Alterations in Mycelial Morphology and Flow Cytometry Assessment of Membrane Integrity of Ganoderma boninense Stressed by Phenolic Compounds

SIMPLE SUMMARY: Oil palm is an important cash crop in the tropics, producing 3–8 times more oil than any other oil crop. Basal stem rot (BSR) disease caused by Ganoderma spp is one of the greatest threats to oil palm producing countries, leading to economic losses. The pathogen infection has a lethal effect on oil palm by degrading the xylem and tissues of the palm bole, which subsequently restricts water and nutrient uptake from the roots to the upper parts of the palm, leading to stress and making it vulnerable to further saprophytic microbial attack. The progression of the disease is very slow; however, every infected plant eventually dies and, hence, Ganoderma is known as the ‘silent killer’ of oil palm. There are lots of strategies that have been tested and carried out by the researchers to overcome the losses caused by BSR; however, little success has been achieved. This study assessed naturally occurring phenolic compounds as a green control measure to suppress the pathogen and identify their effect on the cell membrane potential as a possible mechanism of suppression. The utilization of phenolic compounds may help in reducing the usage of synthetic fungicides and produce less impact on the environment. ABSTRACT: Global increase in demand for palm oil has caused an intensification in oil palm plantation; however, production is greatly hindered by Basal Stem Rot (BSR) disease caused by Ganoderma boninense. There are many approaches to controlling BSR, although, there is no accurate, sustainable and effective method to suppress G. boninense completely. Hence, four phenolic compounds [Gallic acid (GA), Thymol (THY), Propolis (PRO) and Carvacrol (CARV)] were selected to evaluate their antifungal effect, ability to alter the mycelium morphology, and fungal cell integrity against G. boninense. Significant differences (p < 0.05) were observed and 94% of inhibition was exerted by GA on G. boninense growth. Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy observations revealed that GA and THY treatment caused severe damage to the mycelium and recorded the highest amount of sugar and electrolyte leakage. The study of cell integrity and morphological disruption has elucidated the reduction of G. boninense cell viability. Generally, our findings confirm the fungistatic effects of GA and THY. The evolution of phenolic compounds during the phytopathology studies indicated their coherence in eradicating the G. boninense. It is proposed that GA and THY had the potential to be developed further as a natural antifungal treatment to suppress G. boninense.