Genetic resources in maritime pine (Pinus pinaster Aiton): molecular and quantitative measures of genetic variation and differentiation among maternal lineages

Pinus pinaster is a conifer native to western Europe and northern Africa. Following on-going breeding programmes, provenance and progeny trials were established in some of the countries of the speciesʹ range (France, Portugal and Spain) and quantitative traits were measured: growth, stem form, survival and pest and disease resistance, amongst others. Populations from the wide range of P. pinaster were recently screened with molecular markers in order to assess their genetic diversity. Data were obtained using allozymes, chloroplast (cpSSRs) and nuclear (nuSSRs) microsatellites and amplified fragment length polymorphisms (AFLPs). Based on mtDNA-RFLP analysis, three maternal lineages (named "western", "eastern" and "Moroccan") were identified and no population showed a mixed composition. In this study, the imprint that differentiation in putatively isolated glacial refugia (identified by the different maternal lineages) might have left on the nuclear genome was analysed using a wide range of molecular markers and adaptive traits. Multivariate ordination of populations based on nuclear molecular markers (allozymes and nuSSRs) showed a clear clustering of provenances sharing a given mtDNA lineage. However, that clustering was found to be less tight when only quantitative traits were investigated. In P. pinaster, the within-population estimates of gene diversity using different traits were not correlated. Therefore, caution is advisable when designing conservation strategies based on molecular marker studies or a limited number of populations. After these results, we recommend a conservation strategy characterised by gene flow consistent with the current population structure, careful seed transfer among maternal lineages (if any), selection of populations for conservation based on the originality of their allelic composition and definition of Management Units (MUs) based on adaptive traits.