The herbicide safener cloquintocet-mexyl reduces rye-grass (<em>Lolium</em> sp.) sensitivity to an ALS inhibitor and regulates candidate non-target-site-based resistance genes

Abstract

International audienceSafeners enable selective control of weeds in botanically related crops by enhancing or triggering herbicide degradation in crop plants via mechanisms very similar to mechanisms involved in weed non-target-site-based resistance (NTSR). To assess whether safeners could play a role in NTSR evolution, we investigated the eff ect of the safener cloquintocet-mexyl on plant phenotype and on the expression level of 18 candidate NTSR genes in Lolium sp.. Twelve plants in each of three populations were split into 14 tillers each. Tillers from each plant were used in the following modalities: water (control, 2 tillers), Actirob (adjuvant, 2 tillers), cloquintocet-mexyl, pyroxsulam+Actirob (4 tillers), cloquintocet-mexyl+pyroxsulam+Actirob (4 tillers) applied using a custom-built, single-nozzle (110-04, Albuz, France) sprayer delivering herbicide in 300L/ha water at 400kPa (6.6km/h, 23°C, relative humidity 80%). Actirob (1L/ha), pyroxsulam (18.75g/ha) and cloquintocet-mexyl (18.75g/ha) were at the recommended fi eld rate in every modality. Two tillers per plant and per modality were collected 24hours after application to measure the expression of the candidate NTSR genes. The eff ect of cloquintocet-mexyl on plant phenotype was rated 4 weeks after application using the remaining 2 tillers in the last two modalities. Overall, addition of cloquintocetmexyl to pyroxsulam reduced the sensitivity of approx. 25% of the plants tested compared to pyroxsulam alone. A signifi cant up-regulation of 8 candidate NTSR genes was observed 24 hours after application of cloquintocet-mexyl alone. Plants showing a decrease in sensitivity when cloquintocet-mexyl was sprayed with pyroxsulam showed a higher upregulation than other plants in modalities including cloquintocet-mexyl. An additive eff ect of pyroxsulam and cloquintocet-mexyl on gene regulation was observed, with a relative eff ect of cloquintocet-mexyl of up to 48%. We demonstrated that cloquintocet-mexyl can modify herbicide sensitivity and regulate genes potentially involved in NTSR in Lolium sp.