Identification And Degradation Characteristics Of A Quinclorac-degradate Bacterium

Quinclorac is a highly selective auxin herbicide, characterized by safety to rice, and primarily for control of Echinochloa spp. It is widely used in agricultural production. Meanwhile, it is highly stable, and degradation in nature is very slow. The quinclorac residues are phytotoxic to the tobacco in the rice-tobacco rotation field. Therefore, the study on monitor levels of Quinclorac residue and bioremediation is of vital importance for reducing the quinclorac phytotoxicity to the tobacco and protecting environment.1. In this paper, a method for determination of quinclorac in water by high-performance liquid chromatography in laboratory was proposed. The correlation coefficient was 0.9999 in the ranges of 0.1mg/L～10mg/L. The average recoveries of quinclorac ranged 95.7%～103.8% and the relative standard deviation was lower than 7% when the added concentration of quinclorac was 1.0mg/L to 20mg/L. The result indicated that the method had higher linearity, precision, accuracy and used less timen. Hence, the method would be valuable for the determination the quinclorac and its preparation in water.2. A quinclorac degradation bacterium named as YN5 was isolated from rice field with long-term usage of quinclorac in Jiangle Town, Wanan Town and laboratory in FAFU. Based on the morphological characteristics and 16SrDNA sequence analysis, YN5 was identified as Pseudomonas brassicacearum. The growth and degradation characteristics of YN5 were studied by investigating the effects of incubating time, temperature, pH values, inoculation size and initial concentration of quinclorac. The results showed that YN5 could grow when the temperature ranged from 25 ℃ to 35℃ and the pH values was from 6 to 8. The optimal value of temperature, pH values, inoculation size were 28 ℃,7.1 and 6% respectively. Under the optimal degrading condition, the strain YN5 could degrade 40% above of quinclorac from the initial concentration of 10mg/L in 5 days.3. The quinclorac concentrations of 0.0mg/kg,0.005mg/kg, 0.01mg/kg, 0.02mg/kg,0.03 mg/kg, and 0.04 mg/kg were added to the pot cultivation of tobacco. Afer 30 days, the leaf length, leaf width and the plant height of tobacco were significantly inhibited with the quinclorac of 0.01mg/kg, and the quinclorac phytotoxicity was more serious when the quinclorac concentration was beyond O.Olmg/kg. The inhibiton of leaf width was stronger than of leaf length and plant height. On the other hand, to examine the potential usage of YN5 as a bioremediation for quinclorac phytotoxicity, the 1OmL/kg of YN5 culture medium were added to the tobacco with 0.04 mg/kg of quinclorac. The results showed that the leaf width of tobacoo recoved to 40% of the growth rate for those in the control group. The pot experiment suggested that strain YN5 may be capable of bioremediation of quinclorac phytotoxicity. The study would be valuable for the pratical applications.