Evolved Glyphosate Resistance in Plants: Biochemical and Genetic Basis of Resistance

Abstract

Resistance to the herbicide glyphosate is currently known in at least eight weed species from many countries. Some populations of goosegrass from Malaysia, rigid ryegrass from Australia, and Italian ryegrass from Chile exhibit target site–based resistance to glyphosate through changes at amino acid 106 of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. Mutations change amino acid 106 from proline to either serine or threonine, conferring an EPSPS weakly resistant to glyphosate. The moderate level of resistance is sufficient for commercial failure of the herbicide to control these plants in the field. Conversely, a nontarget site resistance mechanism has been documented in glyphosate-resistant populations of horseweed and rigid ryegrass from the United States and Australia, respectively. In these resistant plants, there is reduced translocation of glyphosate to meristematic tissues. Both of these mechanisms are inherited as a single, nuclear gene trait. Although at present only two glyphosate-resistance mechanisms are known, it is likely that other mechanisms will become evident. The already very large and still increasing reliance on glyphosate in many parts of the world will inevitably result in more glyphosate-resistant weeds, placing the sustainability of this precious herbicide resource at risk.

Microwave-assisted solvent extraction and analysis of shikimic acid from plant tissues

“…These results are consistent with the range of endogenous shikimate levels found in a study of grass and broadleaf species (Reddy et al, 2008). In this study, levels ranged from about 2 µg g -1 in velvetleaf (Abutilon theophrasti) to approximately 900 µg g -1 in Italian ryegrass (Lolium perenne).…”

“…Weeds are rapidly developing resistance to glyphosate (Nandula et al, 2005;Powles & Preston, 2006). Thus, having a means of quickly identifying and characterizing glyphosate-resistant weed biotypes is important to mitigate their spread and to facilitate their effective management (Singh & Shaner, 1998).…”

Evolution of glyphosate resistance in a Lolium rigidum population by glyphosate selection at sublethal doses

“…Potential mechanistic basis for low-dose-selected glyphosate resistance In field-evolved glyphosate-resistant weed biotypes, two distinct glyphosate resistance mechanisms have been identified (reviewed by Powles and Preston, 2006). In L. rigidum, a reduced glyphosate translocation resistance mechanism and a mutation in the EPSPS target gene have been documented (Yu et al, 2007;Preston and Wakelin, 2008).…”

A Modified phosphate-carrier protein theory is proposed as a non-target site mechanism For glyphosate resistance in weeds

“…The mechanisms of glyphosate resistance can be divided into two groups: those involving changes on target site and those not related to herbicide target site (Powles & Preston, 2006;Powles & Yu, 2010). Mutations at target site and gene amplification are examples of target site resistance mechanisms.…”