Oil palm natural diversity and the potential for yield improvement

Abstract

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.

Keywords: E. guineensis; E. oleifera; breeding; germplasm; hybrid; oil palm.

FIGURE 1

E. guineensis and E. oleifera. (A) Commercial African tenera oil palm from a cross dura Deli × pisifera Nigeria. The tree is 5-years-old and has nigrescens fruit type (inset). (B) 26-years-old plantation of tenera palms (Deli × Ghana). Trees are 7–8 meters tall. (C) Fruit bunch harvest. A worker is using a knife to cut off bunches from a tree on a plantation shown in (B). Bunch ripeness is assessed by the presence on the ground of the shed-off fruits. (D) E. oleifera. The wild tree that is more than 30-years-old (Manicoré, Amazonas, Brazil). (E) Walking palm. The same tree as in (D) photographed at different angle to illustrate procumbent trunk that is outlined by the dotted line. (F) African oil palm male inflorescences. This individual has particularly long male inflorescence stalks that are pointed with arrows. (G) Fruit bunch stalk. The 3-months-old fruit bunch of the American oil palm is shown. Bar indicates short stalk. (H) Collection of E. oleifera bunch. Harvesting oil palm requires skilled workers, even when trees are not very tall. (I) Thickness of the bunch stalk. The cut-off bunch from a tree in (H). Cutting through the bunch stalk (orange arrow) composed of a very fibrous tissue, requires physical strength.

FIGURE 2

E. oleifera × E. guineensis interspecific hybrids at EMBRAPA breeding station Rio Urubu (Amazonas, Brazil). (A) Controlled pollination. Worker is removing the spathe on elite E. oleifera tree that is three meters tall. He wears safety gear to climb the tree, protective mask and gloves. In commercial seed production, female inflorescences are bagged 1 week before anthesis. (B) Bunch ripening. Three bunches at different times after pollination are visible. As fruit mature, the fruits change color from green to orange. The youngest female inflorescences were not used in pollination, those bunches are still enclosed in spathe, which is an E. oleifera species-specific characteristic. (C) F1 interspecific hybrid on commercial plantation. Tree is 4 years old. It has about twice shorter stem than African oil palm trees of the same age. Orange mature bunches are easily spotted within the tree crown. (D) Parthenocarpic fruits in mature bunch of the F1 interspecific hybrid. Insert: a few fruits were transversely cut. The fruit to the right has normal seed. White colored endosperm tissue of the kernel is surrounded by the black endocarp, mesocarp is orange. Parthenocarpic fruits have residual black endocarp and no kernel. (E) Female inflorescence of F1 hybrid at anthesis. Inflorescence is still enclosed in spathe, which is similar to the parent E. oleifera. (F) Female flowers. The same inflorescence as in (E). Spathe was removed to show female flowers at anthesis. Three-lobed flower stigmas are yellowish in color and receptive for pollen. (G) Male inflorescence of F1 hybrid at anthesis. The overall morphology and flower identity are normal. (H) Andromorphic inflorescences. This 15-years-old tree developed five fully andromorphic inflorescences pointed with blue arrows and a single male inflorescence (behind the leaf rachises to the right). Orange arrow points a fruit bunch. (I) Partial andromorphy. Individual andromorphic inflorescence can show different proportions of male flowers (orange arrow) and female flowers (blue arrow). (J) Fruitlets from andromorphic inflorescence. Some fruitlets abort after anthesis, died dry flower pistils are black (orange arrow), other develop parthenocarpically (blue arrow). Andromorphic inflorescences in (H) are full of developing fruitlets.