Basal stem rot (BSR), a devastating disease caused by the white-rot fungus Ganoderma boninense, poses a critical economic threat to the oil palm (Elaeis guineensis) industry, particularly in Malaysia and Indonesia where 85% of global palm oil is produced. Because conventional control methods often fall short, this study systematically evaluated the antagonistic efficacy of natural, eco-friendly phenolic compounds—specifically gallic acid (GA), thymol (THY), propolis (PRO), and carvacrol (CARV)—as potential alternatives to synthetic chemical fungicides. Fungal mycelia were exposed to these compounds to assess their biochemical and structural impacts. Utilizing High-Resolution Transmission Electron Microscopy (HR-TEM), flow cytometry with propidium iodide (PI) staining, and electrolyte leakage assays, the researchers monitored cellular and membrane integrity under stress conditions. Additionally, both qualitative and quantitative profiling of vital hydrolytic and ligninolytic enzymes (such as cellulase, amylase, xylanase, and peroxidases) were conducted to determine the underlying biochemical mechanisms of inhibition, with all data rigorously validated using Tukey's Studentized Range (HSD) Test in SAS software. The results revealed that these phenolic compounds exert a powerful, multifaceted antifungal effect, causing severe concentration-dependent ultrastructural damage and morphological alterations, including cell wall destruction, vacuole fusion, and plasma membrane detachment (Figure 1). Among the tested treatments, gallic acid demonstrated the highest potency, inducing maximum electrolyte leakage (100.30µ mhos g-1 at 8mg/mL) and the highest cell mortality rate at 45.73%, closely followed by thymol at 31.90%, while propolis and carvacrol exhibited weaker effects. Flow cytometry confirmed that GA caused the most extensive cell membrane permeability and pore formation, with 33% dead cells showing strong nuclear staining. Furthermore, GA and THY significantly suppressed the radial growth of G. boninense and effectively inhibited the production of essential ligninolytic enzymes, notably lignin peroxidase (LiP) and manganese peroxidase (MnP), which the fungus requires for host tissue colonization. In conclusion, gallic acid, followed by thymol, serves as a highly effective inhibitor that disrupts membrane integrity, induces oxidative stress, and suppresses enzymatic activity, highlighting its strong potential as a sustainable, natural fungicidal agent for managing basal stem rot disease in the oil palm industry.

Figure 1. HR-TEM images (6000x) showing ultrastructural changes in G. boninense PER 71 hyphae after phenolic compound treatments. (A) Healthy hyphae with intact cell wall, plasma membrane and visible organelles. (B) GA treatment showing disrupted walls and membranes, empty regions, condensed nucleus and deformed mitochondria. (C) Thymol-treated hyphae displaying membrane disruption and cytoplasmic leakage. (D) Propolis-treated hyphae with disrupted membranes and visible organelles. (E) Carvacrol-treated hyphae showing minimal damage and intact structures. Scale: 1 µm

Reference:

Ganapathy, D., Vadamalai, G., Siddiqui, Y., Ahmad, K., Ling, K. L., & Adzmi, F. (2025, August 20–21). Phenolic compounds as antagonists in altering mycelial morphology and enzyme activity of G. boninense. In Proceedings of the 3rd International Conference on Plantation Technology (ICPTech2025): Vol. 2. Plantation Studies (pp. 49–53).

Date of Input: 29/05/2026 | Updated: 29/05/2026 | ainzubaidah