Norbert Billotte

Geographic and genetic structure of African oil palm diversity suggests new approaches to breeding.

Since the 1960s, there has been very little diversification of oil palm (Elaeis guineensis) seed production, with mainly Deli × La Mé and Deli × Congo type crosses. The Deli origin, which was introduced from Africa into Indonesia in 1848, is unavoidable in breeding. In order to understand the complementarity between the Africa and “Asia” origins, and to diversify the genetic base of oil palm production, the structure of the genetic resources involved in the history of oil palm breeding in relation to African germplasm including subspontaneous populations needs to be understood. In this study, 318 individuals from 26 origins and eight countries were analysed with 14 microsatellite loci. Descriptive and Bayesian analyses of oil palm genetic diversity (Principal Coordinates Analysis, Neighbour-Joining Tree and Structure software) revealed two original groups which reflected the discontinuity of African species at the Dahomey Gap, West Africa (Group I) on the one hand, and “Benin-Nigeria-Cameroon-Congo-Angola” (Group II) on the other hand. The Deli group (Group III), derived from group II, is the result of artificial selection (mass selection). The genetic structuring revealed showed the positive contribution of the within-population mass selection practiced in the Deli population, and explains the success of Deli × La Mé and Deli × Congo crosses. A selection strategy is proposed, based on the yet-to-be-exploited complementarity that exists between the two African genetic groups and on within-group improvement. We suggest (Deli × Group II) × Group I crosses, so that group II benefits from the quality of the Deli origin.

Genetic isolation of Cape Verde Island Phoenix atlantica (Arecaceae) revealed by microsatellite markers.

Increasing human pressure on the environment in the isolated Macaronesian island group of Cape Verde is threatening many endemic species with extinction. The status of Phoenix atlantica, the Cape Verde Island date palm, is one of the unresolved taxonomic issues not only of the archipelago’s flora but also in the genus Phoenix. We applied 15 nuclear microsatellite markers and one chloroplast minisatellite marker to individuals of Phoenix from the Cape Verde Islands, P. dactylifera, P. canariensis and P. sylvestris, in order to assess the taxonomic position of P. atlantica within the genus. Our analysis showed that P. atlantica is clearly distinct from its close relatives and that its closest relative is likely to be its nearest geographical neighbour, P. dactylifera. Comparable levels of genetic diversity were found in insular P. atlantica and continental P. dactylifera despite the large difference in geographic range size. Our findings highlight the importance of conserving the relatively fragmented and isolated populations of P. atlantica as one of only␣two endemic trees on the islands and emphasise the need for further studies into its evolution and relationship with P. dactylifera.

Close Genetic Proximity Between Cultivated and Wild Bactris gasipaes Kunth Revealed by Microsatellite Markers in Western Ecuador

Bactris gasipaes Kunth (peach palm or Pejibaye) is the only domesticated palm of the Neotropics. The genetic relationships between the crop and its wild relatives are still unclear. We undertook field and laboratory work in order to describe differentiation and relationships between the wild and cultivated populations of the species in Western Ecuador, and their possible interactions. A volumetric study was undertaken on the fruits of both populations, as well as a population genetic analysis in order to clarify these relationships. Fruits from cultivated plants collected in the region of sympatry of wild and cultivated plants in North-West Ecuador showed intermediate volumes between those of reference samples for the wild and cultivated plants in allopatry. Using 8 microsatellite loci, we assessed 83 wild and cultivated individuals from Western Ecuador and cultivated plants from Amazonia and Central America as a reference for the cultivated form. We detected high polymorphism in the wild and cultivated samples and low, but significant level of genetic differentiation between wild and cultivated populations. The cultivated population in North-Western Ecuador showed close genetic proximity with the sympatric wild population, consistent with the volumetric study. These results have implications for hypotheses on evolution of this crop and for strategies of genetic conservation of the wild forms.

Genetic Architecture of Palm Oil Fatty Acid Composition in Cultivated Oil Palm (Elaeis guineensis Jacq.) Compared to Its Wild Relative E. oleifera (H.B.K) Cortés

