Effect of quizalofop on protective enzymes and photosynthesis in Radix Isatidis

The experiment was aimed to study the effect of Quizalofop on Radix Isatidis (RI) and its response mechanisms, and select a safe and efficient type and concentration of herbicide. With the help of random block methodology to figure out the different doses of Quizalofop effect after spraying, the pattern of the concentration of some protective enzymes were identified, and some photosynthetic characteristics were also measured. Results showed that under different concentrations of Quizalofop treatment, many enzyme activities were changed in response to the time length. The photosynthesis progress of Radix Isatidis was slightly impacted at a low dose. Malondialdehyde (MDA) of Isatis leaf got injured more by Quizalofop when the dose increased. The effect of Quizalofop on the RI leaves was changing with the time after spraying, which showed a trend of declining after increasing. In conclusion, Quizalofop with a low dosage of 225-450 ml/hm2 may affect RI photosynthesis slightly and can be used safely. Key words: Radix Isatidis, quizalofop, protective enzymes and photosynthesis.