Plant availability and phytotoxicity of soil bound residues of herbicide ZJ0273, a novel acetolactate synthase potential inhibitor

The plant availability and phytotoxicity of soil bound residues (BR) of herbicide ZJ0273, a novel acetolactate synthase (ALS) potential inhibitor, to rice (Oryza sativa L.) and corn (Zea mays L) was investigated in three different soils including a Fluvio-marine yellow loamy soil (S-1), a Red clayey soil (S-2), and a Coastal saline Soil (S-3), using C-14-labeling tracer and bioassay techniques. When soils were amended with BR at 0.6. 1.2 and 1.8 nmol g(-1), dose-dependent and significant inhibition was observed for rice seedlings within 14 d after treatment, but no significant inhibition occurred to corn seedlings in the same treatment. Radioactive analysis of soil extracts following sequential extractions showed that the C-14 labeled residues of ZJ0273 were released from the amended soil BR upon planting. For example, when amended with 1.8 nmol g(-1), about 68.3%, 57.0%, and 61.1%, respectively, of the added BR were released in S-1, S-2, and S-3 planted with rice seedlings, whereas 38.9%, 32.7% and 32.6% became available for uptake in the corresponding soils planted with corn seedlings. The released compounds were identified as ZJ0273 and its degradation products M1 and M2, with M2 as the primary component. Bioassay on rice showed that concentration for 50% inhibition (IC50) of ZJ0273, M1, and M2 were 33.16, 1.93 and 0.49 mu M, respectively. Therefore, BR formed after application of ZJ0273 may become available for plant uptake during rice cultivation and lead to phytotoxic effects, and the phytotoxicity is mainly caused by the release of the biologically active metabolite M2. This knowledge is valuable for designing crop rotation practices so that crop injury and yield losses due to carry-over herbicide phytotoxicity may be avoided. (C) 2009 Elsevier Ltd. All rights reserved.