Trichoderma harzianum strain T22 enhances direct and indirect defenses in tomato plants against the stink bug Halyomorpha halys

BACKGROUND: Plant interactions with beneficial microbes can modulate defense responses against insect herbivores, yet the mechanisms remain poorly understood for herbivorous stink bugs. This study evaluated the impact of the plant growth-promoting fungus, Trichoderma harzianum T22, on direct and indirect defenses of tomato plants challenged by the invasive stink bug Halyomorpha halys. RESULTS: Inoculation of tomato plants with T. harzianum T22 reduced the relative growth rate of H. halys nymphs, accompanied by enhanced expression of defense-related genes involved in the jasmonic acid and salicylic acid pathways, notably ToPIN2, ToLOXD and ToPR1. Behavioral assays revealed that females of the egg parasitoid Trissolcus japonicus, one of the main natural enemies of H. halys, were more strongly attracted to volatiles emitted from inoculated plants induced by stink bug feeding and oviposition. However, no effect of fungal inoculation was detected in the chemical composition of plant volatiles. CONCLUSION: These findings demonstrate that T. harzianum T22 enhances tomato responses against H. halys by strengthening defense signaling pathways and modulating indirect defenses that facilitate natural enemy recruitment. Overall, these results suggest that using plant-growth-promoting fungi to enhance plant defenses is a promising crop protection strategy for controlling stink bug pests.