E. Hidalgo

Spatial genetic structure in continuous and fragmented populations of Pinus pinaster Aiton

Habitat fragmentation, i.e., the reduction of populations into small isolated remnants, is expected to increase spatial genetic structure (SGS) in plant populations through nonrandom mating, lower population densities and potential aggregation of reproductive individuals. We investigated the effects of population size reduction and genetic isolation on SGS in maritime pine (Pinus pinaster Aiton) using a combined experimental and simulation approach. Maritime pine is a wind‐pollinated conifer which has a scattered distribution in the Iberian Peninsula as a result of forest fires and habitat fragmentation. Five highly polymorphic nuclear microsatellites were genotyped in a total of 394 individuals from two population pairs from the Iberian Peninsula, formed by one continuous and one fragmented population each. In agreement with predictions, SGS was significant and stronger in fragments (Sp = 0.020 and Sp = 0.026) than in continuous populations, where significant SGS was detected for one population only (Sp = 0.010). Simulations suggested that under fat‐tailed dispersal, small population size is a stronger determinant of SGS than genetic isolation, while under normal dispersal, genetic isolation has a stronger effect. SGS was always stronger in real populations than in simulations, except if unrealistically narrow dispersal and/or high variance of reproductive success were modelled (even when accounting for potential overestimation of SGS in real populations as a result of short‐distance sampling). This suggests that factors such as nonrandom mating or selection not considered in the simulations were additionally operating on SGS in Iberian maritime pine populations.

Identification and relationships of accessions grown in the grapevine (Vitis vinifera L.) Germplasm Bank of Castilla y Leon (Spain) and the varieties authorized in the VQPRD areas of the region by SSR-marker analysis

A total of sixty-five accessions from the Spanish region of Castilla y León including those authorized in the VQPRD areas were characterized for six SSR loci. All the samples but one unknown were identified by comparison to other databases. Thirty synonymous samples and three cases of homonymy were found out, confirming in most cases ampelographic expectations. Five unique genotypes belonging to local varieties in risk of extinction were detected. Several parameters were calculated to assess the usefulness of the chosen loci in this work. A dendrogram representing the genetic similarities among the accessions was constructed using the neighbor-joining method to investigate possible parentage relationships in the sample, and to explain them from an historical and cultural point of view.

Use of molecular markers for estimating breeding parameters: a case study in a Pinus pinaster Ait. progeny trial

The management of a genetic improvement program is based on the knowledge of the genetic parameters and their relationships to determine the genetic gains. Knowledge of the coefficient of coancestry (θ) is a requirement for efficient progeny testing scheme and for estimating additive variance components for any quantitative trait. When using open-pollinated families, most authors assume that the seedlings are related as half-sibs, but this is not always true. Our aim was to estimate a mean value of the coancestry coefficient of the families present in a maritime pine Pinus pinaster Ait. (maritime or cluster pine) progeny trial originating from seed collected in a clonal seed orchard and to study how deviations from the standard assumption of θ = 0.125 affect heritability estimations. Five highly polymorphic microsatellite markers were scored in 125 offspring from a subsample of five families from the progeny trial. The mean value of the coancestry coefficient of the families present in this progeny trial was 0.130. Differences between the unadjusted and adjusted heritability estimates were more pronounced in wood density (0.609 and 0.586, respectively) than in diameter (0.166 and 0.154, respectively). We conclude that in the trial, the associated error in heritability estimates due to the inclusion of full-sibs, when assuming a standard coefficient of relationship among open-pollinated sibs of 0.250, was low and that this result is robust with respect to the number of families sampled, given unbiased estimates of average relationship among offspring within sib families.

The Atlantic–Mediterranean watershed, river basins and glacial history shape the genetic structure of Iberian poplars

Recent phylogeographic studies have elucidated the effects of Pleistocene glaciations and of Pre‐Pleistocene events on populations from glacial refuge areas. This study investigates those effects in riparian trees (Populus spp.), whose particular features may convey enhanced resistance to climate fluctuations. We analysed the phylogeographic structure of 44 white (Populus alba), 13 black (Populus nigra) and two grey (Populus x canescens) poplar populations in the Iberian Peninsula using plastid DNA microsatellites and sequences. We also assessed fine‐scale spatial genetic structure and the extent of clonality in four white and one grey poplar populations using nuclear microsatellites and we determined quantitative genetic differentiation (QST) for growth traits in white poplar. Black poplar displayed higher regional diversity and lower differentiation than white poplar, reflecting its higher cold‐tolerance. The dependence of white poplar on phreatic water was evidenced by strong differentiation between the Atlantic and Mediterranean drainage basins and among river basins, and by weaker isolation by distance within than among river basins. Our results suggest confinement to the lower river courses during glacial periods and moderate interglacial gene exchange along coastlines. In northern Iberian river basins, white poplar had lower diversity, fewer private haplotypes and larger clonal assemblies than in southern basins, indicating a stronger effect of glaciations in the north. Despite strong genetic structure and frequent asexual propagation in white poplar, some growth traits displayed adaptive divergence between drainage and river basins (QST > FST), highlighting the remarkable capacity of riparian tree populations to adapt to regional environmental conditions.

