The following text is an updated version of parts of the chapter "Towards Innovative Coconut Breeding Programs", by Dharshani Bandupriya, Chandrika Perera, Messias Pereira and Roland Bourdeix, published in the 2020 Springer book: Coconut Biotechnology: Towards the Sustainability of the ‘Tree of Life', edited by Steve Adkins, Mike Foale, Roland Bourdeix, Quang Nguyen, and Julianne Biddle. The text was reviewed and approved in Côte d'Ivoire by the CNRA coconut program team (in particular Dr J. L. Konan, CNRA Scientific Director, Dr N. Hala, Coconut Program Manager and Dr K. Allou, Entomo-pathologist).
A successful clonal propagation method will pave the way for the enhancement of the coconut industry by making available planting material, certified disease-free, to meet the large demand, providing that the genetic quality and stability of the clones can be assured. Moreover, the production of coconut clones may have a direct positive impact on the conservation of germplasm.
During the last decades, plumule explants have been preferred by lab researchers due to their better response compared to other explants, but they are not at all the most convenient for breeders. The production of clones of palms with unknown performance due to the cross pollination in coconut is the major disadvantage of using plumule explants. In fact, it was not possible to reproduce a genotype, but only the progeny of this genotype, and this is indeed a major constraint for reproducing the best hybrids.More recently, in 2021, a novel micropropagation method was discovered, based on axillary shoot formation. This innovative micropropagation method may enable the production of disease-free, True to type high quality in vitro plantlets. As it allows to reproduce genotypes and not only the progeny of a genotype, this new technique, if confirmed, may solve the worldwide scarcity of coconut planting material.
It is essential to avoid falling for the mistake of applying sophisticated laboratory methods to questionable biological materials, whose performance and characteristics are not appropriately evaluated in the field. |
For instance, it is not enough to identify, in farmers' fields or in poorly managed heterogeneous experiments, a few coconut palms that have apparent positive characteristics for cloning. This will not revolutionize coconut cultivation and will not satisfy farmers.
The analysis presented in our 2020 Springer chapter shows that most conventional coconut breeding programs are currently facing both material and methodological impasses. The budgets and experimental areas allocated to these programs often remain insufficient to reach substantial genetic progress. The improvement of hybrids is neglected and often methodologically limited.
There is a great risk of having dozens of researchers absolutely convinced that they have the best clones in the world, when they only chose trees that had a favorable phenotype, without resorting to reliable genetic improvement techniques: and there is a great risk that this situation will cause great confusion for users, and in particular farmers.
The best coconut clones will be found in field experiments specifically designed for genetic improvement and/or clonal selection: after a first choice of the best progenies, the best trees within these progenies will have to be used for true-to-type clonal propagation. |
Currently, many breeding programs devoted to coconut hybrids are limited to testing new crosses between traditional coconut varieties. Breeders collect new traditional varieties and introduce them into their collection; then they create and test new hybrids, generally by favouring Dwarf ×Tall types, and more recently Dwarf × Dwarf types. 
Individual palms chosen in parental varieties are selected on their phenotype and not on the value of their individual progenies. This type of methodology will not continue to maintain substantial genetic progress. Geraldo Santos, a famous former coconut breeder, already depicted such situation in the 2000’s: “in the Philippines, we tested more than 100 hybrids between Tall and Dwarf types, now this is OK, we do not want to test more!” (R. Bourdeix, personal communication). If breeders continue to use the same method again and again, the results will be limited. Yields will cap.
Hybrids which are considered ‘best’ between traditional varieties have been sometimes improved using the individual combining ability testing method, which takes advantage of the genetic variability within Tall varieties.
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| Example of improvement of a Dwarf x Tall Hybrid |
This can be explained using the following example: PB113 is hybrid developed by crossing the CRD (Cameroon Red Dwarf) and a selected population of RIT (Rennell Island Tall). Their excellent performance has been further enhanced. Forty-five RIT parent palms have been individually crossed with CRD. The progenies obtained are therefore, half-sib families each from one RIT as male and several CRD as female. In the absence of a secure cloning method that does not destroy the sampled palms; the individually tested male parents have been conserved and multiplied by selfing. The best self-families, each constituted of about 100 are conserved as pollen donors for seednut production. The results of these experiments show that selecting the best families give 15 to 30% genetic progress on yields (Bourdeix et al. 1989). It is to be noted that these experiments were mainly planted in Côte d'Ivoire before 1990. Vanuatu also planted a few experiments but has not yet released their results to farmers.
The best half-sib families located in these experiments are among the progenies where the best individuals and clones could be chosen. This choice would benefit from one more breeding generation. In Côte d’Ivoire, this selection was not done, and experiments are now endangered by the probable expropriation of the “Marc Delorme research centre”, but also by aging, lack of maintenance or the cutting down of old experiments. At present, we can consider that at least 20% of the coconut palms which could give the best clones in the world are already dead.
As far as we know, the improvement of the best hybrids using progeny tests was only conducted in Côte d'Ivoire and Vanuatu. Fortunately, all the data of these experiments have been carrefully conserved in the CIRAD software "Coconut Data Management". So, even if some of these experiments are now more than 30 years old, it remains possible to conduct analysis on the old data (generally production from 4 to 12 years) and to select the best candidates for cloning. Molecular techniques will also help to select the best clones.
It is in these experiments in Côte d'Ivoire and Vanuatu, and nowhere else, that the best clones will be detected. These clones will produce 15-20% more than those selected in first generation experiments available in other countries. But the trees from those old experiments are dying. It is therefore urgent and crucial to develop a research program to safeguard this unique genetic heritage. |
©R. Bourdeix, 2022, section CAGC, copying is not allowed.
