Pine hybrids - a review of their use performance and genetics

Inter-specific hybrid trees planted throughout the world on a commercial ba sis are most common in the genera Acacia, Eucalyptus, Larix, Picea, Pinus a nd Populus although the focal point of this review will include only the ge nus Pinus. The most important forest tree hybrids in this genera include th e inter-specific Pinus hybrids in USA, Korea and Australia. Of those hybrid s that are used commercially, by far the most common are first generation c rosses. In particular, these hybrids appear to be most successful when they are planted in areas outside the normal plantation zones of at least one o f the: parent species. Generalisations about genotype x environment interac tions across genera were not found, and interactions seemed to be specific to the hybrid concerned. published estimates of hybrid genetic parameters w ere not common, but the following general trends were found: (i) heritabili ties calculated from hybrid populations were usually larger when compared t o pure species estimates: (ii) dominance variance varied with taxon, trait and age; (iii) epistatic variance, although only estimated in one case, was negligible when compared with the additive and dominance effects. It is po ssible that inflated heritability estimates were obtained because the infin itesimal model may not be appropriate in hybrid populations. Other alternat ive models should be: investigated in the future. The ability to reliably p redict hybrid progeny performance from general combining abilities of pure species populations depended on trait and hybrid, although it appeared that this ratio was greater for traits of higher heritability. No consistent ev idence was found to support the hypothesis that hybrids may be more adaptab le across environments due to their greater heterozygosity and therefore th eir ability to buffer different environmental stresses. Although there are still gaps in our knowledge of how hybrids behave, some hybrid combinations are without doubt highly successful, and the impact of the use of hybrids in commercial forestry should not be underestimated. (C) 2001 Elsevier Scie nce B.V. All rights reserved.