Ganoderma butt, stem and root rot in coconut, rubber and tea

Introduction

Ganoderma butt rot or basal stem rotis mainly a problem in coconuts, being caused by G. boninense Pat., G. tornatum (Pers.) Bresad., occasionally G. zonatum Murrill. and G. philippii. These fungi can also be pathogens of rubber and tea, commonly known as red root disease. In addition Ganoderma species can cause internal decay in a range of hardwood and softwood tree species.

Symptoms

Palms - The lower older fronds initially show symptoms where the pinnae wilt, roll back and eventually the entire frond droops parallel to the trunk. Tree vigour is reduced, and leaf growth remains poor for several years. Unopened spears may remain in the crown of the canopy, flowering is reduced and nut set is reduced and fruit small and distorted. In time, only one or two spears will remain, these die, then the head of the palm may fall off or the trunk may collapse. The process may take 3-4 years. The trunk decays internally and basidiocarps may appear on the lower trunk soon after decline symptoms began.

Rubber - Infected rubber plants initially express symptoms in the foliage, which yellow, turn brown and fall. The pathogen can be recognised by its rhizomorphs, which begin as creamy white, to light red, then becoming dark-red to black with age. The wood of the host then turns into a watery sponge. The upper surface of fruiting bodies is dull brown with a white margin, grooved or covered with large knobs. The undersurface is white with pores.

The Pathogen

Ganoderma is a basidiomycete fungus, commonly known as a bracket fungus. It is a polypore fungus, in which the most prominant phase is the fruiting structure which is a bracket structure found on the side of the host plant. Spores are released in great numbers from this fruiting structure. The main mass of the fungus is hyphae found internally in the trunk of the host.

Distribution

This disease has not yet been documented in Vietnam.

Host Range

Rubber, tea, coconut and other palms. A range of tree species may be affected.

Epidemiology

The pathogen is spread via airborne basidiospores, root contact with infested soil, and root graft transmission. It can spread horizontally in the soil up to around 2m from diseased to healthy host roots. Basidiospores infect wound sites on trunks or the cut ends of palm fronds.

Control

Disease can be minimised by limiting the spread of the pathogen in contaminated soil, wide palm spacing to prevent root grafts and minimising injury to palms will reduce infection. All infected material should be removed hygienically from the plantation.

Botanic Gardens Trust, Sydney, Australia

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