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The objective of this work was to determine the coefficients of ametryn sorption and desorption in Red-Yellow Ultisol (PVA) and Red-Yellow Latosol (LVA) with different pH values. Thus, 0-20 cm depth soil samples were collected from degraded pastures without the use of herbicide in the region of Viçosa-MG, and incubated or not with limestone for 90 days. The Batch slurry method was used under controlled laboratory conditions. The method consisted of using 10.0 mL solution at increasing concentrations of ametryn standard, prepared in 0.01 mol L -1 CaCl 2 solution, added to 2.00 g of soil, and remaining under rotating agitation for 12 h (pre-determined equilibrium time). After centrifugation and filtration, the supernatant concentration was determined by high performance liquid chromatography (HPLC) with UV detector of 245 nm. Desorption was evaluated using the samples contained in the tubes, after the sorption trials, which contained the initial dose of 25 mg L -1 of herbicide. The PVA presented the highest adsorption coefficient (K fa) compared to the LVA,regardless of the pH values of the samples. This was attributed to the higher organic matter content in the PVA, compared to the LVA. When comparing the same soil (LVA) at different pH values, it was observed that pH value increase resulted in a lower K fa value. Low hysteresis indices were observed for ametryn in the soils studied, representing a risk of this herbicide leaching in the profile of these soils.


Arejao E.V.V.,Federal University of Viçosa | Demuner A.J.,DEQ UFV | Barbosa L.C.A.,DEQ UFV | Barreto R.W.,Dep. de Fitopatologia | Vieira B.S.,Federal University of Uberlandia
Planta Daninha | Year: 2013

The fungal species Alternaria euphorbiicola was identified as causal agent of inflorescence necrosis, leaf blight, and stem cancer in Euphorbia heterophylla (wild poinsettia), a major weed responsible for great agricultural losses in Brazil. The application of spore suspensions of the fungus on specimens of the host plant resulted in production of disseminated necrosis at short time intervals (24 to 48 hours) after application. These observations led to the hypothesis that the fungus could produce phytotoxins capable of causing damage to the plant. The objective of this study was to investigate the in vitro production of phytotoxins by A. euphorbiicola under different growth conditions. The results showed that the culture medium and growth conditions influenced the phytotoxicity of the culture filtrates. Growing the fungus under agitation in the dark resulted in higher production of phytotoxic metabolites. The filtrate from the culture formed in modified Jenkins-Prior medium, under agitation, at 28 °C in the dark showed the highest phytotoxic activity. This filtrate produced foliar necrosis and defoliation in E. heterophylla and was subjected to extraction followed by bioassay-guided fractionation. A chromatographic fraction consisting mainly of long-chain fatty acids produced bleached lesions and necrosis of the leaves, the same symptoms observed after inoculation of the fungus in the host plant. These results suggest the involvement of these phytotoxic fatty acids in the process of tissue invasion of E. heterophylla by A. euphorbiicola.

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