The objective of this study was to evaluate the feasibility of using 2-aminobutyric acid (2-aba) as a chemical marker for the detection of sulfonylurea (SU) herbicides in crop and soil environments. A bioassay, on the basis of the injury index to vegetable seedlings, showed that both field mustard and Chinese mustard were more sensitive to bensulfuron, imazosulfuron, and pyrazosulfuron than lettuce and cabbage in winter. In a similar study, field mustard was found to be the most sensitive species among six summer vegetables. After foliar application of bensulfuron at 0.487 μM, 2-aba accumulation reached the maximum in field mustard within 6 to 12 h, before any visible symptoms appeared, and this high level was maintained up to 72 h. Among all vegetables tested for differential SU sensitivities, maximum accumulation of 2-aba occurred, in coincidence with the onset of injury, in field mustard. The accumulation of 2-aba in field mustard showed a linear regression to the log-transformed concentrations, ranging from 10−2 to 102 μM, of each of the three SUs. However, no such relationship between the applied rate, especially at the lower rates, and the residue content of SUs in field mustard plant was found. In addition, with the extract of SU-treated paddy soil sprayed on field mustard, the accumulation of 2-aba in this plant was found to reflect indirectly the amount of SU residues in the soil.
Nomenclature: 2-aminobutyric acid; bensulfuron; imazosulfuron, 1-(2-chlorimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxy-pyrimidin; pyzazosulfuron; cabbage, Brassica oleracea L. var. ‘Capitata’; Chinese mustard, Brassica rapa L.; field mustard, Brassica campestris L.; lettuce, Lactuca sativa L.; rice, Oryza sativa L.
Additional index words: Bensulfuron, bioassay, imazosulfuron, pyrazosulfuron.
Abbreviations: 2-aba, 2-aminobutyric acid; ALS, acetolactate synthase (EC 18.104.22.168); DAT, days after treatment; FW, fresh weight; HAT, hours after treatment; HPLC, high-performance liquid chromatography; SUs, sulfonylureas; TLC, thin-layer chromatography.