Napoleonian legacy in Populus nigra populations

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إنجليزي. Black poplar (Populus nigra), a major dioecious tree species in riparian ecosystems in Europe, is endangered by loss of habitats and gene flow from cultivated poplars. These included not only exotic species present in commercial plantations but also ornamental species widely planted known as cv. ‘Italica’ (Lombardy poplar). The latter origin is supposed to be Middle East, and was introduced in European landscape 250 years ago, and in France during the Napoleonian era. This cultivar belong to the P. nigra species and is known to be the male parent of several widely planted interspecific hybrid cultivars.A 12K Infinium beadchip array was developed to study P. nigra diversity in Western Europe (Faivre-Rampant et al. 2016). A total of 1150 P. nigra individuals from natural stands and progenies from controlled crosses were genotyped. The cv. ‘Italica’ and related ancient cultivars were also included. Structure of the populations from natural stands studied with a total of 7896 SNPs reflected the geographical distribution of the species in major river basins but a high level of admixture between populations remained. A non-negligible part of this admixture may be due to ‘Italica’ genetic background as this cultivar and introgressed individuals formed a distinct genetic pool. The rate of introgression differed between populations, French populations being the mostly affected. Comparison with controlled crosses and ancient cultivars allowed to resolve pedigree of some introgressed individuals.We identified a set of alleles at SNP markers that are specific to ‘Italica’ which allow us to diagnose hybridization but also introgression in advanced generations. This work showed that the impact of the presence of P. nigra cv. ‘Italica’ in European landscapes on diversity of P. nigra populations is unexpectedly high.