Submitted to: European Weed Research Society Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 10, 2010
Publication Date: July 12, 2010
Citation: Guermache, F., Bon, M., Jones, W.A., Milbrath, L.R. 2010. A look at ploidy level of Vincetoxicum nigrum (L.) Moench and V. rossicum (Kleopow) Barbar. (Apocynaceae) from the perspective of a study of their invasion success. 15th European Weed Research Society Symposium Proceedings, Kaspovar, Hungary, 12-15 July 2010.
This study aimed to document precisely the patterns of chromosome counts and/or ploidy level variation of Vincetoxicum nigrum (L.) Moench and V. rossicum (Kleopow) Barbar. (Apocynaceae) following their introduction and dispersion in the U.S. and Canada. V. nigrum is native to southwestern Europe whereas V. rossicum originates from Ukraine and southwestern Russia. Both species are invasive in natural areas, abandoned pastures and rural sites in the U.S. and Canada. The hypothesis that species invasiveness had been induced by a switch in ploidy level was addressed.DNA ploidy levels of Vincetoxicum nigrum and V. rossicum (Apocynaceae) were determined by chromosome counts in root tips of seedlings and flow cytometric analysis from fresh foliar tissues.
Chromosome and flow cytometric analyses in this study confirmed ploidy uniformity within native and introduced ranges of all species. In V. nigrum, individuals from France and U.S. were all tetraploid (2n = 4x = 44). In V. rossicum, individuals from Russia and U.S. were all diploid (2n = 2x = 22). V. rossicum shared the same ploidy level as the phylogenetically closely related species V. hirundinaria Medik, that is sympatric to V. nigrum and V. rossicum in its European native range but is not known to be naturalized in the northeastern U.S. Nuclear DNA content (pg/2C) at the species level averaged 1.47 in V. nigrum and 0.70 in V. rossicum . This is the first report of DNA content values for the genus. Our data showed that the invasive spread of North American populations of V. nigrum and V. rossicum was not triggered by differences in ploidy level. Alternative explanations should be sought.