Molecular Biology

ASD Molecular Biology Program

Introduction

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ASD Costa Rica (Agricultural Services & Development) is a company that develops technology for oil palm cultivation. ASD’s certified seed and clone varieties for planting at high densities are sold in the tropical and intertropical regions of Asia, Africa and America.

ASD has more than 450 hectares planted with field trials in the southern region of Costa Rica, where there is one of the most diverse collections of oil palm germplasm in the world. The first introductions of germplasm were made in 1928; however, the genetic improvement program was intensified and consolidated by 1975. Some important achievements of this program have been the development of six commercial varieties for planting under normal conditions for cultivation, two varieties for areas with extreme conditions, three high density varieties and one exceptional OxG hybrid.

Historically, the ASD oil palm breeding program has used classical breeding methods, which require large areas for field experiments and long periods of time to evaluate the behavior of each new generation of palms. Nevertheless, remarkable advances in molecular biology allow the identification of genes and their functions; which provide an opportunity to make genetic improvement more effective and faster.

The ASD molecular biology program began in 2006, with the objective of using and developing molecular biology tools such as genetic markers and sequencing, to assist the breeding program. The idea is to complement and, if possible, eventually substitute genotypic evaluation and selection methods. The different projects that ASD has undertaken to develop new varieties with the help of molecular biology are described below.

"Compact Gene" to increasing planting density

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The term 'compact palm' has been used to characterize palms that have slow trunk growth rates and short leaves. These palms can be planted at higher density and allow prolonging the economic life of the plantation.

In 1966, ASD identified a palm from a hybrid (E. oleifera x E. guineensis) naturally pollinated with E. guineensis pollen (open pollination). This palm (E. oleifera x E. guineensis) x E. guineensis, with short trunk and leaves and a composition of ¾ E. guineensis genes and ¼ E. oleifera genes, was called the original compact palm (OCP). It is believed that the OCP’s compact trait was acquired from the E. oleifera father.

This project aims to associate genetic markers with quantitative trait loci (QTLs) such as compact growth through the development of a linkage map. This identification will allow the manipulation of this character within ASD germplasm. With the use of compact varieties and/or clones, oil productivity per hectare could be increased by 30% or more.

Identification of dura, tenera and pisifera genes

In oil palm there are three types of fruits: dura, tenera and pisifera. These differ in the thickness of the shell (endocarp) and in mesocarp content. Dura type fruits have a thick shell, thin mesocarp and relatively little oil. Pisifera fruits do not have a shell and most palms with this characteristic are naturally sterile, which is why they are not economically important. Tenera fruits have a thin shell and a thick mesocarp with high oil content (greater than 25%).

The endocarp thickness trait is governed by a pair of genes with intermediate inheritance. The identification of dura, tenera and pisifera palms with genetic markers in the nursery stage (without having to wait several years to verify the type of fruit) will undoubtedly save time and reduce research costs.

'Virescens' gene to improving harvest efficiency

A change in color is associated with the maturity of oil palm fruits. Therefore, this color change is one of the indicators normally used to identify ripe bunches with the maximum oil content. However, this indicator is not always clear in bunches with nigrescens fruits (black when they are immature), where the color change that indicates optimum ripening may be very tentative, which leads to harvesting bunches that have not accumulated the maximum oil content.

One alternative for improving harvesting efficiency is the creation of varieties with virescens fruits, which are bright green when they are immature and change to bright orange when they ripe; this makes them easily recognizable and helps avoid harvesting unripe bunches.

Low dehiscence in bunches to reduce crop losses

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Oil palm fruits naturally detach from the bunch when they ripen. Because the ripening process of different fruits is gradual, it may take more than 10 days from when the first fruits are released until the last ones are ripe, making it difficult to harvest bunches with an optimum degree of ripening. In addition, due to dehiscence, loose fruits that fall to the ground must be collected by hand, which increases harvesting costs significantly.

It is estimated that if bunches ripen without fruit detachment, oil production could increase by 20-25%. Fortunately, there are mutant palms that have bunches without abscission, where ripe fruits remain attached to the bunch. The genetics of this trait are not yet known; however, we are already working on this through particular crossings.

The problem that a ripe bunch without fruit detachment would present is that its ripening could not be judged by the presence of fruits on the ground. However, this can easily be solved with the simultaneous introduction of the virescens gene described above. ASD has identified palms and families that have bunches with low or no dehiscence of ripe fruits (dura bunches). These palms could be cloned or used to transmit the low dehiscence trait to their progeny.

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Legitimacy of clones

The use of clones in commercial plantations is a viable reality due to advances in tissue culture technology, which allows reproducing thousands of ramets. Genetically, the clones must be identical copies of the tissue donor palms (ortets), in order to reproduce their genetic potential. The verification that the clones possess the same genetic load of the ortet (genetic fingerprint) is an important guarantee in the commercialization of the clones.

Modification of oil chemical composition

Palm oil has a relatively high content of saturated fatty acids, mainly palmitic acid (45-58%). Altering the composition of the oil to make it more liquid and increase its oleic acid content would improve the value of this product. This objective can be achieved by identifying particular molecular markers in individuals with high unsaturated oil content in populations of Elaeis guineensis, Elaeis oleifera and their hybrids, to produce clones or varieties with high olein content. Eventually the composition of the oil could be changed with the help of genetic engineering.

Genetic associations between different sources of germplasm

Knowledge of genetic distances between germplasm of different origins can be useful in associating genetic materials of similar origin and manipulating them as a single population, in order to reduce the amount of materials to be evaluated in the process of developing and improving new varieties. In addition, maintenance and data collection costs would be reduced by managing fewer populations.