Altered Cytostructure and Lignolytic Enzymes of Ganoderma boninense in Response to Phenolic Compounds

Ganoderma boninense is a white-rot fungus that causes basal stem rot (BSR) disease in the oil palm. Potential natural inhibitors, such as gallic acid, thymol, propolis, and carvacrol, were assessed for their antagonistic effects against G. boninense. These naturally occurring phenolic compounds have also been utilised to inhibit hydrolytic and ligninolytic enzymes produced by the pathogen. Mycelial inhibition was dose-dependent in the presence of different concentrations of phenolic compounds, including, for example, in cellulase enzyme inhibition (GA mg/mL = 94%, THY 0.25 mg/mL = 90%, PRO 3.5 mg/mL = 92.5%, and CARV 0.15 mg/mL = 90.3%). A significant difference was observed revealing that gallic acid had the greatest inhibitory effect on the secretion of hydrolytic and ligninolytic enzymes, especially at 40 mM GA (cellulase = 0.337 U/mL, amylase = 0.3314 U/mL, xylanase = 0.211 U/mL, laccase = 0.4885 U/mL, lignin peroxidase = 0.218 U/mL, and manganese peroxidase = 0.386 U/mL). The growth and secretion of enzymes (inhibitory action) are inversely proportional to the concentration of phenolic compounds. Phenolic compounds have a greater potential as inhibitory agents and suppress the