Biocontrol of watermelon Fusarium wilt caused by Fusarium oxysporum f. sp. niveum with Corallococcus sp. EGB.

Watermelon Fusarium wilt is a severe soil-borne disease that threatens continuous watermelon production. Effective disease control depends on the differentiation of pathogen races, the accumulation of soil-borne inoculum, and disturbances in the soil bacterial community caused by continuous cropping. In this study, a pathogenic fungus was isolated from diseased watermelon plants in a continuously cropped field in Dongtai, Jiangsu Province, China. Morphological characterization, multigene phylogenetic analysis, and pathogenicity assays revealed that the pathogenic isolate belongs to Fusarium oxysporum f. sp. niveum (FON). The biocontrol efficacy of the predatory myxobacteria Corallococcus sp. EGB against FON was also evaluated under field conditions in Dongtai. Strain EGB maintained high target gene copy numbers in soil under consecutive cropping, which in turn reduced the FON target gene copy numbers and thereby lowered the incidence of fusarium wilt. Additionally, EGB application alters the composition of the root-zone soil bacterial community, shifts dominant taxa, and changes diversity patterns in the field experiments. These results indicate that EGB effectively suppresses watermelon Fusarium wilt caused by FON under field conditions, supporting the potential of EGB as a sustainable strategy for managing watermelon Fusarium wilt.