Basal stem rot of oil palm (Elaeis guineensis); mode of root infection and lower stem invasion by Ganoderma boninense

Abstract

Reproducible infection of intact roots of oil palm (Elaeis guineensis) with Ganoderma boninense, the cause of basal stem rot, showed penetration followed by rapid longitudinal progression of hyphae and colonization of the lower stem (bole). Light and transmission electron microscopy showed invasion of the root cortex, with no evidence of selective progression through the vascular system or lacunae. In newly colonized tissue the fungus behaved as a hemibiotroph, with numerous, wide, intracellular hyphae occupying entire host cells that possessed intact cell walls and contained discernible cytoplasm and organelles. In the bole this phase coincided with a complete depletion of previously abundant starch grains in advance of invasion. Subsequently, in the roots and colonized stem base, widespread necrotrophic, enzymatic attack of all layers of the host cell walls occurred. Hyphae were intra-and intercellular and intramural and associated host cell wall degradation was often at a distance from hyphae, resulting in cavities within cell walls. A third developmental stage was the formation of an extensive, melanized, tough mycelium or pseudo-sclerotium which surrounded roots and comprised many very thickwalled cells encasing more typical thin-walled hyphae. Macroscopic observation of and isolation from the bole of randomly felled, commercial palms provided confirmatory evidence that multiple infections originated in the roots before spreading into the base of long-established palms.

OIL PALM ROOTS COLONISATION BY Ganoderma boninense: AN INSIGHT STUDY USING SCANNING ELECTRON MICROSCOPY

“…Invasion of G. boninense in the root cortex as observed via SEM provides crucial evidence of cell wall degrading enzymes (CWDE) production by the fungi, which created a penetration holes through the cell wall layers allowing the entrance of G. boninense (Cooper, 1984). This finding is also supported by previous work by Rees et al (2009) which discovered penetration holes on the outer cell of oil palm root tissue through transmission electron microscopy (TEM). The invasion process of cell wall layer of oil palm root cells resulted from the development of multiple holes through localised area causing a complete breakdown of cell wall.…”

“…This article shows the route and progress of G. boninense colonisation after six months of Figures 1 and 2 complimented the study by Rees et al (2009). The growth habit of G. boninense hyphae observed along the walls of epidermal and cortex cells of oil palm roots is also similar to the study reported by Lopez-Llorca et al (2002) on colonisation of barley by Verticulum chlamydosporium.…”

“…G. boninense exploits a sequential biotrophic-and necrotropicinfection switch strategy to colonise its host plant, known as hemibiotrophs (Ho et al, 2016). During the initial infection of biotrophic phase, colonisation of Ganoderma occurs in root cortex with numerous hyphae occupying the entire host cells that have fully intact cell walls (Rees et al, 2009). Once biotrophic growth has been successfully established, the fungus switches to nectrotropic phase associated with extensive cell wall degradation, that kill and of invasion can be monitored.…”

About Ganoderma boninense in oil palm plantations of Sumatra and peninsular Malaysia: Ancient population expansion, extensive gene flow and large scale dispersion ability

“…This result may reflect the fact that date of planting has no impact on the selection of specific fungal genotypes. It could also suggest that the inoculum present in the soil remains from one generation to another, highlighted by many authors (Hasan and Turner 1998;Breton et al 2006;Rees et al 2009), is either not a major source of disease or has already a very high diversity level as suggested by Miller et al (1999). This absence of correlation between factors and selection of specific genotypes could thus be caused by an overall very high level of genetic diversity both present in airborne basidiospores and dead palm trunk and stumps dwelling inoculum.…”

In vitro growth of Ganoderma boninense isolates on novel palm extract medium and virulence on oil palm (Elaeis guineensis) seedlings

“…Furthermore, pseudosclerotial-like structures were noted covering the roots. These structures were also reported as survival organs for Ganoderma by Rees et al, (2009). Most of the literatures reported that the signs or symptoms for diseased seedlings only manifested approximately 3-4 months after treatments for 4 to 6-month-old seedlings (Breton et al, 2006, Nur Ain Izzati and Abdullah, 2008, Rees et al, 2007, Sariah et al, 1994.…”