SSR markers reveal the population structure of Sri Lankan yellow dwarf coconuts (Cocos nucifera L.)
World coconut germplasm has been classified broadly as tall and dwarf coconuts based on palm stature. Dwarf coconuts are predominantly self-breeding purelines hypothesised to have derived from tall coconuts. Dwarfs are categorized as yellow, green, red and brown on the colour of epicarp and are important as parents in hybridization of coconuts for desirable traits. Sri Lankan yellow dwarfs (SLYD) were observed to have uncommon phenotypes which were not previously reported for dwarf coconuts in the world, and this study was conducted to elucidate the population structure of SLYD. One hundred and two randomly selected SLYD individuals were categorized into three morphological groups and their genotypes were derived at 30 SSR loci. Genotypic data were analysed in PowerMarker 3.2.5 and Structure 2.3.4 software to derive the genetic diversity and the population structure. Unexpectedly high numbrs of alleles, genotypes, gene diversity and heterozygosity values were recorded for SLYD. Four populations were identified within SLYD under admixture model and their morphological variations were determined. Cross pollination between the dwarf and tall coconut varieties followed by the fixing of alleles by subsequent self-pollination was hypothesised to be the cause for the emergence of new genetic groups within dwarf populations. The study demonstrated the formation of new genotypes upon limited cross pollination of even naturally self-pollinating tree crops. The information will be useful for developing strategies for germplasm conservation, practical coconut breeding and determining the domestication and evolution of dwarf coconuts.
KeywordsDwarf coconuts Evolution Genetic diversity Self-pollination Cross pollination
This research was funded by the National Research Council of Sri Lanka under grant no. 11-042. Authors wish to thank Mrs. W. B. S. Fernando of the Coconut Research Institute of Sri Lanka for assistance provided in extraction of DNA.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Data archiving statement
Genotypic data will be submitted to database DRYAD if the manuscript is accepted for publication in the tree genetics and genomes prior to publication.
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