Australasian Science: Australia's authority on science since 1938

Genes Amp Up Resistance in Weeds

Brome grass is a weed of cereal crops that has become resistant to the widely used herbicide glyphosate, but now University of Adelaide researchers have identified the mechanism behind the resistance.

“Great brome (Bromus diandrus) is a significant weed of both crops and pastures across the southern and western Australian cereal belts, causing contamination, yield reductions and damage to meat and livestock,” explains Dr Jenna Malone. “Glyphosate is the most widely used and versatile herbicide in the world and one of the most important herbicides for weed management in Australian agriculture. Loss of glyphosate for brome grass control would cause serious issues for farmers.”

Resistance to glyphosate has been found in recent years in two different populations of great brome. Both populations showed the same mechanism of resistance – amplification of the gene responsible for the enzyme EPSPS, which is targeted by glyphosate. More production of the enzyme overcomes the herbicide’s action.

“It shows yet another way that plants are developing resistance to herbicides,” Malone says. “Until now there have been just three key mechanisms for resistance. Unfortunately it means that there will be even more cases of plants developing resistance to herbicides.”

Research group leader A/Prof Christopher Preston says the research, published in Pest Management Science, “reinforces the need to not overuse glyphosate; to employ good practice of diverse weed management including crop rotations, fallow periods, interspersing with grazing cycles and other control mechanisms”.

The researchers are continuing with further genetic investigations of brome grass to see how the gene amplification occurs and how it is controlled. “If we can discover answers for this, we will have much better knowledge of how the genome of weeds and other plant species can rapidly adapt under stress,” Malone says.