Morphological Identification of Potentially Toxin-Producing Molds Contaminating Tomatoes (Solanum lycopersicum L.) in Northern Benin and in-vitro Evaluation of the Antifungal Activity of Lippia multiflora and Ocimum gratissimum Essential Oils

Abstract

Aims: This study aimed to evaluate, under in vitro conditions, the antifungal effectiveness of essential oils extracted from Lippia multiflora (Gambian tea) and Ocimum gratissimum (African basil) against potentially toxin-producing molds associated with tomatoes marketed in northern Benin. Study Design:  A laboratory-based experimental study was conducted to assess fungal contamination of tomatoes and the antifungal activity of two plant essential oils against selected fungal isolates. Methodology: Twenty tomato samples were collected using a non-probability (convenience) sampling method, based on vendor accessibility, from five major markets in Parakou Municipality, Borgou Department, namely GUEMAN, NIMA, ARZÈKÈ, ZONGO, and DÉPOT, with four samples collected from each market. Fungal contamination was assessed using chloramphenicol-supplemented Sabouraud agar. Fungal isolates were identified based on their cultural and morphological characteristics (no molecular confirmation was performed). The antifungal activity of L. multiflora and O. gratissimum essential oils was evaluated at increasing concentrations (50–700 µL) using a direct-contact assay on solid culture medium against the two main fungal isolates, Aspergillus niger and Fusarium solani. Fungicidal or fungistatic effects were determined using the MFC/MIC ratio. Results: The tomato samples showed substantial fungal contamination, although the microbial loads remained within the range established by Quebec standards (10⁴–10⁵ CFU/g). Five major fungal genera were identified: Aspergillus spp. (50%), Penicillium spp. (19%), Fusarium spp. (19%), Cladosporium spp. (6%), and Alternaria spp. (6%). Both essential oils exhibited antifungal activity against A. niger and F. solani. MFC/MIC ratios ≤4 indicated predominantly fungicidal activity. Among the oils tested, L. multiflora essential oil showed the strongest antifungal activity. Overall, fungicidal effects were more pronounced than fungistatic effects and varied according to the concentration applied. Conclusion: These results highlight the considerable potential of these essential oils as natural antifungal agents, offering promising, environmentally safe, and less toxic alternatives to the synthetic fungicides commonly used in Beninese agriculture.