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Title: Genetic identity and diversity of perennial pepperweed (Lepidium latifolium) in its native and invaded ranges

item Gaskin, John
item SCHWARTZLAENDER, MARK - University Of Idaho
item HINZ, HARIET - Commonwealth Agricultural Bureau International (CABI) - Switzerland
item Williams, Livy
item GERBER, ESTHER - Commonwealth Agricultural Bureau International (CABI) - Switzerland
item Rector, Brian
item ZHANG, DAOYUAN - Chinese Academy Of Sciences

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2013
Publication Date: 4/1/2013
Citation: Gaskin, J.F., Schwartzlander, M., Hinz, H., Williams III, L.H., Gerber, E., Rector, B.G., Zhang, D. 2013. Genetic identity and diversity of perennial pepperweed (Lepidium latifolium) in its native and invaded ranges. Journal of Invasive Plant Science and Management. 6(2):268–280.

Interpretive Summary: Clear species identification of an invasive plant in its native and introduced ranges is a prerequisite for the success of any biological control project. Also, invasions can contain a diversity of genotypes, which can affect how well they are managed by insect agents. To verify the identity of perennial pepperweed populations from the Eurasia that are being explored for biological control agent candidates we collected and analyzed morphological and genotypic data from populations in Eurasia and North America. In addition, we analyzed genotypic data to determine the diversity and distribution of perennial pepperweed genotypes in North America. Our results indicate that perennial pepperweed most probably consists of one species; not two or three as suggested in some recent floristic studies. We found that origins of common invasive genotypes are in Kazakhstan and China, suggesting that these regions should preferentially be searched in potential future foreign exploration for additional biological control agents. We found only eight invasive genotypes in North America, suggesting few introductions or a severe reduction in numbers after being introduced to North America, and little or no sexual reproduction since introduction. The low diversity allowed us to provide seed representing all DNA sequence genotypes for host-specificity and impact studies, which should reduce the risk of any resistance to biological control agents being found after release.

Technical Abstract: Perennial pepperweed is an invasive plant species in North America, native to temperate Eurasia and northern Africa. Effective biological control depends upon correct taxonomic identification. Therefore, we investigated morphological and genetic data (DNA sequences and Amplified Fragment Length Polymorphisms) in its native range, where the species is at times treated as multiple taxa (L. latifolium, L affine and L. obtusum). We also analyzed genetic data to determine the number and distribution of genotypes in the invaded region. Using Bayesian analysis, we found three clusters of genotypes in the native range, but little correlation between these clusters and morphological characters used to distinguish taxa in the native range. Also, we found combinations of morphological character states within many native range plants that are incompatible with current species descriptions, offering no support for splitting L. latifolium sensu lato into three species. In North America 97% of the genetic variation was among populations and there were only eight genotypes in 288 plants, suggesting few introductions or a severe bottleneck, and little or no sexual reproduction since introduction. We found plants in the native range that are genetically similar (88-99%) to six of the eight invasive genotypes, suggesting that Kazakhstan and China are origins for much of the North American invasion.