This study demonstrated the efficacy of riboflavin and Trichoderma spp. In increasing the induction of resistance in tomato plant against the pathogenic fungus Alternaria alternata that causes Alternaria spot disease. The study in Invetro showed the ability of two isolates of the pathogenic fungus A.alternata in the water agar medium, as the isolate of fruits had the most impact on the severity of infection of tomato seeds, which amounted to 59% compared to isolate the leaves, which amounted to 47%. The results of the antagonism test for T.viride and T.koningii in PDA medium showed a high antagonistic ability against A.alternata by double culture method, where the antagonism degree was 1 according to the Bell scale. Many chemical compounds were obtained from the filtrate of T.viride and T.koningii by GC-MS technique believed to have a role in inhibiting pathogens, including 2-Propenoic acid and Octadecanoic acid. The bio-resistant fungi and riboflavin used reduced the severity of infection with the pathogen. A. alternata in pots had the lowest severity of infection with riboflavin treatment (8.21)%. The highest content of peroxidase enzyme in tomato leaves when T.v+T.k+B2+A.a treatment was 3.30 units/gm.

.