In vitro Evaluation of Trichoderma viride Efficiency in Inhibiting the Growth of Alternaria alternata, the Causal Agent of Tomato Leaf Spot

Abstract

This research was conducted to evaluate the biocontrol efficiency of the antagonistic fungus Trichoderma viride, which was obtained from the Agricultural Research Center in Tripoli, Libya. The study aimed to assess its ability to inhibit and suppress the pathogenic fungus Alternaria alternata, the causal agent of leaf spot disease on tomato plants. The pathogen was originally isolated from infected tomato leaves collected from Wadi Souf Al-Jein farm in the Bani Walid region during the year 2025. The experimental procedures involved the isolation, purification, and identification of the pathogen based on its morphological characteristics, such as dark olive-to-black colonies and specialized conidiophores with transverse and longitudinal septa. The antagonistic activity was tested using the Dual Culture Plate Test on Potato Dextrose Agar (PDA) medium. The results of the study demonstrated a significant high antifungal potential of T. viride against A. alternata, achieving an inhibition rate of 87%. While the pathogen covered 100% of the plate in the control treatment, it only managed 13% growth in the presence of the bio-agent. Microscopic examination revealed the primary mechanism of antagonism as direct mycoparasitism. The hyphae of T. viride were observed coiling around the mycelium of A. alternata, leading to the degradation and destruction of the pathogen's mycelium. These findings are attributed to the ability of Trichoderma species to produce inhibitory substances and lytic enzymes such as chitinase and protease. The study concludes that T. viride is a highly effective and environmentally safe alternative to chemical pesticides for managing tomato leaf spot disease.