Toward quantitative modeling of the indirect interaction between Trichoderma spp. and foliar parasitic fungi

This paper introduces a Trichoderma-Mediated Parasite Inhibition (TMPI) model. We present a mechanism-based model for the interaction between a plant (e.g., grapevine), a root-associated Trichoderma fungus (e.g., Trichoderma asperelloides), and a foliar parasitic fungus (e.g., powdery mildew). The model focuses on cases where Trichoderma and the parasite do not interact directly. Instead, it captures (i) the plant’s response to infection, (ii) the systemic resistance triggered by Trichoderma, and (iii) the shift of Trichoderma between mutualism and parasitism. Stability, identifiability, and sensitivity analyses show that the model is suitable for fitting field data and for informing biocontrol strategies that promote sustainable agriculture and clarify Trichoderma dynamics. The stability analysis provides explicit, interpretable conditions for parasite eradication or persistence. The parasite is removed if both fungi fail to invade or if Trichoderma invades and prevents parasite establishment. Persistence requires the parasite reproduction number to exceed a threshold and, in coexistence scenarios, remain below a specific upper bound. If this bound is exceeded, the system exhibits oscillations involving the parasite. These dynamics reflect a shifting balance between host defense and parasite pressure, consistent with the Red Queen hypothesis. Parasite exclusion is possible when Trichoderma dominates and systemic resistance is strong relative to resource limitations.