Effects of chlormequat chloride and paclobutrazol on growth and development and seed setting characteristics of Chinese milk vetch (Astragalus sinicus L.)

Objectives This study explored the influences of foliar spraying of chlormequat chloride (CCC) and paclobutrazol on growth and seed setting of Chinese milk vetch, to screen the appropriate spraying stage and provide an effective way of increasing yield through chemical control.

Methods The used Chinese milk vetch cultivar in a field experiment was ‘Xinzi1’. The two growth retardants were foliar sprayed separately in five stages: late wintering, returning green, squaring, pre-flowering and 5 days after-flowering, water was sprayed at the same time which was recorded as control. The concentrations of CCC and paclobutrazol were both 400 mg/kg. We investigated the plant heights, stem diameters, branch numbers, SPAD values and weight per plant at full-flowering stage, and the number of flowers, pods, seeds, pod set rates and seed set rates on the main stems at mature stage.

Results Foliar spray of both CCC and paclobutrazol at the squaring stage significantly inhibited plant height, but significantly increased branch numbers, SPAD value and weight per plant, and paclobutrazol performed better than CCC did. Compared with spraying water (control), the number of flowers, pods, seeds, pod set rates and seed set rates were increased by 16.32%, 21.45%, 15.94%, 2.38 percentage points and 0.94 percentage points when praying CCC at squaring stage, while significantly decreased when spraying at late wintering and returning green stages; the number of flowers, pods, seeds, pod set rates and seed set rates were increased by 31.69%, 43.41%, 29.49%, 4.76 percentage points and 2.14 percentage points when spraying paclobutrazol at squaring stage, but flower number and pod seed set rate were significantly decreased when spraying at late wintering stage. The highest seed yields were obtained when spraying CCC and paclobutrazol at squaring stage, with the increment of 15.95% and 29.88% than control.

Conclusions Foliar application of paclobutrazol and chlormequat chloride at squaring stage could effectively control the plant height, reduce the shedding, and promote seed setting characteristics, as a result, achieve higher seed yield. Paclobutrazol is proved of better chemical control and promotion effect than chlormequat chloride.