Trichoderma controls bacterial blight caused by Xanthomonas axonopodis pv. passiflorae in Passiflora edulis

Several Trichoderma species are recognized as biocontrol agents that can enhance plant defenses against a wide range of biotic and abiotic stresses. However, few studies have investigated Trichoderma activity against bacterial pathogens, and the Xanthomonas axonopodis pv. passiflorae (Xap)-Passiflora edulis pathosystem remains largely unexplored.

We analyzed the effects of cell-free filtrates from Trichoderma cultures on the growth of Xap. We also investigated the potential of T. asperellum T25 and T. harzianum T146, when applied to the plant growth substrate, to control bacterial blight caused by Xap in P. edulis, as well as the mechanisms underlying systemic defense responses in the host plant. Fifty-day-old plants grown in substrate treated or untreated with a Trichoderma strain were inoculated or not with Xap, and changes in the expression of marker genes representative of jasmonic acid (JA) biosynthesis (LOX2), salicylic acid (SA)-dependent (PR1), and ethylene (ET)-dependent (PDF1.2) defense pathways were analyzed at 48 h post-inoculation (hpi) and 14 days post-inoculation (dpi). At 14 dpi, H₂O₂ content and the activities of three antioxidant enzymes -superoxide dismutase, peroxidase, and catalase- were also evaluated.

Trichoderma filtrates showed antimicrobial activity against Xap. In the absence of the pathogen, strain T25 promoted the growth of P. edulis plants. Both Trichoderma strains controlled disease symptoms with similar efficacy. However, at the early stage of the P. edulis-Xap interaction, differential expression of SA- and JA-related genes was detected between T25-pretreated and T146-pretreated plants. Furthermore, at the later stage of the interaction (14 dpi), pretreatment with strain T146 increased ROS levels (measured as H₂O₂ content) in response to Xap, whereas the lowest oxidative levels were observed in plants inoculated with the pathogen alone. Our results demonstrate that T. asperellum and T. harzianum effectively control bacterial blight caused by a virulent Xap strain in P. edulis.