Regulatory effects of foliar sprays of plant growth regulators on endogenous hormones and carbon metabolism in alfalfa

This study aimed to clarify the effects of S-3307 and DA-6 on dynamic changes of endogenous hormones and carbon assimilates in alfalfa (Medicago sativa), and to provide a specific reference basis for the appropriate concentration of foliar applications of S-3307 and DA-6 for the high-yield cultivation method of alfalfa. The experiment was conducted to study the effects of foliar application of different concentrations of S-3307 (25, 50, 75 and 100 mg·L⁻¹) and DA-6 (20, 40, 60 and 80 mg·L⁻¹) on the shedding of alfalfa pods, and the endogenous hormone concentrations and carbon metabolism of blades and florets, using alfalfa of ‘Xinmu No.4’ as the test material. We found that the spraying of S-3307 and DA-6 had a significant regulatory effect, which could effectively increase the number of alfalfa florets and pods and reduce their abscission rate as the spraying concentration increased. The content of endogenous abscisic acid , zeatin riboside, and gibberellin in the blades and florets showed contrasting degrees of increase. Spray applications also promoted the accumulation of soluble sugar and starch in blades and florets. Compared with the control, S-3307 increased the sucrose content of leaves, which was conducive to improving the source-store relationship. In conclusion, foliar spraying with appropriate concentrations of S-3307 (75 mg·L⁻¹) and DA-6 (60 mg·L⁻¹) significantly increased the content of endogenous hormones and the metabolism of carbon assimilates in alfalfa and reduced the abscission rate of flowers and pods.