The ongoing expansion of oil palm plantations in the humid tropics, especially in Southeast Asia, is generating considerable concern and debate. Amid industry and environmental campaigners' claims, it can be hard to perceive reality. Is oil palm a valuable route to sustainable development or a costly road to environmental ruin? Inevitably, any answer depends on many choices. But do decision makers have the information they require to avoid pitfalls and make the best decisions? This review examines what we know and what we don't know about oil palm developments. Our sources include academic publications and ‘grey' literature, along with expert consultations. Some facts are indisputable: among these are that oil palm is highly productive and commercially profitable at large scales, and that palm oil demand is rising. Implementing oil palm developments involves many tradeoffs. Oil palm's considerable profitability offers wealth and development where wealth and development are needed—but also threatens traditional livelihoods. It offers a route out of poverty, while also making people vulnerable to exploitation, misinformation and market instabilities. It threatens rich biological diversity—while also offering the finance needed to protect forest. It offers a renewable source of fuel, but also threatens to increase global carbon emissions. We remain uncertain of the full implications of current choices. How can local, regional and international benefits be increased while costs are minimised? While much important information is available, it is often open to question or hard to generalise. We conclude this review with a list of pressing questions requiring further investigation. Credible, unbiased research on these issues will move the discussion and practice forward.

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The impacts and opportunities of oil palm in Southeast Asia: What do we know and what do we need to know?

African oil palm has the highest productivity amongst cultivated oleaginous crops. Species can constitute a single crop capable to fulfill the growing global demand for vegetable oils, which is estimated to reach 240 million tons by 2050. Two types of vegetable oil are extracted from the palm fruit on commercial scale. The crude palm oil and kernel palm oil have different fatty acid profiles, which increases versatility of the crop in industrial applications. Plantations of the current varieties have economic life-span around 25-30 years and produce fruits around the year. Thus, predictable annual palm oil supply enables marketing plans and adjustments in line with the economic forecasts. Oil palm cultivation is one of the most profitable land uses in the humid tropics. Oil palm fruits are the richest plant source of pro-vitamin A and vitamin E. Hence, crop both alleviates poverty, and could provide a simple practical solution to eliminate global pro-vitamin A deficiency. Oil palm is a perennial, evergreen tree adapted to cultivation in biodiversity rich equatorial land areas. The growing demand for the palm oil threatens the future of the rain forests and has a large negative impact on biodiversity. Plant science faces three major challenges to make oil palm the key element of building the future sustainable world. The global average yield of 3.5 tons of oil per hectare (t) should be raised to the full yield potential estimated at 11-18t. The tree architecture must be changed to lower labor intensity and improve mechanization of the harvest. Oil composition should be tailored to the evolving needs of the food, oleochemical and fuel industries. The release of the oil palm reference genome sequence in 2013 was the key step toward this goal. The molecular bases of agronomically important traits can be and are beginning to be understood at the single base pair resolution, enabling gene-centered breeding and engineering of this remarkable crop.

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Oil palm natural diversity and the potential for yield improvement

The oil palm, an economically important tree, has been one of the world’s major sources of edible oil and a significant precursor of biodiesel fuel. Unfortunately, it now faces the threat of a devastating disease. Many researchers have identified Ganoderma boninense as the major pathogen that affects the oil palm tree and eventually kills it. But identification of the pathogen is just the first step. No single method has yet been able to halt the continuing spread of the disease. This paper discusses the modes of infection and transmission of Ganoderma boninense and suggests techniques for its early detection. Additionally, the paper proposes some possible ways of controlling the disease. Such measures, if implemented, could contribute significantly to the sustainability of the palm oil industry in South East Asia.

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Detection and control of Ganoderma boninense: strategies and perspectives

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 thick-walled 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

https://bsppjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3059.2009.02100.x

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

In recent years, the oil palm sector has witnessed a period of historically high prices with buoyant global demand and high levels of production driven largely by economic development in major Asian countries such as India and China. However, the oil palm sector is also confronted by many important challenges that require attention. Such challenges include fragmentation of the industry, stagnating yields, and an image problem that is largely due to the conversion of tropical rainforest and peatlands in a few regions in South-east Asia. The biological and managerial tools to surmount these challenges already exist but need more focussed application and political support. Potentially groundbreaking biological tools include the new molecular breeding technologies, such as those made possible by the recent publication of the oil palm genome sequence (Singh et al., 2013a, b). Two key RD and • higher mesocarp oleic acid composition – preferably over 65% w/w. The more focussed use of new and traditional technologies can also help to confront pest and disease problems, to redesign of crop architecture, and to facilitate yield and harvesting efficiency. In the mediumterm future, we can look forward to a considerable geographical extension of oil palm cultivation in a broad zone across the tropics of Africa, Asia and the Americas. If these and other measures can be taken, increased palm oil output could more than meet the highest projections for future vegetable oil requirements while minimising adverse environmental consequences. Improved oil palm varieties could also considerably increase the global market share for this highly productive tropical crop at the expense of some of the less efficient temperate oilseed crops.

