The genetic variation in flowering phenology may be an important component of a species’ capacity to colonize new environments. In native populations of the invasive species Ulex europaeus, flowering phenology has been shown to be bimodal and related to seed predation. The aim of the present study was to determine if this bimodality has a genetic basis, and to investigate whether the polymorphism in flowering phenology is genetically linked to seed predation, pod production and growth patterns. We set up an experiment raising maternal families in a common garden. Based on mixed analyses of variance and correlations among maternal family means, we found genetic differences between the two main flowering types and confirmed that they reduced seed predation in two different ways: escape in time or predator satiation. We suggest that this polymorphism in strategy may facilitate maintain high genetic diversity for flowering phenology and related life‐history traits in native populations of this species, hence providing high evolutionary potential for these traits in invaded areas.

Partial resistance of Populus nigra L. to three races of the foliar rust Melampsora larici-populina Kleb. was studied in a ®eld trial and in laboratory tests, using a collection of P. nigra originating from di erent places throughout France. No total resistance was found. The partial resistance was split into epidemiological components, which proved to be under genetic control. Various patterns of association of epidemiological components values were found. Principal components analysis revealed their relationships. Only 24% of the variance of the ®eld susceptibility could be explained by the variation of the epidemiological components of susceptibility. This variable was signi®cantly correlated with susceptibility to the most ancient and widespread race of the pathogen, and with the variables related to the size of the lesions of the di erent races. Analysis of variance showed signi®cant di erences in susceptibility between regions and between stands within one region. Up to 20% of variation was between regions, and up to 22% between stands, so that these genetic factors appeared to be more di erentiated than the neutral diversity (up to 3.5%; Legionnet & LefeÁ vre, 1996). However, no clear pattern of geographical distribution of diversity was detected.

Abstmct:The balance between sexual and asexual propagation in the establishment of natural stands of Populus nigra was assessed from the genotypes of trees sampled in different natural stands. One site was completely sampled and genotyping proceeded using STS and RAPD markers. Among 118 trees, only four were vegetative copies of other trees of the site. lsozymes were used in four stands, and a method to detect the presence of vegetative copies in a sample is proposed for these markers. No vegetative copies were found in two cases, and a low number of copies was detected in the other two. Observations are reported for seedlings as well as for different modes of vegetative propagation in natural stands. We conclude that sexual and asexual propagation play complementary roles in the dynamics of this species, and that in most cases the adults originate from seedlings.

The European black poplar is a pioneer tree species of the riparian ecosystem. Its natural habitat is exposed to anthropogenic alteration. Overexploitation of the trees, and interaction with a narrow-based cultivated gene pool also contribute to the decline of the species. National programmes for the conservation of Populus nigra exist in most European countries, and it was elected as one of the pilot species in the EUFORGEN programme. The strategies developed in 17 European countries over the species range, and 3 years of collaborative efforts within the EUFORGEN P. nigra Network are reviewed here. The conservation strategies need to be adapted to the biological characteristics and ecological requirements of black poplar. Applied conservation includes ex situ methods for the conservation of genotypes, and, for long-term gene conservation, in situ management of sites in relation to the preexisting natural reserves, or dynamic conservation in the framework of poplar breeding programmes. The social and cultural impact of poplars also interfere with applied conservation. © Inra/Elsevier, Paris Populus / genetic resources / conservation strategy * Correspondence and reprints Résumé-Conservation d'une espèce forestière pionnière, Populus nigra I., En Europe. Le peuplier noir européen est une espèce pionnière de l'écosystème ripisylve. Son habitat est soumis à une forte altération d'origine anthropique. La surexploitation de la ressource, et les interactions des compartiments sauvages et cultivés de la peupleraie, participent également au déclin de l'espèce. Des programmes de conservation de Populus nigra existent dans la plupart des pays européens;