The biogeographical relationships between far-separated populations, in particular, those in the mainland and islands, remain unclear for widespread species in eastern Asia where the current distribution of plants was greatly influenced by the Quaternary climate. Deciduous Oriental oak (Quercus variabilis) is one of the most widely distributed species in eastern Asia. In this study, leaf material of 528 Q. variabilis trees from 50 populations across the whole distribution (Mainland China, Korea Peninsular as well as Japan, Zhoushan and Taiwan Islands) was collected, and three cpDNA intergenic spacer fragments were sequenced using universal primers. A total of 26 haplotypes were detected, and it showed a weak phylogeographical structure in eastern Asia populations at species level, however, in the central-eastern region of Mainland China, the populations had more haplotypes than those in other regions, with a significant phylogeographical structure (N ST = 0.751> G ST = 0.690, P<0.05). Q. variabilis displayed high interpopulation and low intrapopulation genetic diversity across the distribution range. Both unimodal mismatch distribution and significant negative Fu’s FS indicated a demographic expansion of Q. variabilis populations in East Asia. A fossil calibrated phylogenetic tree showed a rapid speciation during Pleistocene, with a population augment occurred in Middle Pleistocene. Both diversity patterns and ecological niche modelling indicated there could be multiple glacial refugia and possible bottleneck or founder effects occurred in the southern Japan. We dated major spatial expansion of Q. variabilis population in eastern Asia to the last glacial cycle(s), a period with sea-level fluctuations and land bridges in East China Sea as possible dispersal corridors. This study showed that geographical heterogeneity combined with climate and sea-level changes have shaped the genetic structure of this wide-ranging tree species in East Asia.
We examined spatial genetic structure within eight populations of Sitka spruce classified as core or peripheral based on ecological niche, and continuous or disjunct based on species distribution. In each population, 200 trees were spatially mapped and genotyped for eight cDNA-based sequence tagged site (STS) codominant markers. Spatial autocorrelation was assessed by estimating p(ij), the average co-ancestry coefficient, between individuals within distance intervals. The distribution of alleles and genotypes within core populations was almost random, with nonsignificant co-ancestry values among trees as close as 50 m in core populations. In contrast, the distribution of alleles and genotypes within peripheral populations revealed an aggregation of similar multilocus genotypes, with co-ancestry values greater than 0.20 among trees up to 50 m apart and significant, positive values between trees up to 500 m. The relatively high density of reproductive adults in core populations may lead to highly overlapping seed shadows that limit development of spatial genetic structure. However, in peripheral populations with a lower density of adults, the distribution of alleles and genotypes was highly structured, likely due to offspring establishment near maternal trees and subsequent biparental inbreeding, as well as more recent population establishment at the leading edge of post-Pleistocene range expansion. Conserving genetic diversity in peripheral populations may require larger reserves for in situ conservation than required in core populations. These data on spatial genetic structure can be used to provide guidance for sampling strategies for both ex situ conservation and research collections.
-The success of selective breeding for growth rate and subsequent reduction in rotation age in Pinus radiata has resulted in almost 40% of the log constituting juvenile wood in some cases. Juvenile wood properties in radiata pine are known to be limiting in factors such as low density, spiral grain, fibre length, and compression wood. Juvenile wood quality may be improved by breeding for increased stiffness of juvenile wood or an early transition age from juvenile to mature wood. The objective of this study was to investigate the age of transition from juvenile to mature wood and quantify genetic control in time of transition from juvenile to mature wood using 1866 radiata pine samples. Wood samples from two 16-yearold Australia-Wide Diallel (AWD) radiata pine tests and two 28-year-old open-pollinated (OP) progeny tests were submitted to X-ray densitometry procedures. An important finding of this study is the site difference in latewood density transition-age between tests at Flynn and Silver Creek in Gippsland, Victoria (mean = 7.5 y) and at Tantanoola in Green Triangle, South Australia (mean = 12.6 y). This finding suggests that site has a major effect on juvenile-mature transition in radiata pine. We detected moderate levels of genetic control in latewood density transition age that would allow for selective breeding for a shorter juvenile wood formation phase. These results suggest that there may be an opportunity to select for a reduction in transition age and therefore, increase the overall wood uniformity.Pinus radiata / juvenile wood / mature wood / transition age / heritability Résumé -Contrôle génétique de l'âge de transition 'bois juvénile-bois adulte' chez Pinus radiata D.Don. L'amélioration génétique pour la croissance a permis de réduire avec succès la révolution chez le pin radiata mais elle a aussi abouti dans certains cas à faire augmenter la proportion de bois juvénile à près de 40 %. Il est bien connu que plusieurs propriétés (densité, angle du fil, longueur de fibre, bois de compression) sont modifiées dans le bois juvénile du pin radiata. La qualité du bois juvénile peut être améliorée par sélection pour une plus grande rigidité du bois juvénile ou pour une transition plus précoce du bois juvénile-bois adulte. L'objectif de cette étude était d'évaluer l'âge de transition bois juvénile-bois adulte et de quantifier son niveau de contrôle génétique. À cette fin, 1866 échantillons de pin radiata ont été analysés. Des échantillons de bois prélevés en Australie dans deux tests diallèles (AWD) âgés de 16 ans et dans deux tests de descendances issues de pollinisation libre (OP), âgés de 28 ans, ont été analysés par densitométrie à rayons X. Un résultat majeur de cette étude met en évidence un effet environnemental significatif pour l'âge de transition pour la densité du bois d'été. Il est en moyenne de 7,5 années sur les sites de Flynn et Silver Creek à Gippland (Victoria) et de 12,6 années à Tantanoola (Green Triangle, Australie du Sud). Ce résultat suggère que le site a un effet majeur su...
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