Exploring the antifungal activities of secondary metabolites of Trichoderma harzianum against the leaf spot pathogen of turmeric Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.

The present study aimed to evaluate the antifungal activity of Trichoderma harzianum against Colletotrichum gloeosporioides, the causal agent of turmeric leaf spot. The pathogen was isolated from symptomatic turmeric leaves and identified using morphological traits and amplification of the ITS region, followed by sequencing. Pathogenicity was confirmed via Koch's postulates. Various biocontrol agents were tested in vitro, and T. harzianum exhibited the highest inhibition (75.92%) in dual culture assays. Crude culture filtrates of T. harzianum also inhibited the pathogen in a seeded agar assay, showing 22.22% inhibition. GC-MS profiling was carried out to identify the bioactive compounds responsible using the culture filtrates of T. harzianum, the pathogen, and their interaction. A total of 129 metabolites were identified, including phenolic acids, fatty acids, esters, and phthalates with reported antimicrobial activity. The interaction revealed compounds common to both organisms, suggesting biochemical cross-talk. This study demonstrates the potential of T. harzianum as an effective biocontrol agent against C. gloeosporioides and highlights key antifungal metabolites involved. Further characterisation of these compounds may support the development of bioformulations for eco-friendly disease management.