Mechanism of Resistance and Inheritance in Glyphosate Resistant Palmer amaranth (Amaranthus palmeri) Populations from New Mexico, USA

Abstract

Two populations of Palmer amaranth from New Mexico have been confirmed to be resistant to glyphosate. In the present study, the molecular basis of resistance and the mode of inheritance of resistance in those populations were investigated. Quantitative real-time polymerase chain reaction analysis indicated up to an eightfold increase in genomicEPSPScopy number in glyphosate resistant plants compared with susceptible plants. The relative genomicEPSPScopy number of resistant plants was positively correlated with the relativeEPSPScDNA expression levels. Eight hours after treatment with glyphosate, the shikimate accumulation levels in resistant plants were negatively correlated with the genomicEPSPScopy numbers. Multiple sequencing of theEPSPScDNA of resistant plants did not reveal any glyphosate resistance-conferring mutations. The evaluation of F1, reciprocal F1, and F2Palmer amaranth families indicated that resistance to glyphosate does not follow a single-gene segregation pattern. Results suggest that theEPSPSamplification is the primary molecular basis of resistance in glyphosate resistant populations of Palmer amaranth from New Mexico.

Physical Mapping of Amplified Copies of the 5-Enolpyruvylshikimate-3-Phosphate Synthase Gene in Glyphosate-Resistant Amaranthus tuberculatus

“…2, 4, and 5) and a negative correlation for shikimate accumulation and glyphosate resistance (Fig. 3) as seen in other GR weeds such as A. palmeri (Gaines et al, 2010;Mohseni-Moghadam et al, 2013), K. scoparia (Wiersma et al, 2015), and L. perenne spp. multiflorum (Salas et al, 2012).…”

Glyphosate resistance: state of knowledge

“…Additional species have recently been reported with EPSPS gene duplication in GR populations, including L. multiflorum , Kochia scoparia , A. tuberculatus and A. spinosus (summarized in Table ). The reported number of duplicated EPSPS gene copies in K. scoparia and A. tuberculatus populations is lower (from four‐ to tenfold) than the Georgia, North Carolina and Mississippi A. palmeri populations (Table ), and similar to the New Mexico A. palmeri population . EPSPS mRNA expression and EPSPS protein levels were found to have a linear correlation with EPSPS genomic copy number in L. multiflorum populations, as well as in K. scoparia populations…”

“…Higher EPSPS copy number correlated with higher‐level resistance in A. palmeri populations from both Georgia and Mississippi . Shikimate accumulation following glyphosate treatment decreased as EPSPS cDNA expression level increased in a New Mexico A. palmeri population . An open question is whether EPSPS genomic copy number in species such as K. scoparia and A. tuberculatus may respond to continuing glyphosate selection pressure and increase to higher levels than previously observed.…”

“…Subsequently, a North Carolina GR A. palmeri population was reported with EPSPS gene duplication from 22‐ to 63‐fold . A New Mexico GR A. palmeri population was sevenfold more resistant than a GS population and had EPSPS gene duplication ranging from two‐ to tenfold, and individuals with EPSPS gene duplication were able to survive label‐rate glyphosate applications (0.82 kg ha −1 ) …”

EPSPS duplication and mutation involved in glyphosate resistance in the allotetraploid weed species Poa annua L.

“…Wiersma et al ., for instance, observed that glyphosate‐resistant K. scoparia plants with a three‐ to nine‐fold increase in EPSPS copy number ( EPSPS : ALS ) had an RI of 3.5–13.8. Similarly, Mohseni‐Moghadam et al . identified glyphosate‐resistant A. palmeri individuals with 1.6‐ to 8.5‐fold increase in EPSPS copy number relative to ALS and an RI of 7.2.…”