Pectobacterium carotovorum subsp. carotovorum (Pcc) is a major phytopathogen responsible for soft rot in vegetables, affecting various staple crops such as carrots and potatoes. However, the recent emergence of streptomycin-resistant strains of Pcc has compromised the effectiveness of streptomycin for treating disease in agriculture. This study aimed to evaluate the effects of the phenolic compounds carvacrol, streptomycin, and a combination of both on the antibacterial activity, cell membrane integrity, and virulence factors of a streptomycin-resistant strain of Pcc (SP). The results revealed that the minimum inhibitory concentrations (MIC) of carvacrol and streptomycin against the SP strain were 200 μL/L and 50 g/L, respectively. In particular, their combined application had an additive effect on SP (fractional inhibitory concentration index, FICI = 0.625), leading to 2-fold and 8-fold reductions in the concentrations of the combined use of carvacrol and streptomycin, respectively, compared to when used alone. Follow-up control tests using detached Chinese cabbage, potato, and carrot samples showed that the combined treatment significantly alleviates the severity of soft rot disease and inhibits the relative conductivity, motility, and extracellular hydrolase secretion of SP. The scanning electron microscopy and confocal laser scanning microscopy observations further confirmed the disruption of SP’s cell membrane permeability and cell wall integrity after treatment with both carvacrol and streptomycin. Additionally, the transcriptome analysis indicated that their combined use enhanced the suppression of SP by regulating genes associated with its membrane integrity, virulence factors, and resistance mechanisms. In conclusion, applying the phenol–antibiotic combination of carvacrol and streptomycin significantly reduces the streptomycin dose needed against SP and can effectively control soft rot in vegetables prone to it, offering a potential management strategy for controlling SP-induced soft rot during postharvest storage.

Soil salinization impacts over one billion hectares, threatening global food security. Here, a salt-tolerant bacterial strain, Pseudomonas fluorescens G3, was isolated from the rhizosphere of maize (Jinongyu-719) growing in saline–alkali soils in Gansu Province, China. This strain demonstrated the ability to secrete indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, and extracellular polysaccharides. It also exhibited notable phosphate-solubilizing activity and robust siderophore production capabilities. Under salt stress conditions (200 mM NaCl), the P. fluorescens G3 strain significantly improved maize’s growth parameters, namely its plant height, root length, and dry weight. Further, it enhanced antioxidant enzyme activity while reducing the accumulation of malondialdehyde (MDA), mitigating stress-induced oxidative damage. In P. fluorescens G3-inoculated plants, leaf and root Na⁺ contents decreased by 34.90% and 33.91%, while their K⁺ contents increased by 40.20% and 33.47%, respectively. Inoculation with P. fluorescens G3 enhanced taxonomic richness (ACE, Chao1) and evenness (Shannon, Simpson) in the rhizosphere bacterial community, leading to a significantly greater relative abundance of several bacterial genera: Pseudomonas, Methylophaga, Enhygromyxa, Desulfuromonas, and Devosia. These shifts in the microbial community composition suggest a potential restructuring of functional profiles, possibly enhancing processes beneficial to plant salt tolerance, such as ion homeostasis and stress mitigation: the biosynthesis of cofactors and secondary metabolites; bacterial secretion and two-component systems; porphyrin metabolism; flagellar assembly; biofilm formation; and bacterial chemotaxis. Redundancy analysis revealed positive correlations between microbial composition at both the phylum and genus levels and the activity of stress resistance enzymes after treatment with Pseudomonas fluorescens. This study provides important theoretical foundations and microbial resources for utilizing microbial community regulation in saline–alkali soil bioremediation.

Phytophthora blight, caused by Phytophthora capsici, an oomycete pathogen belonging to the phylum Oomycota, is a major soil-borne disease that limits the cultivation of pepper (Capsicum annuum). In this study, the bacterium Serratia plymuthica MM was evaluated for both its antagonistic ability and plant growth-promoting (PGP) potential. The sterile fermentation filtrate of S. plymuthica MM exhibited strong antifungal activity in vitro, inhibiting the mycelial growth of P. capsici by up to 88.32%. In pot experiments, Serratia plymuthica MM significantly reduced both disease incidence and disease severity of Phytophthora blight in pepper plants, achieving control efficacies of 88.33% (preventive application) and 55.56% (therapeutic application). Microscopic observations revealed severe hyphal abnormalities, including distortion, shrinkage, collapse, and fragmentation. Furthermore, propidium iodide (PI) and DAPI double staining provided cellular-level evidence of antifungal activity, demonstrating concentration-dependent disruption of membrane integrity and nuclear organization in P. capsici hyphae, which was supported by pronounced increases in ion leakage from pathogen cells. Further, S. plymuthica MM exhibited PGP traits, including nitrogen fixation, phosphate solubilization, siderophore production, and indole-3-acetic acid (IAA) synthesis. Pot experiments using the pepper cultivar ‘Longjiao’ (Capsicum annuum L. cv. Longjiao) confirmed significant growth promotion and enhanced activities of key defense-related enzymes (POD, PPO, PAL, and CAT). Stable colonization of pepper roots was verified by green fluorescent protein (GFP) labeling, demonstrating the strain’s persistence in the rhizosphere. Collectively, these results highlight the dual role of S. plymuthica MM in suppressing P. capsici and promoting pepper growth, supporting its potential as an eco-friendly biocontrol agent for sustainable pepper production.