Quantitative trait variation and allozyme diversity of Pinus pinceana

Pinus pinceana Gordon is an endangered pinon pine species found in semi-arid regions of Mexico. The aim of this study was to generate information that is necessary for conserving and sustainably using the species. Factors involved in seed dormancy and germination were studied to evaluate and overcome barriers to the species' ex situ conservation and nursery production. Chemical inhibition and mechanical restriction imposed by the seed coat were the primary factors preventing germination. Allozyme diversity and genetic variation in quantitative traits were estimated to develop a conservation strategy for this species. The relationship between wax quantity and water-stress tolerance of seedlings was examined to determine whether patterns of variation are related to adaptation. P. pinceana had high levels of genetic variation revealed by the number of alleles per locus (2.09), percentage of polymorphic loci (73%), and observed and expected heterozygosity (0.183 and 0.229, respectively). Differentiation among the 13 populations (FST) accounted for 16.5% of the total genetic variation. The multilocus and single-locus outcrossing rates were 0.617 and 0.474, implying high inbreeding due to self-fertilization and crossing among related trees. The variation in quantitative traits among regions, populations within regions and families within populations averaged 11.8, 6.4, and 8.3%, respectively, of the total variation. Individual heritabilities ranged from 0.10 for wax quantity to 0.38 for cotyledon number and family heritabilities varied from 0.13 for root-collar diameter to 0.71 for cotyledon number. The degree of differentiation among regions based on quantitative traits (QSTR) ranged from zero for cotyledon number and total height to 0.55 for wax quantity, and the degree of differentiation among populations within regions (QSTP(R)) varied from 0.053 for root-collar diameter to 0.34 for wax quantity. Although P. pinceana seedlings showed high water-stress tolerance, the association between wax quantity and water-stress was unclear. Similar geographic patterns of differentiation were found for allozyme and quantitative traits and the results indicated that at least seven populations should be included in a conservation strategy to maintain the genetic variation.