First record of target-site-resistance of poverty brome (Bromus sterilis) to ACCase inhibitors

Abstract

In 2011 reduced efficacy of grass weed herbicides to poverty brome (Bromus sterilis) was observed in oilseed rape on a site in East Hessen. The field was cultivated by using the ploughless tillage system more than 25 years. The site showed high densities of poverty brome (>1000 plants/m²) prior to herbicide treatment. Poverty brome seeds were collected in 2012 in the hessian oilseed rape field and from a site in East Westphalia, where poverty brome appeared at low densities (10 plants/m²) and was not suspected to resistance. The seeds were sown in to pots and plants cultivated. The plants were treated with two application rates (normal dose, double dose) with herbicides of different HRAC-classes. The time of treatment was adjusted to the best expectable treatment/efficiency conditions of the individual herbicides (see chapter 3). Clear differences in efficacy that were caused by herbicide, the origins of poverty brome and the dosages were recorded via visual rating eight weeks after spraying. The herbicides Agil and Focus Ultra were able to control about 90% of the poverty brome plants of the East Westphalia site origin. However, only 20-30% of the Hessian plants could be knocked out by the same herbicides. The ACCase-gene of single powerty brome leaf samples from the hessian site was analyzed after resistance assessment. A molecular genetic analysis on 7 variable positions identified target site resistance: Isoleucine (Ile) was replaced by asparagine (Asn) at position 2041.

Keywords

• ACCase inhibitors
• herbicides
• poverty brome
• target-site resistance