A Trp574–Leu substitution confers resistance to three classes of acetolactate synthase inhibitors in Australian brome grass (Bromus diandrus)

Brome grass (Bromus diandrus) is a prevalent weed in southern Australian cropping regions which causes significant
economic damage in crops and pastures. Before harvest 2023, two populations (named 6-24 and 7-24) suspected of resistance
to imidazolinone herbicides were collected from separate fields. Preliminary screening indicated that these populations
were resistant to several different acetolactate synthase (ALS)-inhibiting herbicides. Therefore, further characterisation of the
level and mechanism of resistance was carried out.

This is the first study reporting a Trp574–Leu mutation as the basis for cross-resistance to ALS-inhibiting herbicides
(sulfonylureas, imidazolinones and triazolopyrimidines) in Australian populations of B. diandrus. Control of these populations
will require strategic use of pre-emergence herbicides and herbicide-tolerant crops in combination with harvest weed
seed control.