Molecular markers to assess genetic diversity and structure of Pterocarpus officinalis Jack and its associated micro-organisms in the Marshy forests

The influences of the combined swamp environment and geographical structure within the natural range of tree/rhizobia symbiotic systems are poorly documented. Pterocarpus officinalis was selected as an interesting species to analyze the genetic structuring of two symbiotic partners in a continental and insular system. We sampled 7 P.officinalis populations in different West Indies islands (Guadeloupe, Dominica, Martinique, Puerto Rico) and in French Guiana on the continent. Between 20 and 30 individuals were sampled in each population and for each individual, 2 leaves and 5 nodules were collected for future molecular analyses. Genetic diversity of P.officinalis was assessed through nuclear and cloroplastic microsatellite. The genetic diversity of symbiotic bacteria isolated from P.officinalis nodules was investigated by sequence analysis of 16S-23S rDNA intergenic spacer (IGS). Bacterial diversity results showed a very low genetic diversity in insular system and a high diversity on the continent. Ours first results showed for the plants a strong population structure, with a low genetic diversity in insular system and a high diversity on the continent. Chloroplastic microsatellite analyses showed however a limited genetic structure (compared to other tree species) which could be explained by the water floating mode of seeds dispersal. Nuclear microsatellite analyses showed complex pattern of correlation between geographic and genetic distance. These results suggest a parallel pattern in molecular diversity for the plants and their bacteria, possible consequence of similar impact of evolutionary forces (limited gene flow and strong genetic drift). (Texte intégral