Genetic structure and introgression in riparian populations ofPopulus albaL.

Abstract

White poplar ( Populus alba ) is a widespread species of the northern hemisphere. Introgressed populations or hybrid zones with the related species of the European aspen ( Populus tremula ) have been suggested as potential venues for the identification of functionally important variation for germplasm conservation, restoration efforts and tree breeding. Data on the genetic diversity and structure of introgressed P. alba are available only for sympatric populations from central Europe. Here, clonality, introgression and spatial genetic patterns were evaluated in three riparian populations of P. alba along the Ticino, Paglia-Tevere and Cesano river drainages in Italy. Samples of all three populations were typed for five nuclear microsatellite markers and 137 polymorphic amplified fragment length polymorphisms. Microsatellite-based inbreeding co-efficients ( F IS ) were significantly positive in all three populations. Genetic diversity was consistently highest in Ticino, the population with the highest level of introgression from P. tremula . Population differentiation ( F ST ) was low between the Ticino valley in northern Italy and the Cesano valley in central Italy and between the central Italian populations of Cesano and Paglia-Tevere, consistent with a role of the Appenine mountain range as a barrier to gene flow between adjacent drainage areas. Introgression was not the primary determinant of within-population spatial genetic structure (SGS) in the studied populations.

Genetic Biodiversity and Phylogenetic Studies in Poplar by Means of the Metallothionein Multigene Family

“…These moderately high level of both genetic variability and number of haplotypes with respect to the same P. tremula Italian populations [8 Vs 6 - (Salvini et al, 2001)] can possibly be attributed to the fact that the white poplar population here analysed is located in an area (the Cilento) considered as a glacial refugium and a hot spot of biodiversity for several angiosperm species (Cottrell et al, 2005;Fineschi & Vendramin, 2004;Grassi et al, 2009;Petit et al, 2002;Petit et al, 2003). The nSSR analysis carried out on the same population revealed that the expected heterozygosity was relatively high (He 0.460), but in accordance with those reported by Castiglione et al (2010) in the case of three populations distributed along the banks of three rivers in northern and central Italy and with that calculated by Lexer et al (2005) for two populations of P. alba (0.419 and 0.341), and two of P. tremula (0.466 and 0.483 -Lexer et al 2005). Moreover the produced data were also comparable also with those of four different P. tremuloides populations collected in North American [0.460, 0.310, 0.560 and 0.410 -(Cole, 2005)].…”

“…The Cp-SSR analysis performed on the 63 individuals of the Sele river population highlighted a number of alleles (per single locus and in total) and haplotypes comparable with that observed for the white poplar population of the Ticino river previously investigated by this research group (8 Vs 9 haplotypes, Brundu et al, 2008), and slightly higher than that of two populations of the Danube river (8 Vs 5, Lexer et al, 2005), but a little lower than that calculated for a limited number of white poplar specimens collected in different regions of the Mediterranean basin (8 Vs 10, Brundu et al, 2008). However, the higher number of haplotypes observed in the population of the Ticino river could be ascribed to the presence of several hybrids (P. x canescens) derived from the natural cross between P. alba and P. tremula (Fossati et al, 2004;Castiglione et al, 2010), being the last observation further confirmed by Lexer and co-workers in the case of two populations of the Danube and of one of the Ticino (2005Ticino ( , 2010. However, this shouldn't be the case of the Sele river population since PCA analysis clearly separates the white poplars of the Sele from the hybrids of the Ticino (see comments below).…”

“…On the contrary, since evolution favors the occurrence of non-synonymous mutations along the MT polypeptide sequence, the other four genes might be still available to become more specialized into a somewhat different function always linked to metal homeostasis. Therefore, on the basis of our data, we could hypothesize that different paralogous genes belonging to the same multigene family may play for distinctive functions implied in plant metal metabolism and/or response to stress tolerance, as already documented by Kohler et al(2004) and Castiglione et al (2007Castiglione et al ( , 2010Castiglione et al ( and 2011. The sequence analysis of the MT genes shows that exon-intron structure is well conserved within the genome of all analysed Populus spp (three exons and two introns) with the only exception of the MT2a gene.…”

“…Young leaves were collected from single individuals and then stored in absolute ethanol until use. Genetic biodiversity of white poplar natural population of the Sele river was compared with eight reference samples: two clones collected in Sardinia (b33SS, b4SS); further two clones part of a collection of Northern Italy clones and analysed during a previous research project focused on phytoremediation [AL22, AL35 - (Castiglione et al, 2009)], and four hybrids (P. x canescens) collected along the banks of the Ticino river in Northern Italy (# 1, # 13 , # 15, # 2 - Castiglione et al, 2010 (Fermentas, Burlington, Ontario), and sequenced as above described. Each amplicon was sequenced at least two times, using the same PCR primers, and chromatograms were processed by careful visual inspection.…”

Genetic structure of dioecious and trioecious Salix myrsinifolia populations at the border of geographic range

“…In other members of Salicaceae, genetic diversity was usually also higher, i.e. Populus nigra (Hj = 0.139-0.183; Smulders et al 2008) and Populus alba (PPL = 39-72, I = 0.239-0.327; Castiglione et al 2010). One surprising finding is that h and π were negatively correlated with population size.…”