RIGID RYEGRASS (Lolium rigidum) with GROUP G/9 resistance: (INHIBITION OF ENOLPYRUVYL SHIKIMATE PHOSPHATE SYNTHASE ) Inhibition of EPSP synthase
MUTATION: PROLINE 106 to SERINE
Rigid Ryegrass (Lolium rigidum) is a monocot plant in the poaceae family. A single amino acid substitution from Proline 106 to Serine has led to resistance to Inhibition of Enolpyruvyl Shikimate Phosphate Synthase as indicated in the table below.		Rigid Ryegrass

Chemical Family	Example Herbicide	Resistance Level
Glycines	glyphosate	Intermediate Resistance < 10 fold

REFERENCES

Bostamam, Y. ; Malone, J. M. ; Dolman, F. C. ; Boutsalis, P. ; Preston, C.. 2012. Rigid ryegrass (Lolium rigidum) populations containing a target site mutation in EPSPS and reduced glyphosate translocation are more resistant to glyphosate. Weed Science 60 : 474 - 479.

Glyphosate is widely used for weed control in the grape growing industry in southern Australia. The intensive use of glyphosate in this industry has resulted in the evolution of glyphosate resistance in rigid ryegrass. Two populations of rigid ryegrass from vineyards, SLR80 and SLR88, had 6- to 11-fold resistance to glyphosate in dose-response studies. These resistance levels were higher than two previously well-characterized glyphosate-resistant populations of rigid ryegrass (SLR77 and NLR70), containing a modified target site or reduced translocation, respectively. Populations SLR80 and SLR88 accumulated less glyphosate, 12 and 17% of absorbed glyphosate, in the shoot in the resistant populations compared with 26% in the susceptible population. In addition, a mutation within the target enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) where Pro₁₀₆ had been substituted by either serine or threonine was identified. These two populations are more highly resistant to glyphosate as a consequence of expressing two different resistance mechanisms concurrently..

Collavo, A. ; Sattin, M.. 2012. Resistance to glyphosate in Lolium rigidum selected in Italian perennial crops: bioevaluation, management and molecular bases of target-site resistance. Weed Research (Oxford) 52 : 16 - 24.

The resistance status of two Lolium rigidum populations (IBAF code 332 and 336) collected in northern Italian vineyards and southern Italian olive groves was investigated. Glasshouse and outdoor pot experiments confirmed that both populations were resistant to glyphosate, exhibiting a resistance index of 4 (pop. 332) and 16 (pop. 336) based on plant survival. Multiple resistance to ACCase and ALS inhibitors was also investigated, and it has been demonstrated that pop. 332 has a lower susceptibility to fluazifop but could be controlled by cycloxydim and flazasulfuron, whereas the other populations tested did not survive herbicides other than glyphosate. The molecular bases of possible target-site resistance were also investigated. Four different patterns of substitution at position 106 were discovered only in the sequences of pop. 336: (i) heterozygous proline-leucine (CCA-CTA); (ii) heterozygous proline-serine (CCA-TCA); (iii) heterozygous leucine-serine (CTA-TCA); and (iv) homozygous serine-serine. The high glyphosate resistance level of pop. 336 indicated that resistance mechanism(s) other than target site are likely to be present. Integrated weed management based on rotation of herbicide mode of action, a careful use of glyphosate, as well as non-chemical weed control, like mowing the vegetation between crop rows, should be implemented to effectively control and limit the dissemination of resistant populations..

Simarmata, M. ; Penner, D.. 2008. The basis for glyphosate resistance in rigid ryegrass (Lolium rigidum) from California. Weed Science 56 : 181 - 188.

The occurrence of glyphosate-resistant weeds has been reported after more than 20 years of extensive use. Rigid ryegrass that evolved resistance to glyphosate was found in Australia and in California, USA. 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 8th generation of R and the 5th generation of S biotypes survived 6.72 and died from 0.11 kg a.i. ha^-1 glyphosate, respectively. An experiment was conducted 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 1320 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..

Fernández-Moreno PT, Bastida F, De Prado R. 2015. First case of glyphosate resistance in France. Agronomy for Sustainable Development 35 : 1469 - 1476.

Glyphosate is a broad-spectrum systemic herbicide used to kill weeds, especially annual broadleaf weeds and grasses known to compete with commercial crops grown around the globe. However, weeds evolve and develop resistance to glyphosate. Until recently, no case of glyphosate resistance had been detected in France. Glyphosate resistance was indeed recently recorded in a Lolium rigidum weed population from a vineyard in the South of France. Here, we studied the mechanisms of this resistance case. Seed samples of L. rigidum were collected from the vineyard where resistance had been detected, as well as from a nearby area that had no known history of exposure to glyphosate. We studied the effect of retention of glyphosate spray, shikimic acid accumulation, glyphosate absorption and translocation, glyphosate metabolism, and the sequence of the enzyme that glyphosate targets in plants, 5-enolpyruvylshikimate-3-phosphate synthase. Our results show that glyphosate absorption decreased by 30 % in the resistant L. rigidum weed. In addition, glyphosate translocation out of the treated leaves was reduced by 52 %. Finally, the resistant biotype had a serine amino acid substitution at position 106 of the predicted protein, instead of the proline amino acid present in the susceptible population. Our results suggest that the resistant population of L. rigidumpresents three different mechanisms of resistance to glyphosate, namely reduced absorption, reduced mobility in the plants, and a mutation in the gene coding for the enzyme targeted by glyphosate..

This case was entered by Todd Gaines Email: todd.gaines@colostate.edu

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