Reintroduction of a dioecious aquatic macrophyte (Stratiotes aloides L.) regionally extinct in the wild. Interesting answers from genetics

1. The reintroduction of a plant species regionally extinct in the wild poses a stimulating conservation challenge. If the species is dioecious and the ex situ preserved population is only of one sex, the challenge is even more difficult. To assess whether the female population of Stratiotes aloides originally studied requires a reinforcement to increase its genetic variation, and to determine from which source male individuals should be taken to re-establish a viable population, the genetic structure of nine different accessions of S. aloides across Europe and Asia were analysed – six native populations and the last three Italian populations, preserved ex situ. 2. Amplified fragment length polymorphism (AFLP) fingerprinting of 190 individuals from these populations was performed using six primer combinations and chromosome counts. 3. AFLP markers revealed medium to high values of genetic diversity at the population level, unexpectedly including residual ex situ accessions. Neighbour-joining tree, PCoA and STRUCTURE analyses indicate the presence of three genetic patterns identifiable in the central-western, central and eastern Europe–Asian populations. Chromosome counts revealed the presence of diploid (2n = 24) and tetraploid (2n = 48) populations. 4. Similarity between populations belonging to different hydrographical basins, and differences between neighbouring populations could be explained through long-distance bird-mediated dispersal events. Genetic analysis showed that reinforcement with female individuals from other European populations to increase the genetic diversity of the Italian female population is not necessary. Surprisingly, the geographically closest male population (Bavaria) to the Po basin is not the best option for male reintroduction. Instead, male individuals should be reintroduced from the Rhine basin (Netherlands) and eastern part of the Danube basin (Romania).