Phytochemical characterization and antifungal activity of medicinal plant extracts against Colletotrichum species associated with anthracnose in Thailand

Colletotrichum is a major plant-pathogenic fungus responsible for anthracnose, a disease that significantly reduces crop yield and quality, thereby hindering commercial production. This study aimed to isolate, identify, and characterize Colletotrichum species associated with anthracnose in various fruits and ornamental plants in Thailand, using both morphological and molecular approaches. Subsequently, the medicinal plant extracts were evaluated for their antifungal activity against the isolated Colletotrichum species, and their bioactive compounds were profiled using GC-MS and LC-MS analyses. Eleven Colletotrichum isolates were obtained and identified as nine distinct species, namely C. asianum, C. brasiliense, C. fructicola, C. musae, C. nymphaeae, C. okinawense, C. orchidearum, C. pandanicola, and C. truncatum. Among the ten medicinal plants tested, only the ethanolic extract of clove (Syzygium aromaticum) exhibited strong antifungal activity against all fungal isolates. The extract exhibited minimum inhibitory concentrations as low as 12.5 mg/mL against C. okinawense and C. orchidearum, and 25 mg/mL against the remaining species. GC-MS profiling of the ethanolic clove extract revealed that 2-methoxy-4-prop-2-enylphenol (eugenol, 72.417%) was the predominant compound, followed by (1R,4E,9S)-4,11,11-trimethyl-8-methylenebicyclo [7.2.0] undec-4-ene (β-caryophyllene, 12.125%), and (2-methoxy-4-prop-2-enylphenyl) acetate (eugenyl acetate, 8.121%). Additionally, LC-MS profiling indicated that the extract contained several antifungal constituents, including quercetin, kaempferol, isorhamnetin, myricetin, gallic acid, ellagic acid, catechol, caffeic acid, p-coumaric acid, methyl trans-cinnamic acid, and resveratrol. These findings highlight the diversity among pathogenic Colletotrichum species in Thailand and establish that clove extract, which contains flavonoids, phenolics, terpenoids, and alkaloids, holds potential as an eco-friendly alternative for agricultural disease management.