Biocontrol activity and action mechanism of Pseudomonas aurantiaca ST-TJ4 against Verticillium dahliae, the causal agent of Acer truncatum wilt.

Acer truncatum wilt caused by Verticillium dahliae is a severe soilborne disease that poses a threat to the cultivation of this plant in China. The present study explored the biocontrol efficiency and underlying antagonistic mechanism of Pseudomonas aurantiaca ST-TJ4 against V. dahliae. In vitro, strain ST-TJ4 exhibited excellent inhibitory effects on V. dahliae, causing mycelial deformation. This strain significantly suppressed the production of V. dahliae conidia and microsclerotia. Moreover, the application of ST-TJ4 reduced the incidence of Verticillium wilt in A. truncatum saplings in both the prevention group and the cure group. Comparative transcriptomic analyses revealed that ST-TJ4 induced differential expression of numerous genes in V. dahliae, most of which were downregulated. These differentially expressed genes were associated with cell wall-degrading enzyme activity, sterol biosynthetic processes, glutathione S-transferase activity, iron ion and sugar metabolism, and oxidoreductase activity. Further transcriptomic analyses of physiological indices indicated that ST-TJ4 significantly inhibited the synthesis of pectin lyase, endo-β-1,4-glucanase, melanin and soluble sugars of V. dahliae and had a stronger inhibitory effect under iron deficiency. Taken together, these data highlight P. aurantiaca ST-TJ4 as a promising biocontrol agent against A. truncatum Verticillium wilt.