POPULATION-STRUCTURE IN GLIRICIDIA-SEPIUM (LEGUMINOSAE) AS REVEALED BY ISOZYME VARIATION

Gliricidia sepium (JACQ.) WALP, is a woody legume native to seasonally dry sites in Meso-America. It has been introduced to many other parts of the tropics, where it is utilised as a source of fuelwood, living fences, animal fodder and green manure by rural communities. These int roductions have. however, been founded on a narrow, or unknown, geneti c base, and poor growth performance has been reported at a number of l ocations. There is. therefore, a need to diversify the genetic base of this species in domestication, and to explore its population structur e as a basis for this diversification. Here we report the use of isozy me markers to investigate the distribution of genetic diversity within and among populations of G. sepium. Marked differentiation between po pulations (F-ST = 0.172) was observed, although most variation occurre d within populations. Averaged over all populations, there was a mean number of alleles per locus (A) of 2.0, a mean percentage polymorphic loci (P) of 60% and a mean observed heterozygosity (H-o) of 0.238, val ues which suggest a rather higher level of genetic diversity than thos e reported from other comparable species. The values of these variable s, however, differed considerably between populations, those believed to be native maintaining higher levels of variation than those believe d to be naturalised or introduced. Some of the most genetically divers e populations have also been recommended for forage and fuelwood produ ction, indicating that there is a sound basis for the genetic improvem ent of this species.