Characterization of fungal extracts from Trichoderma isolates: their effects against coffee wilt pathogen (Gibberella xylarioides)
The current research work was designed to evaluate, test, and characterize effective antifungal extracts from Trichoderma isolates against coffee wilt pathogen (Gibberella xylarioides). For extraction of antifungal extracts from fungal mycelium different organic solvents, viz., chloroform, ethanol, methanol, ethyl acetate, n-hexane and butane were used. A direct bioautographic procedure was conducted, involving spraying suspension of Fusarium xylarioides on Thin Layer Chromatography (tlc) plates developed in solvents of varying polarities to detect a number of antifungal substances present in the extracts. Moreover, in vitro antagonistic bioassays were performed to evaluate and determine the potentiality of Trichoderma isolates as biocontrol agents against F. xylarioides. Antifungal extracts were successfully extracted from malt extract agar medium with all organic solvents used except from hexane. Bioautography assay revealed 60 zones of inhibition spots and the highest inhibition zone was observed in aut5 (51 mm) and aut6 (44 mm) with ethanol extract at Rf value of 0.43. In in vitro bioassay, the highest mean inhibitory effect on the growth of the pathogen was achieved by aut2 (77.4%) isolate in dual culture. In general, tlc-directed bioautography assay was found to be useful in isolating active compounds with antifungal activity and all Trichoderma isolates significantly reduced mycelial growth of the test pathogen compared to the control under in vitro condition.