A simplified synthetic community for controlling Fusarium wilt in watermelon

Abstract:

[Background] Fusarium wilt in watermelon, a serious soil-borne disease caused by Fusarium oxysporum f. sp. niveum (Fon), reduces watermelon quality and yield worldwide. [Objective] To determine whether a simple synthetic bacterial community has similar effects as a complex synthetic bacterial community, we assembled a simplified synthetic bacterial community for controlling Fusarium wilt in watermelon based on the screening of strains with the plant and pathogen. [Methods] The 16S rRNA gene sequencing and real time fluorescence quantitative PCR were employed to analyze the effects of SynCom Q on the abundance of bacteria and Fon in watermelon roots and rhizosphere. Based on the results of 16S rRNA gene sequencing, the bacteria colonizing the roots and rhizosphere were identified, and a simplified synthetic community SynCom R was constructed. Pot experiments and antagonistic experiments were carried out to evaluate the control effect of SynCom R on Fusarium wilt in watermelon and the antagonistic activity of SynCom R against Fon, respectively. The physiological and biochemical characteristics of four bacterial species in SynCom R were evaluated by plate qualitative tests. The cross-feeding assay was employed to examine the effects of the four bacterial species in SynCom R on the growth of each other. [Results] The application of SynCom Q altered the structures of bacterial communities in watermelon roots and rhizosphere, and Chryseobacterium, Sphingomonas, and Rhizobium were enriched in watermelon roots and rhizosphere. SynCom Q increased the abundance of bacteria in the roots and rhizosphere and decreased the abundance of Fon in the rhizosphere. The joint screening with the plant and pathogen showed that Enterobacter ludwigii LSQ1, Acinetobacter pittii LSQ3, Bacillus velezensis LSQ19, and Bacillus velezensis WB could colonize the roots and rhizosphere of watermelon, and thus SynCom R consisting of E. ludwigii LSQ1, A. pittii LSQ3, B. velezensis LSQ19, and B. velezensis WB was assembled. Compared with single bacterial species and SynCom Q, SynCom R inhibited the growth of Fon. Pot experiments showed that SynCom R decreased the incidence of watermelon Fusarium wilt, with higher disease control effect higher than other bacterial communities. E. ludwigii LSQ1, A. pittii LSQ3, B. velezensis LSQ19, and B. velezensis WB were capable of producing extracellular enzymes and had other physiological functions. The cross-feeding assay showed that the metabolites of B. velezensis LSQ19 and B. velezensis WB promoted the growth of each other, while there was no significant inhibitory or promoting effect between other bacteria. [Conclusion] SynCom R can effectively control Fusarium wilt in watermelon and demonstrates a broad application prospect.

Key words:community simplification;Fusarium wilt in watermelon;biocontrol;antifungal activity