RIGID RYEGRASS (Lolium rigidum) with GROUP G/9 resistance: (INHIBITION OF ENOLPYRUVYL SHIKIMATE PHOSPHATE SYNTHASE ) Inhibition of EPSP synthase
MUTATION: PROLINE 106 to LEUCINE
Rigid Ryegrass (Lolium rigidum) is a monocot plant in the poaceae family. A single amino acid substitution from Proline 106 to Leucine 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

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..

Kaundun, S. S. ; Dale, R. P. ; Zelaya, I. A. ; Dinelli, G. ; Marotti, I. ; McIndoe, E. ; Cairns, A.. 2011. A novel P106L mutation in EPSPS and an unknown mechanism(s) act additively to confer resistance to glyphosate in a South African Lolium rigidum population. Journal of Agricultural and Food Chemistry 59 : 3227 - 3233.

Glyphosate resistance evolution in weeds is a growing problem in world agriculture. Here, we have investigated the mechanism(s) of glyphosate resistance in a Lolium rigidum population (DAG1) from South Africa. Nucleotide sequencing revealed the existence of at least three EPSPS homologues in the L. rigidum genome and identified a novel proline 106 to leucine substitution (P106L) in 52% DAG1 individuals. This mutation conferred a 1.7-fold resistance increase to glyphosate at the whole plant level. Additionally, a 3.1-fold resistance increase, not linked to metabolism or translocation, was estimated between wild-type P106-DAG1 and P106-STDS sensitive plants. Point accepted mutation analysis suggested that other amino acid substitutions at EPSPS position 106 are likely to be found in nature besides the P106/S/A/T/L point mutations reported to date. This study highlights the importance of minor mechanisms acting additively to confer significant levels of resistance to commercial field rates of glyphosate in weed populations subjected to high selection pressure..

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

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