Selectivity of Iodosulfuron-Methyl to Oat Cultivars

ABSTRACT Weeds are among the main constraints to high grain yield on hexaploid oat (Avena sativa), but there are few herbicides registered for weed control on this cereal crop. The objectives of this study were to evaluate the impact of the iodosulfuron-methyl on grain yield of elite oat cultivars and investigate the mechanism of oat tolerance to this herbicide. A field experiment conducted in 2012 demonstrated there was no difference on grain yield between cultivars URS Guará and URS Guria, when iodosulfuron-methyl was used up to 4.5 g ha-1. Likewise, experiments from 2013 have demonstrated that iodosulfuron-methyl, at 5 g ha-1, did not affect the oat grain yield of the genotype UFRGS 14, but affected it on the cultivars URS Guará and URS Guria. In 2014, the oat grain yield of five cultivars, including URS Guará, URS Guria and UFRGS 14 was reduced by iodosulfuron-methyl even at only 2.5 g ha-1. The activity of the ALS enzyme, extracted from oat plants, was sensitive to iodosulfuron-methyl. The increment of the iodosulfuron-methyl effect on oat plants treated with herbicide-detoxification inhibitors (malathion + chlorpyrifos), or the reduction of the herbicide efficacy in plants sprayed with the stimulator of detoxification (mefenpyr-diethyl), suggest that iodosulfuron-methyl degradation is the mechanism involved on its selectivity to oat plants.

TOLERANCE OF COMMON BEAN PLANTS TO ETHOXYSULFURON HERBICIDE AND THE MECHANISM INVOLVED IN THE PROCESS

ABSTRACT The objectives of this study were to determine the effect of herbicide ethoxysulfuron on the development of commom bean (Phaseolus vulgaris), to evaluate the impact of the herbicide on the crop grain yield and to determine the mechanism of tolerance of common bean to ethoxysulfuron. Field experiments were carried out with several doses of ethoxysulfuron to determine its effect on the grain yield of two varieties of common bean ("IPR Andorinha", "IPR Tangará"). The mechanism of plant tolerance was evaluated through several methods, including the analysis of the ALS enzyme sensitivity to herbicide and the use of P450 inhibitors (the insecticides malathion + chlorpyrifos) and the use of antidote (mefenpyr-diethyl). When the rate of ethoxysulfuron was 83.2 g ha-1, the grain yield loss reached 25% (IPR Tangará) and 35% (IPR Andorinha). The ALS enzyme activity was severely reduced even at low concentrations ethoxysulfuron (1 μM), indicating that the mechanism of tolerance is not the insensitivity of the herbicide target enzyme. The inhibitors of herbicide detoxification increased the sensitivity of the bean plants to ethoxysulfuron, and the antidote (stimulator of herbicide degradation) mitigated the herbicidal effect. These results strongly support the hypothesis that the mechanism of tolerance of common bean plants to ethoxysulfuron is enhanced herbicide detoxification.

Detoxification of Herbicides in Phragmites australis

Unintentional loss of herbicides into drainage ditches, shores or other waterbodies may cause large problems in farmland. Therefore strategies for the phytoremediation of agrochemicals and especially herbicides have become a topic of great interest in many agricultural areas. However, in order to establish effective biological pollution control, information on the detoxification capacity of riparian plants and aquatic macrophytes (e.g., Phragmites australis) is important to build up effective buffer stripes. We determined the detoxification capacity of Phragmites australis roots and leaves for the conjugation of agrochemicals to glutathione by assaying the model substrate CDNB as well as the herbicides fenoxaprop-P, propachlor, pethoxamid and terbuthylazine. Specific GST activities were always higher in the rhizomes (6.78 d 0.88 μkat/mg protein for CDNB) than in leaves (1.08 d 0.21 μkat/mg protein). The detoxification capacity is distributed across an array of GST isoforms. In summary, Phragmites australis seems to be efficient in herbicide detoxification and a good candidate for phytoremediation of effluents from agricultural sites.