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Eleven highly polymorphic microsatellite markers were used to determine the genetic structure and levels of diversity in 51 natural populations of Pinus oocarpa across its geographic range of 3000 km in Mesoamerica. The study also included 17 populations of Pinus patula and Pinus tecunumanii chosen for their resistance or susceptibility to the pitch canker fungus based on previous research. Seedlings from all 68 populations were screened for pitch canker resistance, and results were correlated to mean genetic diversity and collection site variables. Results indicate that P. oocarpa exhibits average to above-average levels of genetic diversity (A ¼ 19:82, A R ¼ 11:86, H E ¼ 0:711) relative to other conifers. Most populations were out of Hardy-Weinberg equilibrium, and a high degree of inbreeding was found in the species (F IS ¼ 0:150). Bayesian analysis grouped P. oocarpa into four genetic clusters highly correlated to geography and distinct from P. patula and P. tecunumanii. Historic gene flow across P. oocarpa clusters was observed (N m ¼ 1:1-2:7), but the most pronounced values were found between P. oocarpa and P. tecunumanii (low-altitude provenances) in Central America (N m ¼ 9:7). Pinus oocarpa appears to have two main centers of diversity, one in the Eje Transversal Volcánico in central Mexico and the other in Central America. Introgression between P. oocarpa and P. tecunumanii populations appears to be common. Pinus oocarpa populations showed high resistance to pitch canker (stemkill 3%-8%), a disease that the species has presumably coevolved with in Mesoamerica. Resistance was significantly correlated to the latitude, longitude, and altitude of the collection site but not to any genetic-diversity parameters or degree of admixture with P. tecunumanii.

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Eucalyptus urophylla (Timor mountain gum) is an economically important plantation species that occurs naturally in a series of disjunct populations on the volcanic slopes of seven islands in eastern Indonesia. Twelve microsatellite markers were used to investigate the distribution of nuclear genetic diversity among 19 geographically defined E. urophylla populations. High levels of gene diversity were observed throughout the geographic range (H E =0.703 to 0.776). The level of genetic differentiation among populations was low (F ST =0.031), but the amount of differentiation increased with geographic distance. A phenogram produced by a neighbor-joining analysis illustrated that populations clustered according to islands. However, a Bayesian clustering approach revealed a more cryptic population structure comprising two genetically homogeneous groups. Gene flow among the populations is likely responsible for the apparent weak influence of geographic insularity on the genetic diversity and structure of the island species. These findings provide direction for conservation and breeding strategies in E. urophylla.

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A total of 23 provenances or sources of Pinus caribaea var. hondurensis (Sénécl) Barr. et Golf. were tested in 48 provenance–progeny trials in Colombia, Brazil, and Venezuela. In Brazil and Venezuela, 8-year heights were approximately 12 m, while in Colombia, mean 8-year height was less than 8 m. The growth rates of the unimproved material correspond approximately to volumes of 14–15 m3·ha–1·year–1 of wood on sites in Brazil and Venezuela, and 4–5 m3·ha–1·year–1 in Colombia. Provenances had similar growth rankings in the different countries, with a type-B provenance correlation of 0.63. The best native provenances were Limón and Guanaja, Honduras. Improved first-generation sources from Queensland, Australia and Zululand, South Africa, were 5–12% better than the mean of the unimproved provenances, depending on country where planted. Mean single-site heritability for volume growth is approximately 0.18. Potential genetic gain for volume at 8 years from selection within provenance is around 30%. Foxtailing is also under moderate genetic control with heritability around 0.15. Genotype × environment interaction for volume growth is generally higher for tests located in different countries than in the same countries. Selection for age-8 volume using age-5 data would be 93% as effective as selection at age 8.

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Maxipinon (Pinus maximartinezii Rzedowski), which is confined to a single population of approximately 2000 to 2500 mature trees, covers about 400 ha in southern Zacatecas, Mexico. Genetic diversity measured by expected heterozygosity was 0.122, which is moderate for pines. However, percentage polymorphic loci was low, 30.3%. The fixation index (F) of 0.081 indicated only slight heterozygote deficiency. Mating system analysis indicated a significant but low level of se1fing; the multilocus outcrossing rate, tin' was 0.816. The mean of single locus estimates, t s ' was smaller (0.761), perhaps suggesting mating among relatives, although the difference between t m and t s was not statistically significant.The most striking features of maxipifion's genetic structure were that no polymorphic locus had more than two alleles and most alleles at polymorphic loci were at intermediate frequencies. This is in contrast to other pines, which often have three to five or more alleles at some loci and in which the distribution of allele frequencies is U-shaped, most alleles being present at frequencies less than 10% or greater than 90%. A population with only two alleles per locus and at intermediate frequencies could occur if the population had been reduced to an extreme bottleneck and then expanded rapidly before random drift modified allele frequencies. A novel origin from a hybridization event would also explain the results.Significant gametic disequilibrium was detected at several pairs of loci in both maternal and paternal gametes. The presence of disequilibrium is in agreement with an origin from an extreme bottleneck, perhaps even a single seed. Furthermore, it demands that the event be relatively recent. The number of generations, as calculated from the observed mean disequilibrium, suggested that maxipifion derived from an extreme bottleneck four to five generations ago, which is less than 1000 years in this species.