The present status of butachlor resistance to Echinochlor crus-galli (L.) Beauv. (CE) occurring in paddy rice in north and south of China was studied. With continuing application of butachlor in the fields of Hubei and Heilongjiang Provinces, it was noticed that the herbicidal efficacy for controlling EC was reduced. Seeds of different EC populations collected from 6 sites (Yueyang, no butachlor applied, Team Ⅲ on Zhanghuyuan Farm with 14-year application of butachlor, Team Ⅳ on Zhanghuyuan Farm with 18-year application of butachlor in the south; Mudanjiang, no butachlor applied, Minzhu with 10-year application of butachlor, Acheng with 14-year application of butachlor in the north) were tested to evaluate butachlor-resistant status in the areas. It was revealed that LC_(50) for controlling of Yueyang population was the lowest, while that of Mudanjiang population was the highest among six populations, 54.73 g a.i. ha~(-1) and 1271.6 g a.i. ha~(-1) respectively. The order of sensitivity of the populations from high to low ranged: Yueyang, Acheng, Team Ⅲ, Minzhu, Team Ⅳ, Mudanjiang. As the control of Yueyang population, RI indexes of other populations excluding Mudanjiang population were Acheng 5.21, Team Ⅲ 5.85, Minzhu 8.00, Team Ⅳ 12.01, which indicated that the four populations had evolved resistance to bubachlor. Biochemical tests showed that when the seedlings of EC were treated with butachlor (5 ppm) for 48 hours, GSTs activities increased, the amount of GSH showed significant difference. The seedlings of EC were treated with butachlor (5ppm) for 9 days, compared to the untreated populations, the GSTs (CDNB) activities of each treated population were higher with exception of Acheng population, but the amount of free thiols, such as GSH and Cysteine varied according to different populations. GSTs activity of the untreated seedlings grown for 14days showed positive correlation to LC_(50) for controlling of the populations in the south, but negative correlation to LC_(50) of those in the north. The free thiols and GSTs activities to CDNB in EC populations indicated that butachlor resistance in EC was not increased notably. GSTs activity or the amount of GSH did not show direct correlation with the LC_(50) for controlling of different populations. It is suggested that the analysis method needs to be improved, study of other possible mechanism is needed.
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