I. tinctoria, commonly known as dyers woad, is an invasive mustard that has been introduced into the Western US both intentionally as a traditional source of indigo dye and unintentionally as a contaminant in hay. Across its native range this plant maintains a high degree of phenotypic and genetic variation which means there is a potential for this variation to be carried over to these introduced populations. Populations that maintain more genetic variation subsequently may be harder to control if they undergo rapid evolutionary change. This change can be driven by multiple factors such as founder effects, hybridization and adaptation to novel environments and/or control methods. The focus of this study is to examine the relationship between genetic variation, differences in phenotypic trait means and geographic distribution of this invasive plant. More specifically, we ask whether there is phenotypic or genetic differentiation among plants derived from different introduced populations and can this trait variation in turn be used to separate plants into groups based on their geographic distribution. 

Results/Conclusions

Our results show that there is variation in both phenotypic traits and a neutral genetic marker (Amplified Fragment Length Polymorphisms) in these introduced populations. Preliminary results show that of the 178 alleles screened 86% were polymorphic. The maintenance of genetic diversity in these populations may be due to the predominantly outcrossing breeding system of this species and the likelihood of repeated introduction events. However, regional differentiation among populations may be reduced if individual populations were initiated by large numbers of individuals and/or there has been frequent dispersal of individuals between populations. Preliminary results also suggest that phenotypic variation is correlated with geographic distribution, a potential indicator of evolutionary change and perhaps local adaptation. Plants from different populations grown in a common environment showed a marked difference in flower phenology and other developmental characters and this difference is correlated with latitude. Finally we will discuss how these patterns may have originated given the currently known introduction history of this plant and potential implications for the control of this species