The invaders' key to success

press release of October 29, 2010

The number of chromosome copies is one of the success factors of certain invasive plants, along with rapid growth or increased resistance of leaf or root tissues. Those are some of the invasive plants' characteristics that have been mentioned in several studies supported by the National Centre of Competence in Research (NCCR) Plant Survival, a research network whose leading house is the University of Neuchâtel.

Since the publication of lists of invasive plants all around the world, the control of these undesirable species has been a priority, especially during this international year of biodiversity. One way of effectively controlling this pest is by knowing your enemy. This is precisely what several teams from the NCCR Plant Survival are working on. Generally, invasive plants are the result, accidental or not, of a alien plant being introduced in an area that favours its expansion.

At the University of Bern, Wayne Dawson, Markus Fischer and Mark van Kleunen were able to establish an unequivocal link between the relative growth rate of plants from the United Kingdom and their global invasiveness. The study was published at the beginning of October in the Global Ecology and Biogeography journal. It's the first time that such a statistical study was carried out on such a large number of species, in this case 105. The study suggests that plants showing a rapid growth rate during the first phase following germination also are mentioned more frequently in the Global Compendium of Weeds.

Aurélie Thébault, together with her thesis supervisor Alexandre Buttler at the EPFL, François Gillet, Professor at the University of Besançon and Heinz Müller-Schärer, Professor of Biology at the University of Fribourg, have studied the characteristics of success of two invasive species belonging to the Asteraceae family. These are the spotted knapweed (Centaurea stoebe), originating from Europe and responsible for important losses in North American crops and the narrow-leaved ragwort (Senecio inaequidens), originating from South Africa and spread rapidly throughout Europe, especially along railroads and motorways as well as in pastures causing considerable economic losses.

Heinz Müller-Schärer and Patrik Mràz at the University of Fribourg demonstrated that one of these characteristics is the result of a difference in the number of chromosomes present in the DNA. While most living organisms are diploids, having two sets of chromosomes, one from the male parent and the other from the female, certain plants are tetraploids, having four sets.

The researchers compared the invasiveness of three genotypes of each invasive species. Their studies suggest that in North America, where the spotted knapweed was introduced, the tetraploid varieties adapt better than the diploids to the continental and dry climate. In fact, a study carried out at the University of Fribourg and CABI Delémont by Martin Henery and his colleagues showed that in their first stages of development, the tetraploids already acquire a larger mass, their leaves are thicker and richer in carbon and their flowers produce more seeds. Those same characteristics are found in the narrow-leaved ragwort. By increasing the amount of seeds in the inflorescence, the narrow-leaved ragwort becomes more competitive than the neighbouring species, leaving the field wide open for its development and propagation in the new territories where it has been introduced.


PD Dr Mark van Kleunen
Universität Bern
Tel. +41 31 631 4923

Dr. Aurélie Thébault
Tel. +41 21 693 5742

Prof. Dr. Heinz Müller-Schärer
Université de Fribourg
Tel: + 41 26 300 88 35 /  88 50

Senecio inaequidens