Trichoderma induces bacterial wilt resistance through synergistic activation of salicylic acid and ethylene signaling in tomato plants.

Bacterial wilt is one of the most devastating plant diseases affecting economically important crops globally. Several biocontrol agents have been investigated for the control of this disease. Most studies are limited to initial screening or preliminary investigations of disease-suppression efficacy. Investigations into the mechanisms by which the biocontrol agents modulate plant responses are rarely reported. This study investigated the mechanism by which Trichoderma harzianum alters plant hormonal responses. Initially, the roles of two hormones, SA and ET, were confirmed by using SA- and ET-impaired plants. Results showed that both hormones play a significant role in disease suppression. The impaired plants, when inoculated with the pathogenic bacteria, developed more severe disease than the wild-type plants. Application of Trichoderma increased the expression of SA- and ET-related genes, with significantly higher expression observed in wild-type plants compared to hormone-impaired mutants. Plants with enhanced expression of SA and ET showed increased disease suppression and higher activities of antioxidant enzymes. These plants exhibited a significant reduction in oxidative stress and produced higher content of SA and ET. These findings suggest that Trichoderma application enhanced SA and ET signaling, thereby increasing plant defense against bacterial wilt. This study highlights the role of plant hormones in disease suppression and how they can be manipulated to improve management strategies.