Genetic variability and structure of natural and domesticated populations of Caribbean pine (Pinus caribaea Morelet)

Isozyme analysis of seed samples derived from natural and managed populatio ns of the tropical pine Pinus caribaea vars 'bahamensis' and 'caribaea' was used to assess population genetic structure in its native range and to det ect changes occurring during early domestication of the species. Baseline d ata from natural populations of the two varieties showed that populations s ampled as seed are characterized by high gene diversity (mean H-e = 0.26) a nd a low level of inbreeding( mean F-is = 0.15). A UPGMA tree of genetic re latedness among populations indicates that the two varieties represent dist inct evolutionary units. Within each variety there is significant different iation among populations, and this is greater for the more fragmented popul ations of var 'bahamensis' (F-st = 0.08) than for var 'caribaea' (F-st = 0. 02). Seed from a seed orchard population of var 'caribaea' established with in its natural range showed no change in genetic diversity but did show a r educed inbreeding coefficient (F-is = 0.09) compared with its progenitor po pulations, suggesting a decrease in selfing and/or biparental inbreeding. A bulked seed sample from an exotic plantation of var 'bahamensis' in Austra lia displayed a large increase in the inbreeding coefficient (F-is = 0.324) compared with that found in natural populations, possibly due to elevated self-fertilization. Finally, a bulked seed sample from an exotic plantation population of var 'caribaea' from China showed enhanced genetic diversity, an increase in the inbreeding coefficient and more linkage disequilibrium than its presumed progenitor populations. It was also genetically divergent from them. RFLP analysis of chloroplast DNA variation in the Chinese sampl e suggested that seeds of the related taxa P. elliottii and P. taeda, or se eds derived from hybridization with these taxa growing in the seed producti on area, had been included in the seed crop during harvesting. We conclude that monitoring of appropriate genetic markers may be an effective means of identifying potentially deleterious genetic changes occurring during fores t tree domestication.