EPSPS gene amplification in glyphosate-resistant Bromus diandrus.

ABSTRACT

BACKGROUND: Glyphosate is the most widely used herbicide in the world and has been intensively used to control B. diandrus, a problematic weed of crops and pastures in southern Australia. RESULTS: Resistance to glyphosate was identified in two populations of B. diandrus that were nearly fivefold more resistant to glyphosate than wild-type plants. Both populations contained EPSPS gene amplification, with resistant plants having an average of around 20-fold the number of copies of EPSPS compared with susceptible plants. EPSPS expression was also increased in resistant plants of both populations; however, expression levels were not correlated with the number of EPSPS copies. Amplification of only one of the four EPSPS genes present in B. diandus was detected. Investigation into the inheritance of glyphosate resistance found no segregation in the F2 generation. Every individual in the F2 populations contained between three and 30 copies of EPSPS; however, on average they contained fewer copies compared with the parent resistant population. CONCLUSIONS: Glyphosate resistance in B. diandrus is due to EPSPS gene amplification. Resistance is heritable but complex.