Phylogeny of Cirsium spp. in North America: Host Specificity Does Not Follow Phylogeny.

Tracey Slotta,Michael Foley,David Horvath

doi:10.3390/plants1020061

Abstract

Weedy invasive Cirsium spp. are widespread in temperate regions of North America and some of their biological control agents have attacked native Cirsium spp. A phylogenetic tree was developed from DNA sequences for the internal transcribed spacer and external transcribed spacer regions from native and non-native Great Plains Cirsium spp. and other thistles to determine if host specificity follows phylogeny. The monophyly of Cirsium spp. and Carduus within the tribe Cardinae was confirmed with native North American and European lineages of the Cirsium spp. examined. We did not detect interspecific hybridization between the introduced invasive and the native North American Cirsium spp. Selected host-biological control agent interactions were mapped onto the phylogenic tree derived by maximum likelihood analysis to examine the co-occurrence of known hosts with biological control agents. Within Cirsium-Cardueae, the insect biological control agents do not associate with host phylogenetic lines. Thus, more comprehensive testing of species in host-specificity trials, rather than relying on a single representative of a given clade may be necessary; because the assumption that host-specificity follows phylogeny does not necessarily hold. Since the assumption does not always hold, it will also be important to evaluate ecological factors to provide better cues for host specificity.

Highlights

The invasion history, genetic diversity associated with founding populations, and evolutionary relationships to proximal native species should be considered in developing biological control management strategies for weeds [1,2]; gaps in such knowledge have led to failures in biological control [3]
Auxin-type herbicides provide some control of Canada thistle; the most effective control is obtained by integration of chemical, mechanical, cultural, and biological control methods [8,14]
We examined genetic variation and population structure within and between C. arvense populations to develop a greater understanding of the biology and reproductive mechanism [21,22]

Summary

Introduction

The invasion history, genetic diversity associated with founding populations, and evolutionary relationships to proximal native species should be considered in developing biological control management strategies for weeds [1,2]; gaps in such knowledge have led to failures in biological control [3]. Assessment of genetic diversity in invasive plant populations can assist in predicting the effectiveness and longevity of herbicidal, biological, and other control measures [4,5,6,7]. Canada thistle (Cirsium arvense (L.) Scop.) is one of the world’s most serious weeds and is a highly invasive plant in temperate regions of North America [8,9]. In 1795, Vermont was the first state to identify it as a noxious weed [11]. Multiple applications of the native bacterial biological control agent Pseudomonas syringae pv. tagetis in conjunction with other control measures were necessary to produce infection and sufficient damage to control growth and seed production of Canada thistle [15]

Results

Discussion

Conclusion