Festuca arundinaceagrass and herbicide safeners to prevent herbicide pollution

Abstract

Buffer strips are uncultivated zones left along the boundaries of crops. Buffer strips are used to eliminate or reduce the environmental impact of herbicides. As the efficiency of buffer strips is improved by the presence of non-crop vegetation, we studied the possible role of growing the perennial grass Festuca arundinacea. We investigated the activity in festuca of glutathione S-transferase (GST), which is an enzyme very active in metabolising herbicides. Our results evidence GST activity, which is enhanced by the following compounds: benoxacor, cloquintocet-mexyl, fenchlorazol-ethyl, fenclorim, fluxofenim and oxabetrinil. These synthetic compounds are named herbicide safeners because they protect crop plants against injury from some herbicides without reducing the action of herbicides against the target weeds. The increases in GST activity were found to be concomitant with changes in Vmax and KM, that are kinetic constants related directly to the enzyme concentration in the protein “pull” and inversely to the substrate-enzyme affinity, respectively. In particular, Vmax increase with KM decrease was observed in response to benoxacor, Vmax increases were found in response to fenchlorazol-ethyl, fenclorim, fluxofenim and oxabetrinil, and KM decrease was observed in response to cloquintocet-mexyl. The GST activity was also found to be enhanced by the safeners when it was tested toward the herbicides terbuthylazine and butachlor as substrates. In particular, the increases in GST toward terbuthylazine ranged in the following decreasing order: 154.6%, 91.7%, 89.2%, 88.3%, 82.5% and 30.8% in response to fluxofenim, fenchlorazol-ethyl, fenclorim, oxabetrinil, benoxacor and cloquintocet-mexyl, respectively. The increases in GST toward butachlor ranged in the following decreasing order: 77.0%, 71.2% 59.0%, 41.0% and 33.1% in response to oxabetrinil, benoxacor, fenclorim, fluxofenim and fenchlorazol-ethyl, respectively. A further test, performed to evaluate the relevance of the above effects on a macro-scale level, evidenced 10.1% and 32.7% increased amounts of metabolised terbuthylazine and butachlor, respectively, in response to the addition of benoxacor safener to the herbicide treatments. These results indicate that herbicide diffusion following the runoff of surface waters can be prevented or significantly reduced by vegetating buffer strips with festuca and by the combination of herbicide and a suitable safener.