The Basis for Glyphosate Resistance in Rigid Ryegrass (Lolium Rigidum) from California

• Published in: Weed science 2008-03, Vol.56 (2), p.181-188
• Main Authors: Simarmata, Marulak, Penner, Donald
• Format: Article
• Language: English
• Subjects: 5-enolpyruvulshikimate-3-phosphate synthase; alkyl (aryl) transferases; amino acid sequences; Amino acids; application rate; Biological and medical sciences; biotypes; Chemical control; Complementary DNA; enzyme activity; EPSPS; evolution; Fundamental and applied biological sciences. Psychology; genes; Genetic mutation; glyphosate; grass weeds; herbicide resistance; herbicide-resistant weeds; Lolium rigidum; Messenger RNA; metabolic detoxification; Metabolism; molecular sequence data; natural selection; Nucleotide sequences; Nucleotides; Parasitic plants. Weeds; Physiology, Chemistry, and Biochemistry; Phytopathology. Animal pests. Plant and forest protection; Plants; Polymerase chain reaction; resistance mechanisms; single nucleotide polymorphism; Weed science; Weeds
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1614/WS-07-057.1

The occurrence of glyphosate-resistant weeds has been reported after more than 20 yr of extensive use. Rigid ryegrass that evolved resistance to glyphosate was found in Australia and in California. Glyphosate-resistant rigid ryegrass plants were collected from northern California and selected through generations 8 and 5 to segregate the most resistant (R) and sensitive (S) biotypes. The eighth generation of R and the fifth generation of S biotypes survived 6.72 and died from 0.11 kg ae ha−1 glyphosate, respectively. The objectives of this study were to evaluate the role of metabolism in the observed resistance, to study the effect of glyphosate on the activity of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS; EC 2.5.1.19), and to characterize the EPSPS gene in R and S rigid ryegrass. Neither quantitative nor qualitative difference was observed in the metabolism of 14C-glyphosate between the biotypes. Activity of constitutive EPSPS decreased more significantly in the S than R biotype in the presence of 5, 50, 500, and 5,000 µM glyphosate. Inhibition of 50% (I50) of the EPSPS activity by glyphosate was more than 90-fold in S compared to R biotype. Decreased EPSPS sensitivity in the R biotype appeared to be a major contributor to glyphosate resistance in rigid ryegrass from California. Fragments of the EPSPS gene containing 1,320 nucleotides were isolated from mRNA of S and R biotypes. A single nucleotide mutation from cytosine (C) to thymine (T) was identified at nucleotide 301 of the truncated EPSPS gene of the R biotype. This mutation changed the amino acid code from proline (Pro) to serine (Ser), which was similar to that reported for the glyphosate-resistant goosegrass from Malaysia and correlated with glyphosate insensitivity of EPSPS. Nomenclature: Glyphosate; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; rigid ryegrass, Lolium rigidum Gaud. LOLRI