Bacillus megaterium controls melon Fusarium wilt disease through its effects on keystone soil taxa

Aims Melon Fusarium wilt, caused by Fusarium. oxysporum f. sp. melonis, is a severe soil-borne disease that reduces melon yield. Biological control approaches have been shown to be effective for the control of melon Fusarium wilt and could contribute to the sustainable development of the melon industry. Bacillus megaterium (BM) is a biocontrol strain that has been shown to promote plant growth and control plant diseases. However, few studies have examined the mechanism by which BM controls melon wilt disease. Methods In this study, we investigated the effect of BM on the growth of melon plants, as well as on soil microbial communities, the soil microbial co-occurrence network, and keystone soil taxa. Results Using a pot experiment, we showed that the incidence of melon Fusarium wilt decreased from 68.33% (CK, inoculated with sterile water) to 26.67% (inoculated with BM), and the control efficiency was 60.00%. In the field experiment, the incidence of melon Fusarium wilt was reduced from 5.56% (naturally occurring) to 1.67% after BM treatment, and the control efficiency was 69.44%. BM treatment also promoted the growth of melon plants and increased the yield of melon to 20.35%. The abundance of potentially beneficial microbes (e.g., Flavobacterium, Nocardioides, Streptomyces, and Chaetomium) and potentially pathogenic microbes (e.g., Alternaria, Aspergillus, Mortierella, and Plectosphaerella) was higher and lower in the BM treatment than in the CK, respectively. Co-occurrence network complexity was higher in the BM treatment than in the CK, and the keystone taxa OTU2869 (Pseudomonas), OTU3763 (Sphingobacterium), and OTU2440 (Streptomyces) play key roles in the BM treatment than in the CK. Conclusions The results of our study indicated that BM could be an effective biocontrol agent for the control of Fusarium wilt that could increase melon yield. BM also altered the composition of keystone soil taxa, indicating that it could alter the composition of the soil microbial community, which could promote plant growth and decrease the incidence of melon Fusarium wilt.