal spoilage of yam and sweet potato remains a major challenge in Nigeria and Africa at large. It affects food security, storage quality, and marketability of tuber crops. Objective: This study aimed to isolate, identify, and assess the pathogenicity potential of fungi associated with yam and sweet potato spoilage in Makurdi, Benue State, Nigeria. Methodology: Yam and sweet potatoes were obtained from farmers in Makurdi, Benue State. The yams were stored for five months and observed for rot. The experiment was a 2x4 factorial in a completely randomised design with tuber type (Yam and Sweet potato) and variety (White Yam, Water Yam, Cream-fleshed Sweet Potato, Orange-fleshed Sweet Potato). It was replicated three times, with a total of 10 tubers per lot. Thus, the total number of tubers was 240, consisting of 120 yams and 120 sweet potatoes. Fungal isolation was carried out at the end of the experiment. Identification of fungal isolates was conducted using macroscopic, microscopic, and molecular methods. The molecular characterisation involved DNA extraction, PCR amplification using ITS-1 and ITS-4 primers, agarose gel electrophoresis, sequencing, and BLAST analysis using the NCBI database. Pathogenicity testing was carried out on healthy yam and sweet potato tubers following Koch’s postulates. Data obtained were analysed using analysis of variance (ANOVA) and means were separated using Fisher’s least significant difference (FLSD) at 5% probability level. Results: Three fungal species, namely Aspergillus fumigatus, Lasiodiplodia theobromae, and Rhizopus stolonifer were isolated from the tubers. Sweet potato tubers yielded Aspergillus fumigatus, and Rhizopus stolonifer only, while yam tubers yielded all three identified species. Molecular analysis showed high sequence similarity ranging from 96.04% to 98.99%. Pathogenicity tests also confirmed that all isolates were capable of inducing rot in healthy yam tubers. Rhizopus stolonifer caused the highest rot with a severity of 11.70 cm², followed by Aspergillus fumigatus (9.42 cm²) and Lasiodiplodia theobromae (7.82 cm²). The study further revealed that yam tubers harboured a greater diversity of fungal pathogens than sweet potato tubers. Conclusion: Spoilage of yam and sweet potato in Makurdi is caused by fungal pathogens. The high pathogenicity of fungi such as Aspergillus fumigatus raises a public health concern due to the danger it poses to human health. It is therefore recommended that improved storage practices and environmentally friendly postharvest management strategies be adopted to reduce fungal spoilage and preserve the quality of tuber crops during storage.