Discovery and Development of Biocontrol Agents Against Major Plant Diseases

Abstract

Trichoderma species represent the most extensively studied and commercialized fungal biocontrol agents, exhibiting multifaceted mechanisms to suppress phytopathogens including enzymatic degradation, secondary metabolite production, direct mycoparasitism, and induced systemic resistance. These fungi contribute significantly to sustainable agriculture by reducing dependency on synthetic pesticides while enhancing plant health. Native Trichoderma species demonstrate superior efficacy compared to exotic strains due to their adaptation to local edaphic and climatic conditions. This study aimed to isolate, identify, and evaluate the biocontrol potential of indigenous Trichoderma isolates from Lebanese agricultural soils. From 69 soil samples collected across diverse regions, six Trichoderma isolates were recovered using a selective medium. Initial morphological identification was followed by molecular confirmation through PCR amplification of ITS, TEF1-α, and rpb2 gene regions with expected amplicon sizes of approximately 600 bp, ~1200 bp, and ~900-1000 bp, respectively. PCR optimization required gradient annealing temperature adjustment, touchdown PCR, and nested PCR protocols to achieve consistent amplification, with rpb2 using the nested PCR protocol demonstrating the highest reliability. Antagonistic activity was evaluated through dual culture assays against three economically important phytopathogens: Fusarium oxysporum f. sp. cubense Tropical race 4 (Foc TR4), Verticillium dahliae, and Botrytis cinerea. All isolates demonstrated high inhibition rates of 74.4–83.7% against Fusarium, 81.0–92.9% against Botrytis, and 75.0–84.4% against Verticillium, with direct mycoparasitism observed in selected isolates. These inhibition levels are comparable to the most effective strains documented in current literature. Pathogen susceptibility ranked as follows: Verticillium followed by Botrytis and Fusarium. Statistical analysis revealed highly significant effects of both Trichoderma isolate and pathogen type (p < 0.001), while strain-pathogen interaction was non-significant (p = 0.106). These findings demonstrate the exceptional biocontrol potential of native Lebanese Trichoderma isolates against major plant pathogens. Future research will focus on molecular identification to the species level through sequencing of the three amplified gene sequences, BLASTN analysis and construction of phylogenetic trees. The efficacy of the native Trichoderma isolates will be validated against a larger number of phytopathogens in greenhouse trials on economically important crops including tomatoes, cucumbers, and eggplants.