Advanced methods for improving local tall-type populations

By R. Bourdeix, 2018

Nothing can replace a well-designed, regular and sustainable coconut breeding program conducted by well-trained professionals. Very few countries have succeeded in creating and maintaining such a program, which requires the yearly planting of at least ten hectares of fields breeding experiments.

From the breeder’s point of view, there are three variants of mass selection, based on the reproductive system used - mass selection using open pollination, intercrossing or selfing (Bourdeix, 1988). Mass selection using open pollination has been practiced the most but is efficient only on a very long term (see dedicated section). Mass selection using intercrossing appears more effective, as it allows for a strict selection of pollinators while retaining the potential for large seednut production. This method was applyed in Vanuatu. Mass selection using self-Pollination induces an inbreeding depression  and is not recommended for seednut production.

Mass selection using controlled pollination and crossing between best palms
This method was applied with success in Vanuatu. Beginning with two Vanuatu Tall populations collected near the Saraoutou research centre, four mass selection cycles by open pollination or intercrossing were conducted from 1962 to 2002 (Labouisse et al., 2004). This programme resulted in improved Vanuatu Tall population that is now widely distributed to farmers. The main criterion of selection was copra weight per fruit. Because of the strong negative correlation between the number and weight of fruit (Bourdeix, 1988), there was no increase in the number of fruit per palm over the different generations, rather a slight decrease was observed.

Mass selection using self-Pollination
In the case of Tall-type coconut palms, several studies have shown that a single generation of selfing induces an inbreeding depression  and usually reduces the yield of fruits from 20 to 30%. Choosing best palms and selfing them will give a progeny with an average yield decline of 15 to 30% when compared to parent palms, without appreciably increasing production homogeneity. So this method is not recommended for seednut production.

Within-population selection based on progeny test
As in the case of mass selection, the methods described hereunder have a common denominator (i.e., the selected population initially was limited to only one local Tall coconut variety). All the classical methods based on within-population breeding can be applied to the coconut palm, although the long generation period and the low multiplication rate are strong limiting factors especially for an economically viable seednuts production system.
In 1967, Liyanage published a study dealing with the analysis of the open pollinated progenies of 104 Sri Lanka Tall. The low number of each progeny (nine half-sibs) seems insufficient to safeguard against divergence due to sampling and environmental effects. However, this study made it possible to estimate the effect of a selection based on the open pollinated progenies. The six best families among the 104 exhibited 32% higher yield level than the average. This genetic gain, although it might have been overestimated, could be compared to the 14 % progress obtained by mass selection. This study underlines another limit of mass selection (i.e., progeny tests are indispensable in evaluating the effectiveness of this method). Once these tests have been conducted, it is much better to select the parents on the basis of the progeny value than on the basis of their phenotypic value. The selection of half-sib families (HS) is therefore more effective than the mass selection method. 
A pragmatic coconut breeder could ask the following question: “Why focus on a within variety breeding method when the hybrid vigour between varieties gives an opportunity of immediate and appreciable genetic progress?” Nevertheless, the within-population breeding strategy is sometimes fully justified. For instance, in the Vanuatu archipelago, only one local variety is resistant to a lethal disease. In many countries, there is a cultural co-evolution between farmers and their traditional varieties. Farmers do not want to loose their traditional varieties even if most of them also plant and try some new coconut hybrids. However, these precious Tall-type varieties must also be improved using a participatory approach so that farmers’ preferences will be taken into account during the selection process.

Bourdeix, R. (1988). Efficacité de la sélection massale sur les composantes du rendement chez le cocotier (Effectiveness of mass selection based on yield components in coconut). Oléagineux (France). 43, 7: 283-295.
Bourdeix R. (1999). Coconut selection and breeding. Pp. 117-196 in Modern Coconut Management (J.G. Ohler Ed). Intermediate Technology Publications, FAO, Universeteit Leiden.
Labouisse J.P., Sileye, T., Morin, J.P., Hamelin, C., Baudouin, L., Bourdeix, R. and Rouzière, A. (2004). Coconut (Cocos nucifera L.) genetic improvement in Vanuatu: Overview of research achievements from 1962 to 2002. OCL 11. (4): 354-61.
Labouisse J.P., Sileye, T., Morin, J.P., Hamelin, C., Baudouin, L., Bourdeix, R. and Rouzière, A. (2004). Coconut (Cocos nucifera L.) genetic improvement in Vanuatu: Overview of research achievements from 1962 to 2002. OCL 11. (4): 354-61.