No abstract

Genetic-parameter estimates and parental breeding-value predictions were compared from open-pollinated and control-pollinated progeny populations of Eucalyptus globulus and two populations of E. nitens. For E. globulus there were two types of open-pollinated populations (native stand open-pollinated and seed orchard open-pollinated) and two types of control-pollinated populations (intra-provenance and interprovenance full-sib families). For E. nitens there were two populations, a seed orchard open-pollinated population and intra-provenance full-sib families. Progeny tests were established across multiple sites and 2-year height and diameter were measured and volume calculated. Genetic parameters from native stand open-pollinated E. globulus were unlike the parameters from the other three E. globulus populations; heritability estimates were severely inflated, presumably due to high levels, and possibly differential levels, of inbreeding depression relative to the other populations. Estimates of dominance variance in the E. globulus full-sib populations were high, but were zero in the E. nitens population. Correlations among parental breeding values, predicted using data from the different populations, were generally low and non-significant, with two exceptions: predictions from the two E. globulus full-sib populations were significantly correlated (r=0.54, P = 0.001), as were predictions from the E. nitens seed orchard OP and full-sib population (r = 0.61, P = 0.08). There was some indication that superior parents of E. globulus native stand open-pollinated families also tended to have above-average breeding values based on the performance of intra-provenance full-sib offspring. The consequences of these results for exploitation of base-population collections from native stands are discussed.

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.