Antimicrobial Potential of Endophytic Fungi from Capsicum annuum and Vigna Unguiculata Against Xanthomonas campestris and Fusarium oxysporum

Abstract

This study investigated the isolation and characterization of endophytic fungi from Capsicum annuum and Vigna unguiculata, and evaluated their biocontrol potential against Xanthomonas campestris and Fusarium oxysporum. Endophytes were isolated from surface-sterilized plant tissues collected in Katsina State, Nigeria. Four fungi Alternaria sp., Aspergillus niger, Penicillium sp., and Rhizopus stolonifer—were identified based on morphological characteristics. Antimicrobial activity of fungal culture filtrates was assessed in vitro using the agar well diffusion method at concentrations ranging from 25 to 100 µg/mL. Secondary metabolites of active isolates were analyzed using Liquid Chromatography–Mass Spectrometry (LC-MS). Results showed a dose-dependent inhibition by Penicillium sp. and A. niger, while Alternaria sp. and R. stolonifer exhibited no activity. Penicillium sp. demonstrated the highest efficacy, with inhibition zones of 24.5 ± 2.2 mm against X. campestris and 16.6 ± 0.3 mm against F. oxysporum at 100 µg/mL. Aspergillus niger showed moderate inhibition with zones of 17.1 ± 1.5 mm and 11.3 ± 0.22 mm, respectively. LC-MS profiling revealed the production of penicillin G and griseofulvin by Penicillium sp., and 2-phenylethanol by A. niger. However, both fungi also produced mycotoxins such as ochratoxin A, patulin, and gliotoxin. The study highlights the strong biocontrol potential of Penicillium sp. and A. niger, alongside significant biosafety concerns, emphasizing the need for non-toxigenic strains for sustainable agricultural application in Nigeria.