Nadya Wahid

Genetic Structure and Variability of Natural Populations of Maritime Pine (Pinus pinaster Aiton) in Morocco

Abstract The estimation of genetic diversity using molecular markers is a major component of genetic conservation programs. In its range, Maritime pine has been extensively studied using different molecular markers and quantitative traits. However, Moroccan populations have been usually represented only by a few typical locations in the Middle Atlas (e.g., Tamjout). To describe the genetic structure and variability of maritime pine in Morocco, eleven populations of this species comprising all major geographic regions (Rif, Middle Atlas and High Atlas) were studied using allozyme markers. A total of 471 samples were analyzed using polyacrylamide gel electrophoresis (PAGE) of eight enzyme systems encoded by 19 loci. Genetic variation was lower in Morocco than in other ranges of the species. However, genetic diversity was structured and a high differentiation among populations (θ = 10.44%) and a moderate correlation between genetic and geographic distances were found (0.350). Three main groups of populations can be distinguished based on genetic distances: (i) Mediterranean Coastal, (ii) Occidental Rif and Middle Atlas and (iii) High Atlas. The populations from Middle Atlas presented the lowest values of allelic richness and gene diversity whereas the populations from Rif showed a considerable amount of genetic variability. Human impact and isolation are major factors explaining population genetic structure of maritime pine in Morocco. Overexploitation of the forest by intensive cattle grazing and land speculation are suggested to be active mechanisms currently deploying the genetic resources of this species.

Range-wide genetic structure of maritime pine predates the last glacial maximum: evidence from nuclear DNA

Using nuclear simple sequence repeats (nuSSRs), we determined the genetic variability in the natural distribution range of maritime pine (Pinus pinaster) in the western Mediterranean region. We analysed the role of global and significant climatic fluctuations in driving the evolutionary diversification of this species. We attempted to determine the impact of the last glacial maximum (LGM) and human activity on genetic variation and to identify the effect of bottlenecks, admixing, migration, time to the most recent common ancestor (TMRCA), and recent splits. A total of 972 individuals were analysed. The sample represented 27 natural populations from the western Mediterranean region, which encompasses most of the natural range of P. pinaster. Using eight nuSSRs, we analysed genetic diversity indices for each population and group of populations. We also examined the interpopulation structure by the frequency and distance method and investigated genetic barriers, signals of historical demographic fluctuations, phylogeographic structure, admixing, rate of mutation, migration, as well as testing the hypothesis of isolation by distance (IBD). Both cluster analyses showed similar population genetic structure with three genetic barriers that divided the samples into four large groups. Intensive migration was only detected during the period of the last glacial maximum (LGM), which permitted the mutation rate of the markers used to be calculated. The majority of the population was found to exhibit signs of a recent bottleneck and its timing showed a clear northeast-southwest geographic distribution. A clearly defined phylogeographic structure (Nst > Gst and Rst > Gst ) under IBD was established, and showed the highest divergence between groups of populations separated by physical barriers, such as the Strait of Gibraltar, the Mediterranean Sea and the Pyrenees. The high level of intergroup genetic differentiation (ΦIS = 20.26) was attributed to a long historical isolation (which occurred before the last 18 000 years) between the principal maritime pine population groups that occurred due to physical barriers that limited pollen and seed transfer, combined with a minimal effective radius of distribution. The low level of genetic diversity among the populations was combined with genetic drift and a recent bottleneck during the period of human activity. Significant migration across barriers was due to spontaneous phenomena during the LGM, which had no significant impact on the genetic structure owing to its relatively short duration and the fragmented species. The phylogeographic structure under the assumption of IBD was well established for P. pinaster in each of the principal population groups.

Genetic Control and Nursery-Plantation Genotypic Correlations for Growth Characteristics of White Spruce Somatic Clones

Height and diameter of white spruce clones were measured over two growing seasons in a forest nursery and for 4 more yr at two field sites. Clonal heritability (Hc 2) was moderate and stable in the nursery, but decreased with age, reaching 0.26 and 0.11 for height and 0.14 and 0.04 for diameter, respectively, at the two field sites. Height exhibited weak to moderate Hc 2 and strong genotypic correlations with the different growth characteristics. The strong age-age genotypic correlations (≥0.809) and nursery-plantation correlations (≥0.347) for height indicate that selection for height can be conducted at a young age thus reducing the costs of clonal tests.

Genetic parameters and clonal variation in growth and nutritional traits of containerized white spruce somatic seedlings

Abstract Clonal forestry can significantly increase forest productivity and its establishment requires a high level of clonal variation to maximize genetic gain and diversity. An evaluation of the genetic parameters of clones at a juvenile stage is necessary to better understand the amplitude of clonal variability and the degree of genetic control. The analysis of variance of white spruce clones showed a highly significant clonal effect for the majority of the growth characters at the end of both growing seasons and for the mineral status at the 2+0 stage. Our results reveal that height exhibits a high clonal heritability value which remained stable over the two growing seasons (H2 c= 0.60). Strong genotypic and phenotypic correlations were observed between height and diameter at the end of the first growing season and between height and the rest of the growth characters at the end of the second growing season. The strong clonal variation, genetic control and genetic correlation particularly of height found in this study indicate that the selection ability of the best performing clones is possible for intensive forest management.

Évaluation de la structure et de la variabilité génétiques des populations naturelles du pin d'Alep (Pinus halepensis Mill.) au Maroc à l'aide de marqueurs isoenzymatiques

Abstract Aleppo pine (Pinus halepensis Mill.) is a species threatened by anthropogenic overexploitation due to climate change. To contribute to its conservation, we evaluate the structure and the genetic diversity of the natural pine populations. We studied the genetic diversity of 14 populations (Rif, Middle Atlas, eastern Morocco and High Atlas) using an isoenzymatic marker. The results of the analysis indicated that the genetic variation of pine in Morocco is modest in comparison with other Mediterranean provenances. However, the study revealed a high coefficient of differentiation among populations (Fst = 9.5%). Two main population groups were identified based on genetic distances: South—West and North-East.

Variabilité du potentiel germinatif des semences de certaines populations marocaines de pin maritime (Pinus pinaster Ait.) sous conditions contrôlées

Abstract Seeds germination obtained from ten Moroccan maritime pine populations growing in three biogeographic areas were studied under controlled photoperiod length and temperature for two pretreatments (stratifications at 4 °C and imbibition with water). Significant differences in germinal potential were noted between batches of seeds. Whereas a relative homogeneity of the germinal behavior of various batches of seeds with respect to duration 12, 48 and 72 h of imbibition was noted. However, the duration of stratification has a differential effect on the speed of germination (T50) between populations and even within the same population. Correlation between geographical parameters, percentage of germination (%G) and T50 shows that longitudinal variations explain about 46% and 39% of the variance, respectively.