Widespread occurrence of both metabolic and target-site herbicide resistance mechanisms in Lolium rigidum populations

Background

Lolium rigidum populations in Australia and globally have demonstrated rapid and widespread evolution of resistance to acetyl coenzyme A carboxylase (ACCase)-inhibiting and acetolactate synthase (ALS)-inhibiting herbicides. Thirty-three resistant L. rigidum populations, randomly collected from crop fields in a most recent resistance survey, were analysed for non-target-site diclofop metabolism and all known target-site ACCase gene resistance-endowing mutations.

Results

The HPLC profile of [14C]-diclofop-methyl in vivo metabolism revealed that 79% of these resistant L. rigidum populations showed enhanced capacity for diclofop acid metabolism (metabolic resistance). ACCase gene sequencing identified that 91% of the populations contain plants with ACCase resistancemutation(s).Importantly, 70% of the populations exhibit both non-target-site metabolic resistance and target-site ACCase mutations.

Conclusions

This work demonstrates thatmetabolic herbicide resistanceis commonly occurringinL. rigidum, and coevolution of both metabolic resistance and target-site resistance is an evolutionary reality. Metabolic herbicide resistance can potentially endow resistance to many herbicides and poses a threat to herbicide sustainability and thus crop production, calling for major research and management efforts.

Pest Management Science, online.