Isolation and Identification of Fusarium oxysporum Causing Cowpea Fusarium Wilt in Hainan and In Vitro Screening of Antagonistic Bacteria

Abstract

Cowpea (Vigna unguiculata subsp. sesquipedalis, also known as yardlong bean) is an important winter horticultural crop in Hainan, and Fusarium wilt seriously threatens its yield and quality. To clarify the pathogen and screen antagonistic bacteria, surveys were conducted in 14 fields across Hainan’s major cowpea-growing areas. The causal agent was isolated, tested for pathogenicity, and identified using morphological and multigene molecular methods. Meanwhile, rhizosphere and endophytic bacteria from healthy plants were screened by dual culture, and candidate strains were phylogenetically analyzed using whole-genome sequencing (285 orthologous single-copy genes). Fusarium wilt occurred in all 14 fields (mean incidence 15.35%, range 3.20–76.40%). Of 44 fungal isolates, six were highly pathogenic and identified as Fusarium oxysporum. Twenty-two bacterial strains showed stable antagonism against F. oxysporum, with inhibition rates ranging from 42.62% to 68.47%. Phylogenetic analysis based on whole-genome sequences identified 15 Bacillus strains to the species level (12 B. velezensis, 2 B. subtilis, 1 B. tropicus), while the remaining seven strains belonged to Lysinibacillus (1), Pantoea (1), Klebsiella (1), Serratia (2), and Pseudomonas (2). Draft genome sequences of all 22 strains were obtained. This study provides a collection of biocontrol bacterial resources and genomic information for managing cowpea Fusarium wilt.