Evaluation of the Efficacy of Allium sativum (Garlic) and Syzygium aromaticum (Clove) Against Postharvest Fungal Rot of Ipomoea batatas (Sweet Potato).

Abstract

Postharvest fungal rot is a severe barrier to sweet potato (Ipomoea batatas L.) production in Nigeria, with diseases such as Rhizopus stolonifer, Fusarium spp., Aspergillus niger, and Penicillium spp. Accounting for 20-40% of storage losses. The extensive use of synthetic fungicides has prompted concerns about their environmental impact, human health, and the development of pathogen resistance, emphasizing the need for sustainable botanical alternatives. This study assessed the antifungal activity of ethanolic garlic (Allium sativum) extract and clove (Syzygium aromaticum) bud preparations in the treatment of sweet potato postharvest fungal rot. A total of 147 healthy tubers were divided into seven treatments in a perfectly randomized design with three replications. The treatments included garlic extract at doses of 75%, 50%, and 25%, clove powder, entire clove buds, mancozeb as a positive control, and an untreated control. Treated tubers were maintained at room temperature for six weeks, with weekly checks on weight loss, disease incidence, and disease severity index (DSI). Standard phytochemical screening was also performed on the plant materials. Phytochemical research revealed the presence of alkaloids, flavonoids, phenols, and steroids in garlic extract, whereas clove preparations also contained tannins and saponins. Clove powder resulted in the lowest weight reduction (17.7 ± 1.39%) compared to the untreated control (27.3 ± 0.81%). Both clove powder and 25% garlic extract significantly reduced illness incidence and severity, with efficacy comparable to mancozeb; however, treatment differences were not statistically significant (p > 0.05). The data show that clove powder and low-concentration garlic extract are effective botanical agents for preventing postharvest fungal degradation and preserving sweet potato quality. Their comparable performance to synthetic fungicides, combined with their affordability and environmental compatibility, suggests that these botanicals could serve as long-term alternatives for postharvest disease management, resulting in lower storage losses, less chemical dependence, and improved food security.