Metrics details. Basal stem rot BSR caused by hemibiotroph Ganoderma boninense is a devastating disease resulting in a major loss to the oil palm industry. Since there is no physical symptom in oil palm at the early stage of G. Oil palm Elaeis guineensis seedlings were artificially infected with G. The host counter-attack was evidenced based on fungal hyphae and Ganoderma DNA observed at 3 d.
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Infection of oil palm can occur at any stage of its life-cycle and the stem fractures in severe disease progression Rees et al. Young palms usually die within months after the first symptoms are observed, whereas mature palms may withstand the infection for another years before dying Paterson, The first symptoms of infection are similar to drought conditions. Fully elongated but unopened spears are seen in the centre of the crown Corley and Tinker, This indicates that the stem or root system is already extensively damaged, thereby restricting water uptake, but this is not diagnostic for basal stem rot.
The lower leaves collapse in old palms and they hang downwards vertically from the point of attachment to the trunk and drooping of younger leaves follow which turn a pale olive-green or yellow and die back from the tip. The base of the stem blackens and later, gum may exude and the basidiomata of G.
The crown of the palm may then fall off or the trunk collapses. The peripheral tissues are hard and unaffected by rot, with the black fibres in this zone being normal. The majority of the stem tissue is yellow and disintegrates readily within the stem at the base. Mycelium can be found extended through the tissues. Roots are also found infected with the cortex being brown and decaying and the stele black. Large numbers of basidiomata may be formed with the early ones being small and rounded and the later ones being typical basidiomata.
Palms normally die within 6 to 12 months after the appearance of unexpanded spear leaves. Histopathological studies show that the fungus colonized the cortex, endodermis, pericycle, xylem, phloem and pith of the palm Rees et al. In older roots, the fungus may be observed as a whitish skin-like layer on the inner surface of the exodermis. As root tissues will be infected before foliar or stem lesion symptoms are observed, they are often found completely dead and colonized by many saprophytic micro-organisms.
Once the palm dies, basidiomata frequently appear along the entire trunk, indicative of a more rapid saprophytic colonization of the tissues. The currently used control strategies for basal stem rot BSR include physical, chemical and biological methods.
These are intended to a curtail the incidence of BSR after replanting and b increase the productive life of the infected oil palm. The extent to which they are effective is debatable. Physical control methods depend on accurate diagnostic methods, which are unavailable as mentioned, making control even more problematic.
Sanitation involves elimination measures such as clean clearing and windrowing. They intend to minimize the spread of the inoculum although they are expensive. The Indonesian government has issued numerous laws on land fires but these are poorly regulated as recent fires testify. The disease may be reduced by clearing old trees before they reach greatest susceptibility.
Infected palm trunks usually take 2 years for complete degradation. However, windrows often harbour pests, such as the Asiatic rhinoceros beetle Oryctes rhinoceros and rats, and may allow fungal pathogens to survive Paterson et al. Minimization of wounds to the palm is desirable as G. Sanderson et al. Infected palms were removed from the plantations, the trunk base and root ring were excavated to cm below ground, and the area was covered with soil to prevent further bracket formation.
In addition, removing basidiomata from diseased palms and painting them with carbolineum fungicidal paste Turner, to avoid spore dispersion was also suggested. Controlling BSR by means of surgery by the excision of the diseased part of the outer stem tissues and applying a protectant coating coal tar or thiram was used to treat the open surfaces to prevent further decay Turner, Mixed results occurred in the treated palms, which has led to a decline in the practice.
Curative surgery requires frequent repetitions, as infection often re-emerges if the lesions are not completely removed. In some estates in Sumatra, Indonesia, mounding has become routine practice for all infected palms over 15 years old, prolonging their economic life Hasan and Turner, The economic life of G.
Also, weakened boles are supported thus preventing them from being toppled by wind and further to stimulate the formation of new roots Turner, Soil mounding appears an effective treatment. Findings suggest that low molecular weight phenolic compounds can control the disease Surendran et al.
Fertilizers are also linked to increased climate change by releasing large quantities of nitrous oxide into the atmosphere Paterson and Lima, More field work is required based on these results. Biological control agents often suffer from lack of effectiveness in the field due to susceptibility to environmental conditions namely temperature, humidity, soil pH, etc. These have not provided a solution to BSR.
A large-scale nursery trial was conducted in Indonesia using more than 25 biological control agents and incidence was significantly lower in palms treated with T. This treatment was suggested to prolong the life of palms by up to years. Theoretically, biocontrol is an advance compared to other approaches and bio-fungicides are available in the market. However, the efficacy of the preparations in the field is a major concern and they have not cured BSR by any means.
