Additive effects of Trichoderma gamsii T6085 and Clonostachys rosea IK726 enhance Fusarium head blight control in wheat.

Biological control is a sustainable strategy for crop protection which reduces chemical input. Biological control thus addresses the challenges of global population growth, climate change, and food security. The modern framework of bioprotection encompasses biological control agents (BCAs) which are living organisms and viruses that actively target pathogens. Effective biocontrol requires three essential components: the pest, the BCA(s), and the plant host. Plant pathogens account for up to 40% of pre- and post-harvest losses, including yield reduction and mycotoxin contamination. Fusarium head blight (FHB) in wheat is caused primarily by Fusarium graminearum (Fg). This disease has increased in Europe over the past 30 years. Conventional fungicides provide limited protection and raise concerns about sustainability and food safety. Biological Control Agents (BCAs) offer eco-friendly alternatives by suppressing pathogens, enhancing crop resilience, and contribute to meeting the UN Sustainable Development Goals and the European Grenn Deal initiatives that promote integrated pest management (IPM). BCA efficacy under field conditions is influenced by plant genotype, environmental stresses, and production or formulation limitations. Multi-strain or combined BCA approaches have emerged as promising solutions. Co-inoculation or sequential application of compatible BCAs can exploit functional complementarity, enhance stress tolerance, colonization of rhizosphere and phyllosphere, and stabilize disease suppression. Combined application may also integrate chemical, physical, or elicitor-based treatments. Fungal BCAs, particularly Trichoderma and Clonostachys species, are versatile and environmentally adaptable, capable of endophytic colonization, inducing systemic resistance, and directly antagonizing pathogens. T. gamsii T6085(Tg) and C. rosea IK726 (Cr) are model isolates for FHB management. T6085 significantly reduced the disease severity by 57% when applied to wheat spikes at anthesis, without major impact on the wheat microbiome. IK726 was effective as seed coating or foliar spray, reducing FHB severity by up to 50% and lowering DON levels by 30%. Both isolates demonstrated, when used alone, broad activity across cereals. FHB complexity, due to pathogen diversity, narrow host susceptibility, and environmental variability, necessitates integrated approaches. Combining Tg and Cr was hypothesized to improve disease control, stabilize performance, and exploit complementary mechanisms. In vitro and in planta assays showed minimal antagonism between isolates, while both differentially modulated defence-related genes in the host depending on tissue and timing. Application of Tg + Cr differently upregulated Lox1 and PGIP2, on healthy and infected spikes, respectively. These mechanisms were observed already at 72 hpi with the BCAs alone and at 24 hpi in presence of the pathogen. At growth chamber scale the co-inoculation reduced FHB symptoms by 93% and perithecia development by 96%. Greenhouse trials confirmed improved performance given by the co-inoculation, assessing a reduction in disease incidence and severity of about 45%. Disease progression was slowed down only by the combined inoculation, and it also stabilized variability among replicates, suggesting a more consistent performance. Fg DNA abundance was reduced by 94% and the co-inoculation boosted Cr biomass production. DON level was reduced by 59% as well as the damaged kernels and finally the 1000-kernel weight was increased by 28% by Tg + Cr. Additive effects were confirmed via Bliss Independence model. In conclusion, co-application of Tg and Cr represents a robust and sustainable FHB management strategy. By leveraging additive effects, complementary modes of action, and modulation of host defence response, this approach consistently enhances disease suppression, improves grain quality, and reduces mycotoxin accumulation. Integration to IPM programmes should reduce chemical input, enhance crop resilience, and contribute to sustainable cereal production. Future work should focus on early-stage mechanistic interactions, optimized inoculation protocols, and large-scale field evaluation to further integrate these BCAs into advanced sustainable management strategies.