DIVERSIDAD Y ESTRUCTURA GENÉTICA DE Pinus johannis.

Pinus johannis M.-F. Robert-Passini is an endemic pinion nut pine of Mexico that grows in small populations. The objective of this study was to estimate the level of genetic diversity and degree of differentiation among populations in the natural distribution of P. johannis. Mature strobili were collected from 130 tree of four populations. The genotype of each tree was determined in a sample of six megagametophytes, and nine enzyme systems with 16 loci were analyzed. In the four populations the number of alleles varied from 31 to 35. The average number of alleles per locus was 2.1, and the average percentage of polymorphic loci was 88 %. Average heterozygosity was 0.231, and expected average heterozygosity was 0.245. A deficit of heterozygous individuals (FIS=0.116 and FIT=0.176) was found in the four populations together and in each of them. The genetic differentiation among populations was moderate (FST =0.062). Genetic diversity of P. johannis was high with a moderate level of differentiation among populations. [ABSTRACT FROM AUTHOR]