عنوان مقاله [English]
Introduction: Sethoxydim is a post emergence graminicidethatcontrolannual and perennial grasses such as wild oat (Avena ludoviciana Durieu.) and littleseed canarygrass (Phalaris minor Retz.) by inhibitory activity on acetyl coenzyme A carboxylase enzyme and disrupt fatty acid biosynthesis. It belongs to the cyclohexanone chemical family. It was registered for weed management in broad leaf crops. Using an adjuvant (e.g. vegetable oils and surfactants) that can increase the foliar activity of post emergence herbicides by cuticle destruction and increase leaf wetting is an acceptable way to achieve this approach. Applying vegetable oils increased graminicide penetrate to leaf and post emergence herbicides performance. Some synthetic adjuvants have been shown a side effect on wildlife, similar to agrochemicals therefore using safe and reproducible adjuvants is essential. The objective of this research is to determine the best vegetable oil on biological activity of sethoxydim on wild oat and relation between compounds of vegetable oils (fatty acids) and their effects on sethoxydim performance.
Materials and Methods: The dose response experiment was conducted in Research Greenhouse of Ferdowsi University of Mashhad in 2012. The seeds of wild oat were collected from plants in the fields of the Mashhad Agricultural and Natural Resources Research Center, in Mashhad, Iran and preserved at room temperature in paper bag. The seeds were surface sterilized by immersing in sodium hypochlorite for 5 minutes. Then seeds were rinsed by distilled water for 15 minutes. To increase seed germination before the start of experiment, the seeds were dehulled and placed in Petri dishes on top of a single layer of Whatman no. 1 filter paper. Then, 10 mL of 0.2% KNO3 solution were added to each Petri dish for breaking dormancy, then the seeds were incubated for 72 h at 4–5◦C in the dark. The germinated seeds were sown in pot (1.5 L). One week after sowing plants were tinned to four plant in each pot. The pots were irrigated every days. At four leaf stage of wild oat plants the herbicide treatment were applied. The treatments included sethoxydim concentration at seven levels (0, 23.4, 46.8, 93.75, 187.5, 281.25 and 375 g ai ha-1 of sethoxydim) and vegetable oils at ten levels (without oil and with turnip, olive, soybean, corn, sunflower, canola, sesame, castor, and cotton oil). The response of wild oat biomass were analyzed by non-linear regression by R software. To determine toxicity of sethoxydim plus vegetable oils on sugar beet and onion an experiment by recommended dose of sethoxydim was conducted. Moreover, an experiment was carried out to determine the fatty acid content and quantity of each vegetable oil. To determine the chemical nature of fatty acid oils, 15 drops of each vegetable oil were added to 7 mL N-hexane plus 2 mL of potassium hydroxide in methanol (11.2% m/v). Then, four replications of the supplied compounds were shacked for 1 min and heated to 55°C for 5 min until the solution was separated into two phases. The upper phase was desiccated with sodium lauryl sulfate and filtered to analyze with gas chromatography. The fatty acid content was determined using gas chromatography Acme 6000 (Younglin, South Korea) equipped with a flame ionization detector and a CP-Sil 88 Wcot fused silica column (100 m × 0.25 mm i.d. × 0.2 μm film thickness; Chrompack, Middleburg, Netherlands). The carrier gas was ultrahigh-purity helium; we used a 1:100 split mode and a flame-ionization detector. The GC oven temperature was maintained at 140 °C for 5 min, then ramped to 240°C at the rate of 4°C/min and maintained at 240°C for 15 min. The flow rate of helium was 20 mL/min. The injector and detector temperatures were 250 and 280°C, respectively. The volume of injected sample was 1 μL. Fatty acids were identified by matching their retention times with those of their relative standards.
Results and Discussion: Results of this study showed that sethoxydim performance improved in the presence of vegetable oils whereas relative potency were higher than 1 in the presence of vegetable oils compared to sethoxydim alone. The vegetable oil could be ranked based on their relative potency value as: turnip > olive > soybean > corn > sunflower > canola > sesame > castor > cotton. The overall results showed that the efficacy of sethoxydim was improved by increasing the content of unsaturated fatty acids in vegetable oils. Turnip and cottonseed oils with 71.17 and 20.65 percentages of unsaturated fatty acids had the highest and lowest performance, respectively. Among the polyunsaturated fatty acids compounds, linoleic acid content had a key role in the efficiency. There was a negative relationship between linoleic acid content and the performance of vegetable oils. Moreover, non-significant toxicity effects on sugar beet and onion was observed.
Conclusion: Based on this work, when the vegetable oils used the performance of sethoxydim on wild oat control based on relative potency were improved. Therefore, synthetic adjuvants can be replaced by vegetable oils as adjuvants in herbicide application. Based on results of this work, composition of fatty acids in vegetable oil is a very effective factors for increasing sethoxydim performance on wild oat control. By increasing unsaturated fatty acids, the sethoxydim performance showed more performance whereas turnip oil with higher unsaturated fatty acids was showed the highest performance. Further research is needed to determine the mechanism of action of vegetable oils in increasing the effectiveness of herbicides.