Study on a temperature-dependent selective soil treatment agent in regulating tobacco rhizosphere microbial community and controlling root and stem diseases.

INTRODUCTION: This study investigated the effects of a selective soil treatment agent on the microbial community structure of tobacco rhizosphere soil and the photosynthetic performance of tobacco plants at different temperatures (15 °C, 25 °C, 35 °C) through pot experiments.

METHODS: The control efficacy against black shank and root rot diseases was also evaluated.

RESULTS AND DISCUSSION: The results indicated that 25 °C was the optimal temperature for the agent's effectiveness. Under this condition, the agent significantly inhibited the enrichment of phytopathogenic fungi such as Fusarium spp. in the rhizosphere soil (the abundance of Fusarium in the T25SJ treatment decreased by 78.6% compared to the untreated group T25CK), while optimizing the microbial community structure, as evidenced by increased fungal α-diversity (Shannon index) and enhanced competitiveness of beneficial bacteria (e.g., Pseudomonas spp.). Notably, the bacterial community stability was maintained (no significant change in the Simpson index), confirming the agent's selective regulatory effect rather than non-specific sterilization. Fluorescence imaging analysis revealed that the photosynthetic performance of tobacco plants treated with the agent at 25 °C was significantly higher than that of the untreated group, as showed by an increase in the maximum photochemical efficiency (Fv/Fm) (T25SJ vs. T25CK: 0.82 vs. 0.68), enhanced electron transport efficiency (ψ_Eo), and light energy conversion capacity (δ_Ro). In contrast, the untreated group exhibited severe damage to the photosynthetic system due to pathogen infection, leading to the inactivation of PSII reaction centers (increased ABS/RC and decreased RC/ABS values). At low (15 °C) and high (35 °C) temperatures, the agent still showed some inhibitory effects on certain pathogens (e.g., Thielaviopsis spp.), but the overall antibacterial efficiency and photosynthetic protection were significantly weaker than at 25 °C. Further analysis demonstrated that the agent alleviated oxidative stress caused by root damage and ensured the preferential allocation of light energy to photosynthesis by selectively suppressing dominant pathogens while preserving beneficial microbial populations. This study reveals that the antibacterial efficacy and photosynthetic protection of the soil treatment agent are significantly temperature-dependent, with 25 °C being the optimal application temperature. These findings provide a theoretical basis for the green control of soil-borne diseases in tobacco and the regulation of photosynthetic stress resistance, and offer a new paradigm for resolving the contradiction between "pathogen control" and "ecological protection" in soil-borne disease management.