We searched for quantitative trait loci (QTL) associated with the palm oil fatty acid composition of mature fruits of the oil palm E. guineensis Jacq. in comparison with its wild relative E. oleifera (H.B.K) Cortés. The oil palm cross LM2T x DA10D between two heterozygous parents was considered in our experiment as an intraspecific representative of E. guineensis. Its QTLs were compared to QTLs published for the same traits in an interspecific Elaeis pseudo-backcross used as an indirect representative of E. oleifera. Few correlations were found in E. guineensis between pulp fatty acid proportions and yield traits, allowing for the rather independent selection of both types of traits. Sixteen QTLs affecting palm oil fatty acid proportions and iodine value were identified in oil palm. The phenotypic variation explained by the detected QTLs was low to medium in E. guineensis, ranging between 10% and 36%. The explained cumulative variation was 29% for palmitic acid C16:0 (one QTL), 68% for stearic acid C18:0 (two QTLs), 50% for oleic acid C18:1 (three QTLs), 25% for linoleic acid C18:2 (one QTL), and 40% (two QTLs) for the iodine value. Good marker co-linearity was observed between the intraspecific and interspecific Simple Sequence Repeat (SSR) linkage maps. Specific QTL regions for several traits were found in each mapping population. Our comparative QTL results in both E. guineensis and interspecific materials strongly suggest that, apart from two common QTL zones, there are two specific QTL regions with major effects, which might be one in E. guineensis, the other in E. oleifera, which are independent of each other and harbor QTLs for several traits, indicating either pleiotropic effects or linkage. Using QTL maps connected by highly transferable SSR markers, our study established a good basis to decipher in the future such hypothesis at the Elaeis genus level.

QTL analysis of fruit components in the progeny of a Rennell Island Tall coconut (Cocos nucifera L.) individual

We investigated the genetic factors controlling fruit components in coconut by performing QTL analyses for fruit component weights and ratios in a segregating progeny of a Rennell Island Tall genotype. The underlying linkage map of this population was already established in a previous study, as well as QTL analyses for fruit production, which were used to complement our results. The addition of 53 new markers (mainly SSRs) led to minor amendments in the map. A total of 52 putative QTLs were identified for the 11 traits under study. Thirty-four of them were grouped in six small clusters, which probably correspond to single pleiotropic genes. Some additional QTLs located apart from these clusters also had relatively large effects on the individual traits. The QTLs for fruit component weight, endosperm humidity and fruit production were found at different locations in the genome, suggesting that efficient marker-assisted selection for yield can be achieved by selecting QTLs for the individual components. The detected QTLs descend from a genotype belonging to the “Pacific” coconut group. Based on the known molecular and phenotypic differences between “Pacific” and “Indo-Atlantic” coconuts, we suggest that a large fraction of coconut genetic diversity is still to be investigated by studying populations derived from crosses between these groups.

Genetic diversity of the world’s largest oil palm ( Elaeis guineensis Jacq.) field genebank accessions using microsatellite markers

The extent of genetic diversity among 494 oil palms from 49 populations (representing ten African countries, three breeding materials, and one semi-wild material) were assessed using 16 SSR markers. The genetic diversity was high with a total of 209 alleles detected accounting for an average of 13.1 alleles per locus and a mean expected heterozygosity of 0.644. The average genetic distance among accessions was 0.769, varying from 0.000 to 1.000. Both principal coordinates analysis and neighbor joining tree, confirmed by structure analysis, clustered the entire collections into three groups: the Extreme West Africa (EWA) group (collections from Senegal, Guinea, and Sierra Leone), the West, Central, and East Africa (WCEA) group (collections from Ghana, Nigeria, Cameroon, Zaire, Angola, Tanzania, Bahia, the semi-wild material and the two Deli breeding materials) and the Madagascar group (collections uniquely from Madagascar). Madagascar populations were found to be genetically distinct from all other African populations. The influence of human and environmental factors might have played a major role in grouping the African natural oil palm into three different groups as well as in the formation of a transition zone (formed by Ghana and Côte d’Ivoire). Further analysis of genetic structure revealed Deli materials as a distinct population within the WCEA group. Given the fact that accessions were exchanged between the EWA and WCEA groups, intra- and inter-group combinations for breeding should be based mainly on the genetic distance between accessions to increase yield and heterosis.

Cuticular wax composition in Cocos nucifera L.: physicochemical analysis of wax components and mapping of their QTLs onto the coconut molecular linkage map.

Cuticular waxes were extracted from the leaves of a coconut mapping population generated by the controlled cross of an East African Tall and a Rennell Island Tall genotype for the construction of molecular linkage maps. The wax composition was analyzed by capillary gas chromatography/mass spectrometry, and for eight of the wax compounds, their absolute and relative amounts were determined. As reported previously for a different coconut ecotype (Malayan Yellow Dwarf), lupeol methyl ether, isoskimmiwallin, and skimmiwallin were identified as the major components of coconut cuticular wax. The additional compounds were characterized as 3-β-methoxy lupane (lupane methyl ether), lupeol and the acetic acid esters of lupeol, skimmiwallinol, and isoskimmiwallinol, respectively. Minor, nonidentified compounds amounted to some 5% of total wax content and included triterpenoids, sterols, primary alcohols, and fatty acids. The variation detected for parents and progeny with respect to the wax components allowed quantitative trait locus (QTL) analyses for their biosynthetic pathways. A total of 46 QTLs could be mapped onto the coconut linkage map which was extended by amplified fragment length polymorphism and single sequence repeat markers into a high density map with more than 1,000 mapped DNA markers. Several colocated QTLs for different traits were detected reflecting the observed correlations among characters.