Improvement of the tolerance of Perilla frutescens (L.) Britt. seedlings to clethodim stress by urea

The effects of urea and clethodim on the growth, photosynthetic characteristic, resistance, weed control and yield of Perilla frutescens (L.) Britt. were studied by using the randomized block design experiment. Perilla frutescens (L.) Britt. seedlings at the six-leaf stage were treated with either different concentrations of urea (0, 1, 2, 4 and 8 g/L) or 24% clethodim EC (0, 0.67, 1.33, 2.66 and 3.99 mL/L) or their combinations. The results show that the seedling growth and photosynthetic characteristic are depressed, while the accumulation of malondialdehyde (MDA) is increased under the clethodim treatments. The activities of superoxide dismutase (SOD) and peroxidase (POD) are increased at first, and then decreased with the increase of clethodim level. The seedling growth and photosynthetic characteristic are improved under lower dosages of urea (14 g/L), but depressed under higher concentration of urea (8 g/L). Pre- and post-treatments with lower dosages of urea (14 g/L) and different concentrations of clethodim show better effects than the clethodim treatment without urea.Compared with the application of clethodim alone, the dry weight at the squaring stage, seed yield and weed control efficiency are increased as by 13.94 %, 10.54 % and 11 %, respectively under the application of 4 g/L urea in combination of later application of 0.67 mL/L clethodim. These results indicate that Perilla frutescens (L.) Britt. seedling tolerance to clethodim stress is increased effectively. The growth and net photosynthetic rate (Pn) are improved through the increase of antioxidant enzymes when treated by 4 g/L urea first and then by 0.67 mL/L clethodim. This combination of urea and clethodium could improve the weed control effect, promote Perilla frutescens (L.) Britt. seedling growth and crop production, and exhibit great potentials for practical application.