Effects of Different Concentrations of Paclobutrazol Residue on Seedling Growth of Lettuce

Taking five lettuce cultivars as experiment materials, the method of simulating the residue of paclobutrazol in soil by mixing the paclobutrazol in plug substrate for seedling was used, and the concentrations of paclobutrazol（measured by active ingredients） were set with 7 residue levels of A1(0 mg·L^-1),A2(2.5 mg·L^-1),A3(5.0 mg·L^-1),A4(10.0 mg·L^-1),A5(20.0 mg·L^-1),A6(40.0 mg·L^-1) and A7(80.0 mg·L^-1).The effects of paclobutrazol residue on seedling quality, leaf types and the content of aboveground soluble solids of lettuce were studied, in order to explore the response mechanism of lettuce seedling growth to the paclobutrazol residual concentration.The results showed that with the increasing of the concentration of paclobutrazol, the plant height, fresh weight of the aerial parts, dry weight of the aerial parts, total leaf area, total leaf length, total leaf width, maximum functional leaf length, maximum functional leaf width and soluble solid of all cultivars were decreased, the SPAD value and root-shoot ratio were increased, while fresh root weight and dry root weight first were increased and then decreased.Among them, the plant height, fresh weight of the aerial parts, dry weight of the aerial parts, total leaf area and soluble solids of A5,A6 and A7 treatments were significantly lower than A1 treatment, and the SPAD value and root-shoot ratio were significantly higher than A1 treatment.With the increasing of paclobutrazol residue concentration in vegetable fields, the inhibition degree of growth and development in lettuce seedling stage was higher, and the inhibition effect reached significant level when paclobutrazol residue concentration was A5(20.0 mg·L^-1) and above.