Tools to identify herbicide resistance

Weeds in New Zealand’s land-based production systems cause significant economic harm estimated at ~NZ$500 million per year. Herbicides are one means for managing weed incursions, however herbicide resistance in target plants is a growing issue. Rapid confirmation of incidences of resistance is required for initiating management plans and preventing its spread. Currently, herbicide resistance is confirmed by collecting, growing, then testing suspected plant material with doses of that herbicide – approximately a two-month process.

As part of an AgResearch-led MBIE programme (Managing Herbicide Resistance), we developed genetic tests targeting known changes in plant DNA that underpin herbicide resistance. These ‘Quick’ tests allow us to confirm some forms of herbicide resistance a day after extracting DNA from candidate plants. Our initial focus was glyphosate resistance in perennial ryegrass – a growing problem in vineyards and arable systems. We developed a method that identifies DNA changes linked to glyphosate resistance and susceptibility in perennial ryegrass and have confirmed glyphosate resistance across a range of populations.

We have also established another method (GT-seq) that scans DNA for changes in genes that give rise to resistance to glyphosate, Group A, and Group B herbicides in annual, perennial and hybrid ryegrass. This technology allows a rapid survey of up to 6000 samples per analysis. Using this method, a recent survey of Canterbury farms with suspected herbicide resistance in perennial ryegrass showed that several of plants carried resistance to both Group A and Group B herbicides. This method is being expanded to include wild oats, black grass and Lolium rigidum, a significant weed in Australia.

By developing and implementing these ‘Quick’ tests in other important weed species, we will be providing additional tools in the toolbox to manage herbicide resistance.