STRUCTURE OF GENETIC DIVERSITY IN NATURAL POPULATIONS OF Pinus greggii Engelm.

Abstract

The structure of genetic diversity was studied on 15 allozyme loci in 19 natural populations of Pinus greggii Engelm. in order to determine the level of genetic variability within this species and the degree of genetic differentiation among its populations. A broad genetic diversity was found at the species level (93 % polimorphic loci and a mean of 3. 5 alleles per locus). At the population level, however, genetic diversity was relatively low (31.9 % polimorphic loci and 1.6 alleles per locus on average) with a high proportion of rare (47 %) and private (23 %) alleles. A high degree of genetic differentiation was found among populations (F_st=0.379) but it was not associated to their geographic distribution (only 2 % of the total genetic diversity was attributed to differentiation between geographic regions), unlike the geographic pattern reported for morphological and growth traits of trees. Average genetic distances between pairs of populations were similar in both geographic regions, however, only in the northern region a positive and significant correlation (r = 0.48) was found between genetic and geographic distances of populations.