Methylobacterium spp. and biological control of phytopathogenic Fusarium spp.

The biocontrol potential of Methylobacterium spp. against key phytopathogenic fungi was evaluated using in vitro antagonism assays and confined germination bioassays. Across 40 Methylobacterium isolates, inhibitory activity was highly variable and strain-dependent. Fusarium graminearum (UAMH 3329) was the most consistently suppressed pathogen; however, only M. thiocyanatum (NBRC 103124) and M. aminovorans (LMG 21752) produced significant inhibition (>30%, p < 0.05) across all three Fusarium species tested. Growth suppression was enhanced on nutrient-minimum agar amended with cell-free bacterial broth, supporting the involvement of diffusible inhibitory factors in fungal growth suppression. However, marked isolate- and substrate-dependent effects suggest that antagonism is contingent on specific bacterium-pathogen combinations. In germination assays, M. organophilum (LMG 6083) conferred protection to soybean (Glycine max) seeds challenged with F. graminearum, improving germination and seedling development in both artificial and soil substrates. Co-inoculated seeds exhibited lower disease severity scores (DSS), fewer necrotic lesions, and reduced fungal colonization during germination and emergence. Collectively, these findings identify candidate Methylobacterium strains with antagonistic activity against Fusarium spp. and provide a foundation for future characterization of their effectors relevant to integrated crop protection.