Reference and SSR multi-parent linkage maps for molecular breeding in oil palm (Elaeis guineensis Jacq.)

The oil palm (Elaeis guineensis Jacq.; 2n = 32), an allogamous perennial monocotyledon originating from West Africa, is now primarily grown in Asia, following its introduction into Indonesia in the XIXth century, and placed second after soybean in terms of worldwide vegetable oil consumption by man. Oil palm breeding programmes are all based on a major Sh gene determining three varietal types of fruit, dura (Sh+/Sh+), tenera (Sh+/Sh-) and pisifera (Sh-/Sh-), which are the basis for creating improved tenera seeds, obtained by crossing dura x pisifera, which have the highest natural oil productivity. A general objective of a multinational project funded by the EC under the INCO-DEV program is the development of new molecular resources for molecular breeding in oil palm. This is being achieved by a massive development of microsatellite markers (SSRs), by the construction of reference high density (HD) and consensus multi-parent linkage maps for a more effective detection of worthwhile QTL and for a direct study of their effects depending on their type and the genetic base considered. The topics of this study are the results in developing 410 SSR functional primers pairs in oil palm and their use in the construction of reference and multi-parent linkages maps useful for the further detection of agronomic QTL in the species. The strategy is mainly based on full-sib families, from crosses between 8 different heterozygous parents representing 3 major genetic back-grounds (La Mé, Deli, Yangambi), connected between themselves by common parents, and tested in specific 2 X 2 complete or 4 X 4 incomplete factorial genetic designs. Dominant AFLP and co-dominant SSR markers are being used for building up the reference HD linkage map of a LM2T X DA 10D control progeny. The degree of segregating polymorphism is relatively high in the chosen map population with an average of 69% polymorphic SSR loci and of 11 AFLP fragments per primer combination. A total of 282 SSRs and of 1118 AFLPs were produced on that cross. The actual map of the LM2T genitor contains a total of 591 markers (174 SSRs; 416 AFLPs and the Sh morphologic gene). It has a total length of 1308 cM. The 16 linkage groups corresponding to the 16 oil palm chromosomes vary between 40 and 152 cM in length. The SSR markers, relatively well-distributed along the genome, present as many as 40% of common markers that will allow to construct the HD map of the reference cross as well as connected SSR maps of the whole map system. (Résumé d'auteur