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.
