**4. Conclusions**

Plants affected by *F. oxysporum* reduce their growth due to the pathogen's ability to colonize roots, which prevents proper nutrition of the seedling and leads to death, causing losses in the producer in the first stage of tomato crop.

The evaluation of Mexican strains of *Trichoderma* spp. and its antagonistic effect on *F. oxysporum* on tomato seedlings (*L. esculentum* Mill) was determinant to verify their potential for biological control in a crop of great importance in the economy and the country's food.

The *T. harzianum* strain presented the highest growth rate with a mean of 1.25 cm/day, proving to be the most aggressive strain to control *F. oxysporum* with a development rate of 3.80 mm/day.

The three native strains of *Trichoderma* spp. present inhibition of radial growth on the Fo-A (*F. oxysporum*) strain, with *T. harzianum* being the most antagonistic (81.50%), in addition, the results of the interaction of the paired dual cultures to *F. oxysporum*, was very heterogeneous and highly significant statistic differences, where the *Trichoderma* isolates showed a zone of visible overgrowth with the *F. oxysporum* hyphae, which shows more aggressiveness on the part of the antagonistic fungus.

The efficacy shown by the native strains of *Trichoderma* spp. evaluated in this study against *F. oxysporum*, applied to tomato seedlings (*Lycopersicon esculentum* Mill), showed that *T. harzianum* obtained higher height, greater stem thickness and greater production of dry biomass, likewise, the treatment inoculated with *F. oxysporum* obtained the highest incidence (83%) and the lowest survival (17%) of germination in greenhouse conditions.
