Biocontrol Potential of Rhizosphere Bacteria Against Fusarium Root Rot in Cowpea: Suppression of Mycelial Growth and Conidial Germination.

The cultivation of cowpea (Vigna unguiculata), a vital vegetable crop, faces significant threats from Fusarium spp.-induced root rot. In this study, three fungal pathogens (Fusarium falciforme HKFf, Fusarium incarnatum HKFi, and Fusarium oxysporum HKFo) were isolated from symptomatic cowpea plants, and we screened 90 rhizobacteria from healthy rhizospheres using six culture media. Among these pathogens, Priestia megaterium TSA-10E showed a notable suppression of F. oxysporum HKFo (63.21%), F. incarnatum HKFi (55.16%), and F. falciforme HKFf (50.93%). In addition, Bacillus cereus KB-6 inhibited the mycelial growth of F. incarnatum HKFi and F. oxysporum HKFo by 42.39% and 47.93%, respectively. Critically, cell-free filtrates from P. megaterium TSA-10E and B. cereus KB-6 cultures reduced conidial germination in F. oxysporum HKFo and F. incarnatum HKFi, highlighting their role in disrupting the early infection stages. In greenhouse trials, TSA-10E and KB-6 reduced disease severity by 48.7% and 40.4%, respectively, with treated plants maintaining healthy growth while untreated controls succumbed to wilting. Broad-spectrum assays revealed that B. subtilis TSA-6E and P. megaterium TSA-10E were potent antagonists against both economic and grain crop pathogens. These findings underscore the potential of rhizobacteria as sustainable biocontrol agents for managing root rot disease caused by Fusarium spp. in cowpea cultivation.