Resistance to glyphosate inLolium rigidum.I. Bioevaluation

Abstract

Glyphosate is the world's most widely used herbicide. It is nonselective and has been used to control a broad range of weed species for the past 20 yr, without the appearance of resistant weed biotypes. However, a biotype ofLolium rigidumfrom a field in Northern Victoria, Australia, in which glyphosate had been used for the past 15 yr, failed to be controlled by label recommended rates. Based on LD50values from pot dose-response experiments, this biotype exhibited resistance to glyphosate and was nearly 10-fold more resistant compared to the susceptible biotypes tested. The biotype was resistant to three different salts of glyphosate. The biotype was also nearly threefold more resistant to diclofop-methyl but was susceptible to other commonly used selective and broad-spectrum herbicides. Between the two-leaf and tillering stages of development, a susceptible biotype exhibited a small but significant decrease in tolerance to glyphosate, whereas tolerance of the resistant biotype remained unchanged with age. The resistant phenotype was verified in experiments in which seed was germinated in the presence of glyphosate. Observations on shoot and root growth of seedlings in these experiments suggested that the resistance mechanism might be associated more with the shoot than with the root.

Distinct non-target site mechanisms endow resistance to glyphosate, ACCase and ALS-inhibiting herbicides in multiple herbicide-resistant Lolium rigidum

“…Glyphosate resistance was Wrst reported in L. rigidum from Australia , and now has been reported in several populations of L. rigidum in Australia (Pratley et al 1999;Lorraine-Colwill et al 2003;Neve et al 2004;Wakelin et al 2004), USA (Simarmata et al 2003), South Africa (Yu et al 2007a), and in L. multiXorum from Chile (Perez-Jones and Kogan 2003) and USA (Perez-Jones et al 2005). The major resistance mechanisms thus far reported for glyphosate-resistant weeds are reduced glyphosate translocation (non-target site based) and EPSPS point mutation (target-site based) (reviewed by Powles and Preston 2006;Preston and Wakelin 2008;Shaner 2009).…”

Mutations and amplification of EPSPS gene confer resistance to glyphosate in goosegrass (Eleusine indica)

“…For other analyses, duplicate clones were generated from representative (GR) and (S) individuals by removing approximately 10 tillers and subtending root mass per plant, which were then repotted in pots as described before. For the EPSPS gene sequencing, all the clones were challenged with a sublethal spray of glyphosate (Pratley et al 1999).…”

Glyphosate, paraquat and ACCase multiple herbicide resistance evolved in a Lolium rigidum biotype

“…Despite the rarity of glyphosate and paraquat resistance alleles, over-reliance on these herbicides results in the evolution of resistance. Biotypes of glyphosate resistant Lolium from several countries are known (Powles et al 1998;Pratley et al 1999;Perez and Kogan 2003;Simarmata et al 2003;Perez-Jones et al 2005a; recently reviewed by Powles and Preston 2006), and paraquat resistant L. rigidum has evolved (Yu et al 2004a). However, this is the Wrst report of multiple resistance to both glyphosate and paraquat (as well as to ACCase-inhibiting herbicides).…”