ABSTRACT The growing concern over the environmental and health impacts of chemical pesticides has reinforced the need for sustainable alternatives to control destructive plant pathogens. Biological control using Trichoderma species has emerged as a promising approach, but detailed evaluations of their antagonistic mechanisms remain essential for developing effective biocontrol products. This study investigates the in vitro antagonistic activity of a Moroccan strain of Trichoderma asperellum (KU987252), isolated from compost, against four major soilborne pathogens affecting several vegetable crops: Rhizoctonia solani, Fusarium oxysporum, Phytophthora sp., and Verticillium dahliae. This work represents the first evaluation of a T. asperellum strain simultaneously against these four key pathogens, providing a comprehensive understanding of its antagonistic spectrum. The objective was to determine the efficiency and mechanisms of antagonism through direct confrontation, volatile-mediated, and diffusible metabolite assays, as a crucial step toward the development of a biological product based on this strain. We hypothesized that the strain would express multiple antagonistic strategies, both in direct contact and at a distance, resulting in strong suppression of pathogen development. The results confirmed that T. asperellum significantly inhibited pathogen growth, with inhibition ranging from 55.3% against V. dahliae to 86.7% against F. oxysporum in direct assays. Spatial colonization reached 85% against F. oxysporum and 82% against Phytophthora sp., highlighting its strong competitive ability. In indirect assays, Phytophthora sp. showed the highest inhibition of sporulation (96.0%), while V. dahliae exhibited the greatest inhibition of germination (84.9%). These pathogen-specific responses demonstrate the versatility of T. asperellum through both contact and metabolite-mediated interactions. These findings emphasize both the originality and applied potential of this Moroccan strain. By demonstrating its broad-spectrum antagonism, this study lays the foundation for developing compost-derived T. asperellum as a biocontrol product for sustainable tomato disease management. Keywords: Trichoderma asperellum, antagonism, inhibition, soilborne pathogens, sporulation, germination, mycelial growth.