Temperature influences the level of glyphosate resistance in barnyardgrass (Echinochloa colona)

Echinochloa colona is an important summer-growing weed species in cropping regions of northern Australia that has evolved resistance to glyphosate owing to intensive use of this herbicide in summer fallow.

Pot trials conducted at 20 and 30 °C on six E. colona populations showed a significant increase in the level of glyphosate resistance in resistant populations at 30 °C compared with 20 °C. However, there was no influence of growth temperature on glyphosate susceptibility of the sensitive population. Sequencing of the target-site gene (EPSPS) of the six populations identified a mutation at position 106 leading to a change from proline to serine in the most resistant population A533.1 only. EPSPS gene amplification was not detected in any of the resistant populations examined. Examining (14) C-glyphosate uptake on two resistant and one susceptible population showed a twofold increase at 20 °C; however, few differences in glyphosate translocation occurred from the treated leaf to other plant parts between populations or temperatures.

There is reduced efficacy of glyphosate at high temperatures on resistant E. colona populations, making these populations harder to control in summer.