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Logo of annbotAboutAuthor GuidelinesEditorial BoardAnnals of Botany
 
Ann Bot. Dec 2008; 102(6): 997–1006.
Published online Oct 9, 2008. doi:  10.1093/aob/mcn192
PMCID: PMC2712408
The Origin of Clonal Diversity and Structure of Populus alba in Sardinia: Evidence from Nuclear and Plastid Microsatellite Markers
Giuseppe Brundu,1 Renato Lupi,2 Ilaria Zapelli,2 Tiziana Fossati,2 Giuseppe Patrignani,2 Ignazio Camarda,1 Francesco Sala,2 and Stefano Castiglione3*
1Università degli Studi di Sassari, Dipartimento di Botanica ed Ecologia vegetale, Via Muroni 25, 07100 Sassari, Italy
2Università degli Studi di Milano, Dipartimento di Biologia,Via Celoria 26, 20133 Milano, Italy
3Università degli Studi di Salerno, Dipartimento di Chimica, Via Ponte Don Melillo, 84084 Fisciano (SA), Italy
*For correspondence. E-mail scastiglione/at/unisa.it
Received October 10, 2007; Revised December 7, 2007; Accepted August 27, 2008.
Abstract
Background and Aims
Populus alba is a thermophilic forest tree present in the Mediterranean basin. Its habitat is highly fragmented and its distribution range has been subject to long-term human interference, resulting in debate surrounding whether certain populations are native or exotic in origin. In particular, populations from the islands of Corsica and Sardinia are of uncertain origin. While populations of P. alba mainly reproduce sexually, clonal reproduction is also common. The aims of this study were to locate and molecularly characterize the poorly studied island populations of P. alba and compare these with samples from various spatial scales, in order to provide information on the genetic structure and phylogeography of this species. This information will provide evidence on whether the species is native to Sardinia, which is important for the development of conservation strategies.
Methods
DNA extracts were obtained from the following P. alba trees: 159 from Sardinia, 47 from Ticino regional park (northern Italy), 15 acquired from an Italian Germoplasm Bank (IRC; Italian Reference Collection) and 28 from the Mediterranean basin (MB). Genetic polymorphisms were revealed at nuclear and chloroplast DNA (cpDNA) microsatellite loci, both at the island scale (Sardinia) and at broader scales, for comparative assessment of the genetic and genotypic diversity and phylogeography.
Key Results
Based on nuclear microsatellite loci, Sardinian white poplar consists of a small number of genets (26), each of which is represented by several ramets. Despite the uniqueness of the Sardinian haplotypes and the very low value of genetic diversity at the cpDNA level (vK = 0·15), the HT (0·60) and the AR (3·61) values, estimated at the nuclear level for Sardinia, were comparable with those of the other populations and collections.
Conclusions
The uniqueness of the cpDNA haplotypes, the prevalence of clonality and the restricted number of genets recorded suggest that Sardinian white poplar could be a floristic relict of the native flora of the island, which has spread through available habitats on the island mainly by means of vegetative propagation and human activities.
Key words: Populus alba, Sardinia, genets, ramets, phylogeography, native forest species
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