Objective In order to investigate the growth-regulating effect of the plant growth regulator brassinolide (BR) on seedlings of Flemingia philippinensis Merr. et Rolfe, and to establish the high efficient production technology system for floating–seedling-raising of F. philippinensis.

Method Using F. philippinensis seedlings as the experimental subject, four concentrations of BR (CK 0.000 mg/L, T1 0.010 mg/L, T2 0.015 mg/L, T3 0.020 mg/L) were applied via foliar spraying to investigate their regulatory effects on individual seedling growth performance indicators. A comprehensive evaluation of seedling growth traits was conducted using correlation analysis, principal component analysis, and the fuzzy membership function method.

Result The results indicated that there was no significant influence of the leaf numbers, the length of main root, the total volume of root and the mean diameter of root in F. philippinensis seedings among BR treatments, and the application of BR showed significant negative effect on decrease of main stem diameter of seedings. Compared with CK, the plant height, the number of base branches and the number of primary lateral roots treated with different BR concentrations increased significantly by 7.47%-20.21%, 272.3%-524.2% and 18.08%-24.60%, respectively. The dry matte weight per plant and the root-crown ratio increased significantly by 23.09%-25.97% and 18.38%-34.46%, respectively. The leaf area per plant, specific leaf weight and SPAD value increased significantly by 7.06%-30.15%, 4.19%-7.34% and 3.93%-4.37%, respectively, and the regulatory effect at a lower concentration (T1, T2) was particularly significant. The results of principal component analysis indicated that among the evaluation indicators of BR promoting the growth of individual seedlings, the variance contribution rate of agronomic traits of the aboveground part of the plant was the largest, at 53.10%; followed by leaf photosynthetic physiological factors (25.81%) and root morphology factors (21.08%). Through the comprehensive evaluation analysis of the membership function, it was known that the F values of different BR concentration treatments was T2 (0.782) > T1 (0.715) > T3 (0.268) > CK (0.210).

Conclusion Therefore, spraying BR (0.010-0.020 mg/L) could promote the growth and development of floating seedlings of F. philippinensis, and improve the quality and vigor of the seedlings, and the treatment of 0.015 mg/L BR by foliar spraying has the best effect.