SSR-based tool for identification and certification of commercial Populus clones in Spain

In order to protect the legitimate interests of the poplar breeders, growers and industries, we have developed a reliable and affordable certification tool for commercial poplars in Spain. We have carried out a genetic description of the 28 commercial clones of the current Spanish National Catalogue using 10 microsatellite molecular markers (SSR). The results clearly show that in the Spanish National Catalogue there are labelling mistakes including synonymies, supported by a combined probability of identity (PI) of 1.18 × 10−9. We have also demonstrate that it is possible to identify all the different clones (genotypes) with only three microsatellites, that show a combined probability of identity of 2.4 × 10−4, and we have optimised the protocols to reduce the time and the economical costs of the analysis. This SSR-based tool could be incorporated in the current certification protocols, to avoid duplication of accessions and identification mistakes.RésuméDans le but de protéger les intérêts légitimes des cultivateurs, des sélectionneurs et des industriels de la populiculture, nous avons mis au point un outil de certification fiable et accessible pour les clones de peupliers commerciaux en Espagne. Nous avons fait une description génétique des 28 clones commerciaux de l’actuel catalogue national espagnol en utilisant 10 marqueurs moléculaires microsatellites (SSR). Les résultats obtenus indiquent clairement que ce catalogue contient des erreurs d’identification, dont des clones synonymes, soutenues par une probabilité combinée d’identité (PI) de 1.18 × 10. Nous avons également démontré qu’il est possible d’identifier tous les génotypes différents avec 3 microsatellites, qui montrent une probabilité combinée d’identité de 2.4 × 10−4, et nous avons optimisé les protocoles afin de réduire le temps et le coût de l’analyse. Cet outil fondé sur les SSR pourrait être intégré dans les protocoles actuels de certification afin d’éviter la duplication des matériaux et les erreurs d’identification.

Extensive Clonal Assemblies in Populus alba and Populus x canescens from the Iberian Peninsula

Riparian vegetation in temperate zones holds great environmental importance and thus its conservation should be a priority. Among riverine tree species, genus Populus stands out, being also a model organism in research. In this work, we present a genetic analysis of the hybrid Populus x canescens and its parent species Populus alba and Populus tremula, with special emphasis in P. alba with which backcrosses frequently occur. This study focuses on the river Douro basin (Spain) where the presence of hybrids has been previously reported. Nuclear microsatellite markers and Bayesian statistical analysis have been used for the detection of hybrids and purebred stands. This methodology has also made possible the study of clonality in the taxonomic continuum P. alba–P. x canescens. Our results highlight the existence of a small number of genotypes accounting for most of the individual trees and stands. Possible causes leading to this situation are discussed. Also, the presence of individuals genetically close to ornamental cultivars is reported for the first time. Finally, concern about the present situation of P. alba genetic resources is brought up.

Mezcla de orígenes, colonización desde un solo refugio glacial o persistencia del pino negral en la Meseta Castellana? Perspectivas utilizando marcadores microsatélites nucleares

Atlantic and Mediterranean populations of maritime pine are very different in quantitative and adaptative traits, even to be considered different subspecies. Different authors have suggested the existence of glacial refugia for this species both in Portugal and eastern Spain based on molecular markers and supported by pollen and fossil records. In addition, based on the existence of high levels of haplotypic variation in this region, the Castilian Plateau is suggested as a contact zone between Atlantic and Mediterranean gene pools of the species. This hypothesis is tested using Bayesian clustering methods and exclusion tests based on multilocus genotypes obtained by genotyping 13 populations with three highly polymorphic nuclear microsatellites. The results show that Castilian Plateau populations constitute a different gene pool by itself that can not be fully originated from the Mediterranean or the Atlantic gene pools, or from a mixture of both. Therefore, three different hypotheses have been considered as plausible causes to give rise to Castilian Plateau maritime pine populations: i) fast colonization of the region from one or more Mediterranean refugial areas, ii) existence of cryptic refugia for the species in the zone, and iii) introduction of exotic material by humans.