Objectives Bacterial wilt is a prevalent bacterial disease severely affecting tobacco production. We prepared a composite bioorganic fertilizer using highly resistant antagonistic bacteria exhibiting chemotaxis. The rhizosphere colonization and disease resistance mechanisms were investigated.

Methods Five strains of antagonistic bacteria with high resistance to bacterial wilt and chemotaxis were isolated and identified by our team. They were designated as Y364 (Pseudomonas nicosulfuronedens), Y832 (Pseudomonas delhiensis), Y878 (Bacillus altitudinis), Y391 (Pseudomonas nitroreducens), and Y835 (Bacillus safensis). Preliminary studies confirmed no mutual inhibition among these five antagonistic strains, enabling their formulation into a composite microbial agent. The employed tobacco bacterial wilt pathogen was Ralstonia solanacearum (GenBank accession number KC888020). Four locally common organic fertilizers, vermicompost, vinasse, cow manure and rape seed cake, were mixed at varying mass ratios to be used as microbial nutrient carriers. The test bacterial strains were inoculated into each carrier and fermented for a total of 7 days. The prepared microbial fertilizer solutions and microbial solutions were added to the Biolog OmniLog automated analysis system, with sterile water serving as the control. The nutrient carrier’s capacity to support strain resistance was tested in 15 min frequency for 48 h. Field trials of the composite bioorganic fertilizer were conducted on bacterial wilt-infected soils in Fuquan and Huangping, Guizhou. During the tobacco seedling establishment phase, holes of 15 cm deep and 10 cm away from the base of each plant were dug and filled with 100 g of bioorganic fertilizer, with untreated soil serving as the control. Wilt incidence was assessed 70 days after transplanting. Tobacco yield and economic value were quantified after harvest. Soil samples were collected to determine R. solanacearum counts, and analyze the characteristics of the microbial community.

Results Optimal fermentation nutrient carriers for strains Y364, Y832, and Y878 were vermicompost∶vinasse∶cow manure∶rapeseed cake mass ratio of 1∶1∶1∶1. Their amplified counts in the fermentation medium reached 10⁹, 10⁸, and 10⁹ CFU/g soil, respectively. For strains Y835 and Y391, the organic fertilizer mass ratio in the nutrient carrier was 1∶2∶1∶1, achieving proliferation levels of 10⁹ CFU/g soil. The individually fermented microbial fertilizers were blended in a 1∶1∶1∶1∶1 mass ratio to form a composite bioorganic fertilizer. Compared to the control, field applications of this composite fertilizer in Fuquan and Huangping reduced tobacco bacterial wilt incidence by 10.72 and 9.29 percentage points, respectively, with control efficiencies of 58.01% and 61.29% respectively. Tobacco leaf yields increased by 37.33% and 91.27% respectively, while chemical composition scores improved by 6.97 and 3.37 points respectively. Soil R. solanacearum counts decreased by 3.85×10⁷ and 8.19×10⁷ CFU/g soil respectively, with significant alterations observed in soil microbial community structure. At the family level, the Fuquan trial site exhibited enrichment of microbial groups including Acidobacteriaceae, Terriglobales, Terriglobia, Acidimicrobiaceae, Acidimicrobiales, and Treboniaceae in the biofertiliser-treated soil. The Huangping trial site primarily enriched microorganisms such as Geodermatophilaceae, Geodermatophilales, Mycobacteriaceae, and Thermomonospora.

Conclusions The five antagonistic bacterial strains that were isolated and identified, exhibited high resistance to tobacco bacterial wilt and demonstrated rhizosphere chemotaxis characteristics. The composite bio-organic fertilizer, developed by fermenting each strain in its optimal nutritional carrier and then mixing them together, achieved prevention and control effects against tobacco bacterial wilt of 58.01% and 61.29% in Qiannan and Qiandongnan regions of Guizhou Province, respectively. Meanwhile, tobacco leaf yields increased by 37.33% and 91.27% in these regions, and the population of the bacterial wilt pathogen in the soil decreased by 1 to 2 orders of magnitude. The application of this compound bio-organic fertilizer significantly altered the soil microbial community structure, leading to a notable enrichment of beneficial microbial groups such as Nitrospirota, Bacillota, Actinobacteria, and Chloroflexi. Therefore, the bio-organic fertilizer centered around this composite microbial community is an excellent product for preventing and controlling tobacco bacterial wilt and enhancing the profitability of tobacco fields in Guizhou.