Effects of spraying stages of paclobutrazol on seed setting characteristics of Chinese milk vetch (Astragalus sinicus L.)

Objectives The effect of applying paclobutrazol at different stages were compared through seed setting characteristic of Chinese milk vetch, in expectation of providing references for improving yield through use of chemical regulation.

Methods A Chinese milk vetch cultivar ‘Xinzi No.1’” was used in a field experiment. Five foliar application stage treatments were setup, including late wintering (T₁), returning green (T₂), squaring (T₃), pre-flowering (T₄), and 5 days after-flowering (T₅), and foliar spraying water was used as control (CK). During the flowering stage, the morphological and quantitative characteristics of flowers and pod setting at the basal, central, and apical inflorescences were investigated. At harvest, the number of pod, seed and seed weight at the three inflorescences, and the yield and yield components were determined using conventional methods.

Results The number of flowers, pods and seeds, and the setting rates of pods and seeds at bottom, central and apical inflorescences in all the spraying stage treatments, except in squaring stage, did not differ significantly from those in the control. When sprayed at the squaring stage, the seed yield was the highest, and was 32.3% higher than control. Under the spraying stage, the number of flowers, pods, seeds and the pod and seed setting rates in the basal inflorescences were increased by 20.4%, 31.4%, 23.9%, 5.25% and 2.38%, and by 12.3%, 32.9%, 22.8%, 7.42% and 2.08% in the central inflorescences, and by 18.4%, 54.8%, 70.9%, 2.56% and 3.78% in the apical inflorescences, respectively, compared with the control. The seed weights at the three inflorescences did not differ significantly with those of the control.

Conclusions Foliar application of paclobutrazol at squaring stage is effective in promoting the flower development, reducing the shedding, and benefit the setting of pods and seeds, especially in the basal and central inflorescences, and result in high seed yield at last. Foliar spraying paclobutrazol before and after squaring stage will not have the promotion effect.