Introduction of Paterson's curse (Echium plantagineum) to Australia: Unravelling the story by DNA sequence analysis

Paterson’s curse (Echium plantagineum L.) is an annual/biennial species in the family Boraginaceae. Native to N.W. Africa, the Iberian Peninsula and Atlantic Western Europe, it is a noxious weed in Australia and has spread over 30 M ha resulting in A$ 250 M annual losses to agricultural industries. Determination of the pathway of introduction is critical to gain further insight into the invasion pathway and process including the sources of propagules. Two hypotheses regarding origin of Australian populations were formulated: 1) introduction as an ornamental via seed importation from England; 2) multiple introductions via South Africa from the Iberian Peninsula and UK. In this study, 131 Australian E. plantagineum samples were analysed using one nuclear gene region (ITS) and three chloroplast gene regions (trnL intron, trnL-trnF spacer and trnH-psbA) and compared with successfully sequenced samples from the Iberian Peninsula (N=43), UK (N=15), South Africa (N=24) and the USA (N=4). A high level of genetic diversity was found in Australia, which suggests a complex history of introduction of Australian E. plantagineum. The most abundant haplotype in Australia was shared with the Iberian Peninsula and UK populations, which suggested that they are both critical source population for Australian E. plantagineum. Importantly, however, 10 of 12 haplotypes found in Australia were represented in South Africa, indicating its potentially important historical role as an intermediate source population for E. plantagineum introductions. The Australian E. plantagineum population was genetically most similar to the UK population and significantly different from other populations, which supports UK E. plantagineum as potential founding population and the Iberian Peninsula and South African populations as additional sources of genetic diversity.