Abstract
Abstract Endophytic fungi play an important role in promoting plant growth by producing phytohormones and enhancing nutrient availability; however, their functional roles in orchids remain poorly understood. This study aimed to isolate and functionally characterize plant growth-promoting (PGP) endophytic fungi associated with Vanda tessellata (Roxb.) Hook. ex G.Don. Six representative endophytic fungal isolates were evaluated for plant growth-promoting traits, among which isolate KU/BOT/VT004 exhibited the highest activity. Based on morphological characteristics and ITS rDNA sequence analysis, the isolate was identified as Colletotrichum cf. cobbittiense. The isolate produced high levels of indole-3-acetic acid (35.05 µg/mL), along with ammonia and siderophore activity, indicating strong nutrient-mobilizing potential. Application of the fungal culture filtrate to in vitro-grown protocorms resulted in a two- to three-fold increase in biomass and significantly enhanced chlorophyll content compared with untreated controls. Filtrate-treated protocorms also maintained sustained growth beyond 60 days, whereas nutrient-limited control protocorms exhibited reduced growth. These findings demonstrate the growth-promoting potential of metabolites produced by isolate KU/BOT/VT004 and suggest that this endophytic fungus is a promising candidate for future bioinoculant development and orchid propagation, pending further validation through fungal inoculation and colonization studies.