The potato dry rot disease caused by Fusarium spp. seriously reduces potato yield and threatens human health. However, potential biocontrol agents cannot guarantee the stability and activity of biocontrol. Here, 18 synthetic microbial communities of different scales were constructed, and the synthetic microbial communities with the best biocontrol effect on potato dry rot disease were screened through in vitro and in vivo experiments. The results show that the synthetic community composed of Paenibacillus amylolyticus, Pseudomonas putida, Acinetobacter calcoaceticus, Serratia proteamaculans, Actinomycetia bacterium and Bacillus subtilis has the best biocontrol activity. Metabolomics results show that Serratia protoamaculans interacts with other member strains to produce caproic acid and reduce the disease index to 38.01%. Furthermore, the mycelial growth inhibition after treatment with caproic acid was 77.54%, and flow cytometry analysis showed that the living conidia rate after treatment with caproic acid was 11.2%. This study provides potential value for the application of synthetic microbial communities in potatoes, as well as the interaction mechanisms between member strains of synthetic microbial communities.

Potato dry rot, induced by pathogenic Fusarium species, is a prevalent postharvest fungal disease that leads to significant economic losses. This research illustrates the biocontrol efficacy of Bacillus velezensis strain 2-1-9-CJK-2 against potato dry rot. The strain successfully inhibited disease progression, diminished oxidative damage in potato tubers, and augmented the activity of essential defense-related enzymes. It effectively colonized potato tubers and sustained consistent inhibitory activity under diverse environmental challenges. And its cell-free supernatant (CFS) retained consistent inhibitory activity. The crude lipopeptides (CLs) produced by this strain induced hyphal deformation, fragmentation, and cytoplasmic leakage in Fusarium solani. Transmission electron microscopy (TEM) further revealed that CL treatments triggered organelle degradation in the pathogen, with mitochondrial disintegration being particularly prominent. Transcriptomic analysis indicated that CLs upregulated genes linked to mitochondrial autophagy in the pathogen and stimulated plant defense mechanisms, notably the MAPK signaling cascade, in potatoes. The findings were additionally corroborated by qRT-PCR. B. velezensis strain 2-1-9-CJK-2 is a promising biocontrol agent and a great resource for the development of antifungal formulations to enhance sustainable potato production.