Genetic polymorphism and phenotypic plasticity : two advantages for the dispersal of Japanese knotweeds

The Japanese Knotweed s.l. population of a riverine region of north-eastern France was examined for a variety of ecological and genetic parameters. The population was dominated by the hybrid Fallopia x bohemica, but the population was morphologically variable and unusual in its being comprised entirely of hermaphrodite 6x and 8x F. x bohemica plants, plus a single aneuploid adult. Chromosome counts are given, and these indicate that both aneuploid and euploid individuals are being produced and becoming established in the study area. It was also found that all plants examined had the F. japonica var japonica chloroplast haplotype. Based on differences in morphology and phenology, the clones were divided into four main categories (1 to 4). Category 1 was widely distributed (nearly 80 % of the area) with the other three having a much more restricted occurrence. Category 1 produced little seed and was not the tallest plant or the clone with the fastest growth. The other categories all produced seed and grew faster. From these results, we can conclude that from an ecological point of view, some clones are more aggressive than others with a similar chromosome composition. Aggressiveness can be linked to the absence of seed production and possession of large leaves, which might allow higher storage of nutrients and better volume of rhizome in the soilPlusieurs populations de renouées en Alsace ont été analysées du point de vue génétique et écologique. Elles sont dominées par l'hybride Fallopia x bohemica, mais celui-ci présente une grande variabilité génétique, et différents types de ploïdie : hexaploïde, octoploïde et aneuploïde. Toutes les plantes ont pour mère Fallopia japonica. Sur la base des différences morphologiques et phénologiques, les clones ont été divisés en 4 catégories. La catégorie 1 est largement distribuée (près de 80 % de l'aire d'étude). Elle produit peu de graines, mais c'est le clone le plus envahissant. D'un point de vue écologique, certains clones sont plus « agressifs » que d'autres de même composition chromosomique. L'agressivité serait liée à l'absence de production de graines et à la présence de grandes feuilles, ce qui permettrait un plus grand stockage des nutriments et un meilleur volume du rhizome dans le sol