It is worth considering the commercial products that are available. Biodegradation of oil palm debris for disease control. Once oil palm has become diseased and fallen over, managing the waste is a major issue. Enhanced biodegradation is a possible method to degrade the waste but requires more work to find a practical procedure Paterson et al. White rot hymenomycetes were utilized to antagonize Ganoderma and increase the rate of oil palm debris degradation Naidu et al.
Strains of Nocardiopsis , Streptomyces violaceorubidus and Streptomyces isolated from empty fruit bunches had enzymatic potential and antagonistic activity against Ganoderma Ting et al. However, these are not white rot fungi and will not degrade lignin as effectively as white rot fungi. Resistant planting materials. Breeding programmes now exploit genetic resources to provide resistance to diseases Rival and Jaligot, Genetic resistance was confirmed by Durand-Gasselin et al.
However, the genes for Ganoderma resistance have not been investigated. A transgenic approach is potentially promising but unlikely to provide an immediately commercially acceptable solution. There are few investigations where control methods have been tested on a large scale in plantations: these are likely the most suitable methods for general application.
Sundram et al. However, trials need extension to mature oil palms and not just seedlings. A field trial for Ganoderma control indicated that treatment with T. A large-scale trial showed that the disease incidence was lower in a field treated with the agents than in untreated fields Susanto et al.
A preparation should be available by now from this work that was proven to control the disease beyond any doubt, but this is not the case. Land preparation Land preparation procedures are based on the largely wrong assumption that infection occurs by mycelial spread from root to root and that the removal of stumps and large pieces of debris will eliminate viable residual inoculum from the field before planting of the next crop.
However, removal of debris may be an effective source of basidiospores. Such practices have been widely adopted throughout South-East Asia, to different degrees, dependent on BSR incidence in previous plantings, labour availability and the costs involved. More scientific studies are required to prove its worth. Clean clearing These methods are based on the concept of root to root infection of the disease which is now considered as less important than basidiospores primary and secondary infection Pilotti et al.
However, clean clearing will at least remove plant material from further colonization by the fungus hence decreasing basidiospore formation. Current procedures involve excision and removal of all remaining bole fragments by digging pits 1.
Cauterization by burning of the root-ends along the sides of the pits is also common. In areas with a high incidence of BSR, it is generally thought that all remaining fragments from the previous crop should be brought to the surface for subsequent removal.
However, as this is frequently regarded as too costly, and as open burning is now forbidden in Malaysia under the Clean Air Regulations Act of , a common practice is to shred all palm fragments. These can either be scattered over the whole field or stacked in rows and covered with a legume cover crop to facilitate decay and deter colonization of the palm debris from Oryctes.
Shredding oil palm tissues has been adopted in some areas in Malaysia but not in Sumatra Flood et al. The BSR levels may be influenced by being contiguous with peninsular Malaysia where the disease levels are high Paterson, b. Papua New Guinea has an important palm oil industry Corley and Tinker, The Philippines has an oil palm industry at a lower level than that of Thailand Corley and Tinker, BSR will be low as the plantations have not been established recently Woods, and distances between plantations will be high.
Equally, there are no reports of infection by BSR in the literature. Hence a low level of BSR can be expected. BSR of oil palms has been recorded widely throughout the tropics and is considered as a serious disease in Africa and South America. Infection of young palms has become a serious problem in Papua New Guinea Pilotti et al. The malady affects mature oil palms, young palms and seedlings in Malaysia and the fungus can reduce yields by ca.
Oil palms are frequently monocultures in South-East Asia on areas previously supporting other plantation crops such as rubber or coconuts, or may be planted on areas cleared from primary forest Paterson and Lima, Smallholder farmers also grow oil palms in mixed cropping systems with other perennials such as coconuts, coffee and cocoa.
Furthermore, infection tends to occur at a progressively earlier stage in the life of oil palms, and more frequently with each successive planting, such that widespread losses can occur in young plantings of less than 5 years.
Cases of BSR can be seen after only years in the field when replanting after coconut Ariffin et al. The future effect of the disease under climate change has been assessed by Paterson, a , b. The infection of oil palm by G.
Oil palm will be severely affected by climate change with the climate becoming increasingly unsuitable for growth of the palm particularly after making the palm more susceptible to BSR per se.
Detection and Control of Ganoderma boninense in Oil Palm Crop
Sarawak, a major producer in Malaysia, is also affected by this disease. Emergence of BSR in oil palm planted on peat throughout Sarawak is alarming as the soil type was previously regarded as non-conducive. Phylogenetic analysis indicated a single species, G. Information on evolutionary and demographic history for G. Sequence variations were analysed for population structure, phylogenetic and phylogeographic relationships.
List of symptoms / signs