THE FUTURE OF OiL PaLM as a MaJOR GLOBaL CROP: OPPORTUniTiEs anD CHaLLEnGEs

Ganoderma boninense causes severe losses to oil palm in South East Asia. The disease typically manifests itself as basal stem rot, but there remains controversy over the route of infection and source of inoculum. Using isolates differing in aggressiveness, infection via roots was confirmed; it was also shown that large inoculum provided as Ganoderma-infested palm- or rubber-wood blocks (12 × 6 × 6 cm) is necessary for soil infection of seedlings after 6–8 months. Smaller blocks (3 × 3 × 3 cm) produced rapid (≤ 3 months) infection of roots and lower stem when physically attached to roots. Therefore fragmentation of infested palm wood from a felled, mature plantation before subsequent replanting may provide inoculum. Failure of G. boninense to grow through non-sterile soil or organic debris from frond bases, suggests it is a poor competitor and that roots must contact inoculum directly. Severe disease occurred after 8 months on inoculated seedlings under shade, but not on seedlings exposed to sun. Soil temperatures in sunlight frequently rose above 40°C and reached 45°C, whereas in shade they never exceeded 32°C. Ganoderma boninense is probably inhibited in exposed soil since optimal growth in vitro was 25–30°C, and there was no recovery from 45°C. Soil temperature may explain why symptoms often first appear in mature plantations when canopy formation creates shade. Infection is not peculiar to senescing palms but can occur throughout the growth cycle.

Effects of inoculum potential, shading and soil temperature on root infection of oil palm seedlings by the basal stem rot pathogen Ganoderma boninense

Basidiospores are implicated in the distribution and genetic diversity of Ganoderma boninense, cause of basal stem rot (BSR) and upper stem rot (USR) of oil palm (Elaeis guineensis). Measurement of aerial basidiospores within plantations in Sumatra showed continuous and high production over 24 h (range c. 2–11 000 spores m−3) with maximum release during early evening. Basidiospores applied to cut surfaces of fronds, peduncles and stems germinated in situ. Equivalent, extensive wounds are created during plantation harvesting and management and represent potential sites for formation of infective heterokaryons following mating of haploid basidiospore germlings. Use of spore-sized micro-beads showed that basidiospores could be pulled up to 10 cm into severed xylem vessels, where they are relatively protected from dehydration, UV irradiation and competing microflora. Diversity of isolates from five locations on two plantations was assessed by RAMS fingerprinting. Isolates from within individual palms with USR were identical and represent single infections, but different USR infections had unique band patterns and revealed separate infections. Some BSR-affected trees contained more than one isolate, and thus had multiple infections. There was one example of adjacent BSR palms with the same isolate, indicating vegetative spread, but there were no identical genets from BSR infections and adjacent fallen palms. Isolate diversity was as great within a plantation as between plantations. It is evident that basidiospores play a major role in spread and genetic variability of G. boninense. Evidence for direct basidiospore infection via cut fronds, indirectly through roots via colonized debris and less frequently, infection by vegetative, clonal spread is considered.

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Ganoderma boninense basidiospores in oil palm plantations: evaluation of their possible role in stem rots of Elaeis guineensis

The internally transcribed spacer (ITS) regions of the ribosomal RNA (rRNA) gene cluster of 161 isolates of Phytophthora species involved in pod rot, stem canker and leaf blight of cocoa were analysed to determine inter- and intraspecific variation in this disease complex. The species P. palmivora , P. megakarya , P. capsici , P. citrophthora and P. nicotianae could all be clearly distinguished by PCR amplification of the ITS region followed by restriction analysis with Hae III, Hinf I, Pvu II and Alu I. This method provided a relatively rapid identification procedure for these species, and was able to distinguish isolates that had previously been misidentified by morphological methods. Sequence analysis showed that the four main cocoa-associated species formed two distinct groups, one comprising P. capsici and P. citrophthora , and the other P. palmivora and P. megakarya . Detailed sequence analysis and comparison with published literature suggested that P. capsici isolates from cocoa may be closely related to P. tropicalis , a species recently described from Cyclamen and Dianthus .

http://orton.catie.ac.cr/repdoc/A4822i/A4822i.pdf

Molecular analysis of the major Phytophthora species on cocoa

Difficulties in the accurate identification of the Phytophthora species responsible for black pod disease of cocoa continue to hamper effective disease control. A re-evaluation of morphological characters (Brasier & Griffin, 1979) and a detailed morphometric analysis of 161 Phytophthora isolates largely associated with black pod disease of cocoa from 17 countries worldwide have shown considerable inter- and intraspecific variation. Stable and more reliable parameters for the identification of the species responsible for the disease have been determined. Colony characteristics such as pattern and growth rate on V8 agar are reasonably characteristic for the cocoa Phytophthora species, and can be used to make preliminary identification to species level. Significant sporangial character variation was found within isolates of species from the same and different sources, highlighting the difficulties in making accurate identification on the basis of raw morphological data. Pedicel length was found to be the most consistent species-linked sporangial characteristic. Cluster plots of length/breadth ratios of sporangia versus reciprocals of sporangial pedicel length clearly separated all isolates into distinct species groups (P. capsici, P. citrophthora, P. palmivora and P. megakarya) and can be used reliably to identify accurately those pathogens involved in black pod disease outbreaks.

J. Flood

Papers

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

Effects of inoculum potential, shading and soil temperature on root infection of oil palm seedlings by the basal stem rot pathogen Ganoderma boninense

Ganoderma boninense basidiospores in oil palm plantations: evaluation of their possible role in stem rots of Elaeis guineensis

Molecular analysis of the major Phytophthora species on cocoa

Inter- and intraspecific morphometric variation and characterization of Phytophthora isolates from cocoa