Abstract
Twenty-nine provenances of teak (Tectona grandis Linn. f.) representing the full natural distribution range of the species were genotyped with microsatellite DNA markers to analyse genetic diversity and population genetic structure. Provenances originating from the semi-moist east coast of India had the highest genetic diversity while provenances from Laos showed the lowest. In the eastern part of the natural distribution area, comprising Myanmar, Thailand and Laos, there was a strong clinal decrease in genetic diversity the further east the provenance was located. Overall, the pattern of genetic diversity supports the hypothesis that teak has its centre of origin in India, from where it spread eastwards. The analysis of molecular variance (AMOVA) gave an overall highly significant F st value of 0.227—population pairwise F st values were in the range 0.01–0.48. Applying the G″st differentiation parameter, the estimated overall differentiation was 0.632, implying a strong genetic structure among populations. A neighbour-joining (NJ) tree, using the pairwise population matrix of G″st values as input, contained three distinct groups: (1) the eight provenances from Thailand and Laos, (2) the Indian provenances from the dry interior and the moist west coast and (3) the provenances from northern Myanmar. The provenances from southern Myanmar were placed close to the root of the tree together with the three provenances from the semi-moist east coast of India. A Bayesian cluster analysis using the STRUCTURE software gave very similar results, with three main clusters, each containing two sub-clusters, while Bayesian cluster analysis in the Geneland software, exploiting the spatial coordinates of the provenances, resulted in five clusters in accordance with the former results. The implications of the findings for conservation and use of genetic resources of the species are discussed.
Highlights
Teak (Tectona grandis Linn. f.) is a deciduous tree belonging to the Lamiaceae family (The International Plant Names Index 2014) and one of the most important timber species of the world
The observed number of alleles (Na) and the allelic richness calculated via rarefaction (Na(rar)) showed a high correlation of 0.98 even though there is an up to threefold difference in sample sizes
The first studies of genetic diversity in teak in its natural distribution area with molecular markers were conducted with allozymes in the mid 1990s (Kertadikara and Prat 1995a, b; Kjær et al 1996)
Summary
Teak (Tectona grandis Linn. f.) is a deciduous tree belonging to the Lamiaceae family (The International Plant Names Index 2014) and one of the most important timber species of the world. Its wood is renowned for qualities such as resistance to weather and other causes of decay, as well as its elasticity and solid fibre, both of which facilitate woodworking. The wood possesses a high dimensional stability under changing temperature and humidity (Tsoumis 1991). Teak has a large—to some extent geographically dispersed—natural distribution area encompassing parts of India, Myanmar, Thailand and Laos (Kaosa-ard 1981). It grows widely on Java, where presumably it was introduced between the beginning of the fourteenth and sixteenth centuries (Verhaegen et al 2010). The species grows naturally in a wide range of environmental conditions from dry places with only 500 mm annual rain up to areas with 5000 mm—but optimum conditions are in areas having between 1200 and 2500 mm
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