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Looks aren’t everything: Hybridization between Dalmatian and yellow toadflax

Date: May 11, 2017

Accurate identification of target weeds is key to effective treatment, even in these closely related toadflax species


Background

Dr. Sarah Ward and her undergraduate scholar Amelia Hadid analyzing toadflax plastid DNA using Boswell’s methodology to determine genetic makeup of plants. Plants were field-collected by Sharlene Sing throughout Montana at known or probable toadflax hybridization sites.
Dr. Sarah Ward and her undergraduate scholar Amelia Hadid analyzing toadflax plastid DNA using Boswell’s methodology to determine genetic makeup of plants. Plants were field-collected by Sharlene Sing throughout Montana at known or probable toadflax hybridization sites.

Two closely related invasive Linaria species, Dalmatian toadflax (Linaria Dalmatica) and yellow toadflax (Linaria vulgaris), have successfully invaded a broad range of ecosystems throughout most of continental North America. The management challenge imposed by the landscape scale of many toadflax infestations, particularly in the West, is further complicated by hybridization between these two weeds. Herbicide and biological control treatments for invasive Linaria are highly species-specific, necessitating the development of a molecular diagnostic tool that can accurately confirm when cryptic hybridization has spontaneously occurred in the field, particularly in plants conforming to typical species appearance.

Research

The initial step in the development of this molecular diagnostic tool involved the extraction of total genomic DNA from individual plants. These were selected from a pool of morphologically unambiguous Dalmatian toadflax or yellow toadflax plants. The trnT-D region was selected for screening for species-specific PCR-RFLP markers after the first five chloroplast DNA (cpDNA) regions evaluated provided insufficient interspecific variation. Separate restriction digests were then performed with the enzymes Alu1, Acc1, and Fok1. The trnT-D region was successfully digested with Alu1, generating restriction fragments that through gel electrophoresis were separated by length. Haplotyping based on species-specific PCR-RFLP markers identified the presence of a single toadflax haplotype, either for Dalmatian toadflax or for yellow toadflax, in the pool of morphologically non-ambiguous plants. Molecular analysis of DNA extracted from an additional pool of hybrid toadflax plants, including field-collected and controlled greenhouse crosses, consistently indicated the presence of both species haplotypes. The 748 bp fragment for yellow toadflax vs. the 608 bp fragment for Dalmatian toadflax was found to be the most reliable and distinct PCR-RFLP polymorphism, both to distinguish between the two toadflax haplotypes, and to confirm hybridization. Results of plastid DNA analysis using single nucleotide polymorphisms (SNPs) in the matK and trnL-F chloroplast-barcoding regions were consistent with PCR-RFLP diagnoses.

Findings

  • Dalmatian and yellow toadflax co-occur in spite of disparate habitat preferences/tolerances
  • Hybridization between these species has been confirmed at multiple sites (MT, CO, WY, ID, WA, BC, AB)
  • Species-specific markers were developed based on PCR-RFLP polymorphisms in the trnT-D cpDNA region, and matK and trnL-F SNP barcoding regions
  • Asymmetric gene flow was confirmed both in controlled greenhouse crosses and field populations of hybrid toadflax, indicating a higher proportion of plants with maternally inherited yellow toadflax cpDNA
  • Species-diagnostic cytoplasmic markers identified the presence of introgressed yellow toadflax genetic material in plants drawn from infestations presumed to be Dalmatian toadflax

Featured Publications

Boswell, Andrew ; Sing, Sharlene E. ; Ward, Sarah M. , 2016
Ward, Sarah M. ; Fleischmann, Caren E. ; Turner, Marie F. ; Sing, Sharlene E. , 2009
Wilson, Linda M. ; Sing, Sharlene E. ; Piper, Gary L. ; Hansen, Richard W. ; De Clerck-Floate, Rosemarie ; MacKinnon, Daniel K. ; Randall, Carol Bell , 2005


Principal Investigators: 
External Partners: 
Ward, Sarah M. Colorado State University, Fort Collins CO
Boswell, Andrew. DuPont Nutrition and Health, Madison WI