BACKGROUND
This study confirms and characterises glyphosate resistance in two polyploid Echinochloa colona populations from north-eastern Australia.

RESULTS
Glyphosate dose response revealed that the two resistant populations were marginally (up to 2-fold) resistant to glyphosate. Resistant plants did not differ in non-target-site foliar uptake and translocation of ¹⁴C-glyphosate but contained the known target-site EPSPS mutation Pro-106-Thr and/or Pro-106-Leu. Although plants carrying either a single or two EPSPS mutations were glyphosate-resistant relative to the susceptible population, they were still controlled at the field rate of glyphosate (450 g a.e. ha⁻¹) when treated under warm conditions (25/20 °C). However, when treated in hot conditions (35/30 °C), most mutant resistant plants (68%) can survive the field rate, and an increase (2.5 fold) in glyphosate LD₅₀ was found for both the R and S populations.

CONCLUSIONS
This study shows that one or two EPSPS Pro-106 mutations are insufficient in conferring field-rate glyphosate resistance in polyploidy E. colona at mild temperatures. However, control of these mutant plants at the glyphosate field rate is poor at high temperatures, likely due to reduced glyphosate efficacy. Therefore, glyphosate should be applied during relatively mild (warm) temperature periods in the summer growing season to improve E. colona control.