Population genetic structure of Milicia species characterised by using RAPD and nucleotide sequencing L.

Milicia species (M. excelsa and M. regia, Moraccae, the irokos) are among the most useful indigenous rain forest tree species in Africa. They are not grown in plantations but extracted from the natural forest at an unsustainable rate. The major constraint on cultivation and afforestation is the gall-forming insect Phytolyma lata, which destroys seedlings through gall formation, causing dieback of the shoot. Genetic diversity studies should aid the design of conservation and resistance-breeding strategies. This study, therefore, aimed to investigate the genetic variability in Milicia from three West African countries and the power of bulk-family DNA in partitioning of genetic diversity. Genetic variation within and between 5 natural populations of Milicia from Ghana, Cote d'lvoire and Sierra Leone was investigated using random amplified polymorphic DNA (RAPD) and non-coding chloroplast DNA sequencing. RAPD analysis of 41 DNA samples with 8 primers produced a total of 74 bands with 40 bands (54.1%) being polymorphic, Dendrogram analysis produced 2 major clusters separating dry and moist/wet ecotypes. Sub-clustering further separated accessions by forest type and/or geographic region. A greater proportion of the total genetic variability was attributed to variation between populations (62.2%) than within populations (37.8%). Sequencing of chloroplast tRNA(Leu) intron (cptrnL) and intergenic spacer (cpIGS) between cptrnL and tRNA(Phe) (trnF) did not show any variation. The RAPD analysis suggests that trees from wet/moist sites are mostly M. regia, while those from dry sites are mostly M. excelsa. Sequencing results, however, suggest that the two species are closely related. These results are discussed with reference to conservation strategies.