A simplified synthetic community from the healthy watermelon rhizosphere effectively mitigates Fusarium wilt

Watermelon production is threatened by Fusarium oxysporum f. sp. niveum (Fon) in continuous cropping systems. Plant-recruited protective microbes can be assembled into synthetic communities to combat infections caused by Fon. The objective of this project was to assemble a simplified synthetic community for use in controlling Fusarium wilt in watermelon.

The Shannon diversity of the bacterial community in the roots and rhizosphere of healthy watermelon plants was significantly higher than that of diseased plants. Under Fon challenge, healthy watermelon plants recruited certain beneficial bacteria taxa, such as Lysobacter, Microbacterium, Nocardioides and Sphingobium to the rhizosphere and roots. We identified the top ten bacterial genera enriched in the rhizosphere of healthy watermelon plants and utilized them to construct a disease-resistant synthetic community (SynCom I). After the joint selection of plants and pathogens, the synthetic community (SynCom I) containing ten bacteria was further simplified into a five-species community comprising Bacillus methylotrophicus J4, Agromyces mediolanus L1P43F5, Microbacterium maritypicum L2P04F12, Sphingobium mellinum L2P11G4 and Chryseobacterium lactis L1P41C5. The simplified synthetic community demonstrated a control efficacy of 99.6%, and the five-species members presented a cross-feeding interaction model. Removal of any one of B. methylotrophicus J4, Chryseobacterium lactis L1P41C5 and Sphingobium mellinum L2P11G4 led to an increase in the incidence rate compared with the synthetic community. In addition, B. methylotrophicus J4 and Chryseobacterium lactis L1P41C5 significantly promoted plant growth.

Our findings indicate that specific bacterial taxa enriched in the rhizosphere of healthy plants are correlated with enhanced disease resistance. Consequently, the construction and simplification of synthetic communities observed in this study may represent a strategy utilized by plants to mitigate the impact of Fusarium oxysporum f. sp. niveum. © 2025 Society of Chemical Industry.