Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 28, 2013
Publication Date: October 20, 2013
Citation: Nandula, V.K., Wright, A.A., Molin, W.T., Ray, J.D., Bond, J.A., Eubank, T.W. 2013. EPSPS amplification in glyphosate-resistant spiny amaranth (Amaranthus spinosus): a case of gene transfer via interspecific hybridization from glyphosate-resistant Palmer amaranth (Amaranthus palmeri. Pest Management Science. pg.3754. doi:10.1002. Interpretive Summary: The rapid and widespread adoption of glyphosate-resistant crops, associated with the intense use of glyphosate and lack of rotation with non-glyphosate-resistant crops has resulted in evolution of several glyphosate-resistant weed species, including spiny amaranth in Mississippi. Glyphosate-resistant spiny amaranth, given the ability to germinate over a broad range of temperatures, prolific seed production, and ability to hybridize with Palmer amaranth, may pose management problems in the future and serve as an alternate host for certain insect pests and diseases. Scientists from the Crop Production Systems Research Unit (USDA-ARS), other ARS research units, and Mississippi State University conducted studies to confirm and quantify the magnitude of glyphosate resistance in spiny amaranth from northeastern Mississippi, to characterize the molecular mechanism of glyphosate resistance, and to investigate the possible role of field-level interspecific hybridization between this spiny amaranth and natural infestations of glyphosate-resistant Palmer amaranth. Glyphosate-resistant spiny amaranth biotypes exhibited a 5-fold increase in resistance compared to a glyphosate-susceptible biotype. 5-enolpyravyl shikimate-3-phosphate synthase (EPSPS), target enzyme of glyphosate, was amplified 26 to 37 times and expressed 17 to 23 times more in glyphosate-resistant spiny amaranth biotypes than in a susceptible biotype. Thus, glyphosate resistance in spiny amaranth is caused by amplification of the EPSPS gene, which may have been due to crossing with glyphosate-resistant Palmer amaranth. This research has profound implications for glyphosate resistance management, especially, in pigweeds.
Technical Abstract: Amaranthus spinosus, a common weed of pastures, is a close relative of Amaranthus palmeri, a problematic agricultural weed with widespread glyphosate resistance. These two species have been known to hybridize, allowing for transfer of glyphosate resistance. Glyphosate-resistant A. spinosus was recently suspected in a cotton field in Mississippi. Glyphosate-resistant A. spinosus biotypes exhibited a 5-fold increase in resistance compared to a glyphosate-susceptible biotype. EPSPS was amplified 26 to 37 times and expressed 17 to 23 times more in glyphosate-resistant A. spinosus biotypes than in a susceptible biotype. EPSPS sequence was similar between the resistant and susceptible A. spinosus biotypes. EPSPS in resistant A. spinosus plants was identical to the EPSPS in glyphosate-resistant A. palmeri, but differed at 29 nucleotides from the EPSPS in susceptible A. spinosus plants. PCR analysis revealed similarities between the glyphosate-resistant A. palmeri amplicon and glyphosate-resistant A. spinosus. Glyphosate resistance in A. spinosus is caused by amplification of the EPSPS gene. Evidence suggests that at least part of the EPSPS amplicon from resistant A. palmeri may be present in glyphosate-resistant A. spinosus. This is likely due to a hybridization event between A. spinosus and glyphosate-resistant A. palmeri somewhere in the lineage of the glyphosate-resistant A. spinosus plants.