The effect and mechanism of Debaryomyces nepalensis and six strains of winter jujube epiphytic bacteria in building a synthetic community to control post-harvest black spot disease of winter jujube.

The study aimed to develop a synthetic microbial community capable of managing postharvest black spot disease in winter jujube. The research revealed that treatment with Debaryomyces nepalensis altered the surface microbial community, reducing the presence of harmful fungi such as Alternaria, Penicillium, Fusarium, and Botrytis, while boosting beneficial bacteria like Pantoea, Bacillus, Staphylococcus, and Pseudomonas, leading to a decreased decay rate in date fruits. A synthetic community was crafted, integrating D. nepalensis with seven other bacterial strains selected for their abundance, compatibility, culturability, and interactions. This community was refined through homo-pore damage experiments and safety assessments to a final formulation consisting of D. nepalensis and six other bacteria: Bacillus subtilis, Bacillus velezensis, Staphylococcus arlettae, Staphylococcus gallinarum, Pseudomonas sp., and Pseudomonas psychrotolerans. Fruit inoculation tests demonstrated that this synthetic community (6 + 1) significantly lowered the incidence and size of black spot lesions compared to single-strain treatments. By the 10th day of storage, the incidence was 69.23 % lower than the control and 52.94 % lower than the group treated solely with D. nepalensis. Mechanistic studies of the synthetic community's antibacterial effects showed that it can produce volatile compounds, proteases, and β-1,3-glucanase to inhibit pathogen growth. Additionally, the community forms a biofilm to compete for nutrients and induce jujube resistance to disease.