Effects of Chlormequat Chloride and Paclobutrazol on the Growth and Chlorophyll Fluorescence Kinetics of Daphne genkwa

Daphne genkwa has high ornamental value, strong resistance and medicinal value, but its leggy ability is not conducive to cultivation management. In this study, different concentrations of chlormequat chloride (CCC, 200, 600, 1800, and 5400 mg/L) and paclobutrazol (PP333, 500, 1000, 2000 and 4000 mg/L) were sprayed three times on 2-year-old D. genkwa. The dwarfing mechanism of retardants was analyzed from leaf spectral reflectance and chlorophyll fluorescence kinetics. The results showed that a higher retardant concentration resulted in significant dwarf growth. The higher retardant concentration, the shorter flower branches, and the smaller flower area, except for 2000 mg/L PP333 treatment. Relative contents of leaf pigments maintained a stable high level after the third spraying of retardants (CV < 13.2%). In the near-ultraviolet region, reflection spectral intensity with the PP333 application was higher than CCC, but both were significantly higher than the control. The kinetic curve of fast chlorophyll a fluorescence induction showed that the performance in fluorescence intensity with PP333 treatment was better than that of CCC. With spraying increased, the number of reaction centers (RC/CSm) and the capacity of PSII (S-m) significantly increased, resulting in improving the ability of electronic transmission from PSII to PSI (& psi;(o) and & phi;(Ro)). Finally, the maximal photochemical efficiency of PSII (F-v/F-m) and performance indexes (PIabs) significantly increased. In conclusion, retardant treatments could promote plant dwarfing and reproductive growth by improving the ability to resist ultraviolet light and photosynthetic efficiency. 2000 mg/L PP333 sprayed three times had the best performance.