Dual stress defense? Evaluating Trichoderma virens for cotton drought and insect resistance

Our goal was to analyze whether treating cotton plants with the endophytic fungus Trichoderma virens could promote drought and insect stress resistance. Four- to six-week-old cotton plants were inoculated via soil drench with 10 mL aqueous suspensions of T. virens spores (10⁷ spores/ml), while control plants received water only (n = 5 plants per treatment per trial). Endophytic colonization was confirmed, with >50% of surface-sterilized leaf, root, and stem samples from treated plants testing positive for T. virens at 7-, 14-, and 21-days post-inoculation (dpi). To assess drought tolerance, water was withheld beginning at 7 dpi, and time to wilting and death was recorded. In a separate cohort, above- and belowground biomass were measured to assess growth effects. Additionally, herbivore performance was evaluated using cotton aphids (Aphis gossypii) and fall armyworm (FAW, Spodoptera frugiperda, strains R and C). Aphid population growth was monitored over two weeks, while FAW larvae were reared individually on treated or untreated plants until adult death. While fungal treatment did not significantly alter plant biomass or reduce aphid or FAW performance, there was a non-significant trend toward lower aphid populations on treated plants. In contrast, T. virens-inoculated plants exhibited significantly improved drought tolerance, surviving longer under water stress. These findings suggest that T. virens can enhance cotton resilience to abiotic stress through endophytic colonization, though its benefits for herbivore resistance and growth promotion appear limited under the tested conditions.