Trichoderma -mediated host conditioning in plant viral pathosystems: evidence-weighted virological outcomes and unresolved antiviral checkpoints

Crop viral diseases are managed largely through prevention because established systemic infections are rarely reversible under crop conditions. This critical review evaluates how Trichoderma spp. and Trichoderma-derived inputs have been interpreted in plant viral pathosystems. We distinguish upstream host responses, including elicitation, priming, immune activation, and host conditioning, from virological outcomes, host-performance modifiers, and mechanistic confidence. Primary interpretation was restricted to studies reporting virus-specific endpoints, such as viral accumulation, viral DNA or RNA levels, titer, or movement. Current evidence is concentrated in cucumber mosaic virus, tobacco mosaic virus, and potato virus Y systems, with beet curly top Iran virus and tomato leaf curl Palampur virus extending the evidence base to single-stranded DNA viruses. Across retained studies, prechallenge Trichoderma treatments support host conditioning, and several systems show reduced viral burden relative to infected controls. However, virological restriction often co-occurs with improved host performance or defense-associated responses, making the phenotype composite rather than checkpoint-resolved. No convincing case of tolerance at comparable viral burden was identified. Future progress requires integrated designs linking fungal establishment, viral dynamics, host performance, mechanistic checkpoints, and transmission-relevant outcomes.