In order to determine the variability levels among and within natural populations of Machaerium villosum, the genetic structure and the population effective size were analyzed by isozymes. Leaf tissues from three natural fragmented populations were sampled. Thirty-five individuals from the population 2 (Subestação) and thirty individuals from the population 1 (Matinha) and 3 (Bom Sucesso) were sampled. Twenty-six alleles distributed in 10 loci were identified in the populations studied. The estimated diversity index for the three populations revealed average of 2.4 of alleles per locus. The observed medium heterozigosity was higher than the expected for the three populations, revealing an excess of heterozygotes. The proportion of polymorphic loci was 90% in the populations 1 and 2 and 100% in the population 3. The fixation index (f) was negative to all populations. The genetic structure revealed on excess of heterozygotes for three populations (F = -0.121). The genetic divergence between the populations was relatively small (0.061), revealing that 6.1% of the genetic variability found was between populations and 93.9% was within the populations. The effective size estimated for all populations was 32, 48 and 42 individuals respectively. In order to ensure the genetic variability during seed collection twenty-one individuals must be sampled.
effective size; Fixation index; isozyme; polymorhism
