Restricted Herbicide Translocation Was Found in Two Glyphosate-resistant Italian Ryegrass ( Lolium multiflorum Lam.) Populations from New Zealand

Abstract

Glyphosate resistance has been found in two populat ions of Italian ryegrass ( Lolium multiflorum ) following many years of glyphosate application in New Zealand vineyards. Dose-response experiments showed that both glyphosa te-resistant Italian ryegrass populations had 10-fold levels of resistance to gly phosate compared to a susceptible population. Possible mechanisms of glyphosate resis tance target site mutation at position Pro-106 of 5-enolpyruvyl-shikimate-3-phosphate synthase gene and alterations in glyphosate absorption/translocation in these popula tions were investigated. Genotyping assays demonstrated that there was no point mutatio n at Codon 106 of the 5-enolpyruvyl- shikimate-3-phosphate synthase gene in either of the resistant populations. Glyph osate- resistant and susceptible populations did not diffe r in 14 C-glyphosate absorption. However, in both resistant populations, much more o f the absorbed 14 C-glyphosate was retained in the treated leaf than occurred in the s usceptible population. Significantly more 14 C-glyphosate was found in the pseudostem region of susceptible plants than resistant plants. Based on these results, it was suggested th at alterations in glyphosate translocation patterns plays a major role in glyphosate resistanc e for Italian ryegrass populations from these New Zealand vineyards. Keywords: EPSP synthase mutation, Glyphosate, Herbicide resi stance, Mechanism of resistance, Weeds.