DETECTION AND PATTERN OF INTERSPECIFIC HYBRIDIZATION BETWEEN GLIRICIDIA-SEPIUM AND G-MACULATA IN MESO-AMERICA REVEALED BY PCR-BASED ASSAYS

Gliricidia sepium provides a variety of products important for rural c ommunities in tropical countries. Native populations in Meso-America c urrently form an important source of seed for distribution to farmers, but concerns centre on mechanisms which may lead to their genetic ero sion, including anthropogenic dispersal and subsequent introgression f rom the related species, G. maculata. Populations of Gliricidia were e xamined genetically using approaches based on the polymerase chain rea ction to test for interspecific hybridization and introgression betwee n G. sepium and G. maculata. Analysis involved 13 RAPD and two RFLP-PC R markers which were identified to have species-diagnostic distributio ns. Data from both approaches corresponded and indicated three locatio ns where multilocus genotypes were consistent with an hybrid origin. D ata at one of these sites was-consistent with introgression following hybridization. The hybrid origin of populations was supported by the i ntermediate geographical location of these sites to 'pure' populations of each species. Analysis of maternally inherited organellar DNA, whi ch involved the detection of SSCPs in mitochondrial DNA amplification products, allowed further delineation of genetic structure among Gliri cidia populations. Mitochondrial data indicated a high degree of organ elle differentiation between sampled locations and identified G. sepiu m- and G. maculata-diagnostic haplotypes. This data supported the inte rpretation of genetic structure based on RAPDs and RFLP-PCR. In additi on, cytonuclear analysis allowed the directionality of gene transfer d uring the formation of hybrid populations to be described. Despite evi dence for the occurrence of interspecific hybridization and introgress ion in Gliricidia, important resource populations of G. sepium on the Pacific coast appear to have retained their genetic integrity. Implica tions in terms of the conservation and utilization of genetic resource s within the genus are discussed.