Mycological Cross-Infection Potentials and Susceptibility Indices Associated with Watermelon (Citrullus lanatus) Fruits Isolates in Owerri, Nigeria.

The mycological cross-infection potential, virulence, and susceptibility indices of watermelon fruits (Citrullus lanatus) isolates in Owerri, Nigeria, were evaluated using standard microbiology methods, which include enumeration, cross-infection/ pathogenicity, and susceptibility tests. One hundred and fifty watermelon samples were randomly selected. The mean fungal levels ranged from 0.03 × 10³ to 1.46 × 10³ CFU/g and were within safe thresholds (≤10⁴ CFU/g) for ready-to-consume fruits. The four fungal genera identified were: Aspergillus, Penicillium, Rhizopus, and Mucor. Cross-infection tests showed that all the isolates could cause spoilage with the highest virulence index (VI=37.04) by Aspergillus, within 2 days of latent period, and the longest lesion length of 3.76 cm on fresh cucumber fruits (Cucumis sativus). The antifungal susceptibility test showed varying degrees of responsiveness. Aspergillus was highly sensitive to Amphotericin B and Nystatin, and intermediate to Ketoconazole. Conversely, Penicillium and Mucor were highly resistant to Griseofulvin, Clotrimazole, Fluconazole, and Ketoconazole. Amphotericin B and Nystatin are the preferred drugs for treatment, offering the broadest spectrum of activity and 75% efficacy among isolates. The findings highlight significant concerns regarding post-harvest fungal infestation, cross-infection risks, and the emergence of antifungal resistance.