Simulation modelling identifies polygenic basis of herbicide resistance in a weed population and predicts rapid evolution of herbicide resistance at low herbicide rates

The potential for low rates of diclofop-methyl to result in rapid evolution of herbicide resistance in a herbicide-susceptible Lolium rigidum (annual ryegrass) population was demonstrated in a recent crop-field study. In this present study, the data from the crop-field study was used together with simulation modelling to identify possible genetics of the herbicide resistance that was selected for. This analysis clearly indicated that the herbicide resistance was polygenic. Subsequently, the estimated genetic possibilities were used to parameterise a model of herbicide resistance evolution in a simulated crop-field situation, and the potential of different rates of diclofop-methyl (ACCase herbicide) to cause herbicide-resistance evolution in L. rigidum was explored and compared using the calibrated model. The calibrated model outputs indicated that the evolution of diclofop-methyl resistance would generally be faster at low herbicide rates than at higher rates due to the rapid selection of minor gene herbicide resistance traits at low rates and their subsequent recombination by cross-pollination. The results of the study therefore indicate potential risks in herbicide rate cutting and highlight the need for careful scientific evaluation of any herbicide use rate for its potential to select for minor gene herbicide resistance from a weed population.

► Study integrated crop-field data together with simulation modelling.
► Study shows polygenic basis of herbicide resistance at low herbicide rates.
► Study shows risks in herbicide rate cutting, and need for scientific evaluation of herbicide rates.