Glyphosate Resistance in Common Ragweed (Ambrosia artemisiifolia) from Mississippi

Glyphosate is one of the most commonly used broad-spectrum herbicides over the last 40 years. Glyphosate acts by inhibiting the enzymatic activity of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which is part of the shikimate pathway. This pathway leads to the production of the aromatic amino acids tyrosine, phenylalanine, and tryptophan, and several essential secondary compounds. Crops such as alfalfa, canola, corn, cotton, soybean, and sugarbeet have been genetically modified to be resistant to glyphosate. Due to widespread adoption of this technology, especially, corn, cotton, and soybean, several weed species in agronomic situations have developed resistance to this herbicide. The mechanism of resistance to glyphosate in these weed accessions may be due to  mutations in the target-site, increased EPSPS gene copy number and expression, and decreased glyphosate uptake or translocation, alone or in combination. The increase in EPSPS gene copy number has been largely attributed to transposon activity in Palmer amaranth, the most devastating agronomic weed resistant to glyphosate.

The current study is concerned with characterizing the magnitude and the molecular mechanism of resistance to glyphosate in a common ragweed (Ambrosia artemisiifolia) accession from Mississippi. We will be conducting studies to investigate glyphosate dose response, ¹⁴C-glyphosate absorption and translocation patterns, and shikimate accumulation in glyphosate-resistant (GR) and –susceptible (GS) populations. Furthermore, the sequence, genomic copy number, and gene expression of EPSPS genes will be compared between GR and GS populations. The results from these studies will help devise meaningful long-term GR common ragweed management strategies.