Abstract: This study explored the effects of gibberellin (GA₃) and 6-benzylaminoadenine (6-BA) plant growth regulator on the growth and endogenous hormone content of rhizome of Caucasian clover. Plant height, leaf number, chlorophyll and endogenous hormone contents (in above and below ground parts of Caucasian clover) were characterized under different concentrations of GA₃ (0 control, 300, 600, 900, and 1200 mg·L^-1) and 6-BA (0 control, 25, 50, 100 and 200 mg·L^-1). All GA₃ treatments dramatically increased plant height compared to the control (P<0.05). Under the 600 mg·L^-1 GA₃ treatment, mean plant height was 21.33 cm (4.12 times higher than the control treatment). Similar responses were seen at the other GA₃ concentrations(300, 900 and 1200 mg·L^-1). GA₃ also promoted the synthesis of chlorophyll a; the most significant treatment effect was a concentration of 0.92 mg·g^-1 (76.92% higher than the control treatment) found in the 600 mg·L^-1 GA₃ treatment (P<0.05). GA₃ had no significant effect on chlorophyll b content (P>0.05). Under 6-BA treatment, plant height was approximately 2.6 times that of the control treatment at all concentrations tested, and leaf number was more responsive than in the GA₃ treatments, being the highest (2.99 times higher than the control) at 200 mg·L^-1 concentration. 6-BA significantly promoted the accumulation of chlorophyll a and b (P<0.05). In general, endogenous hormone levels showed a dose response to exogenous hormone application across the concentrations tested. For the aboveground plant parts, exogenous GA₃ at 600 mg·L^-1 elicited increases in zeatin (ZT), GA₃ and auxin (IAA) of approximately 23.84%, 55.71% and 137.99%, respectively, and a decrease in abscisic acid (ABA) of approximately 44.09%; while exogenous 6-BA at 200 mg·L^-1 increased endogenous ZT, GA₃ and IAA levels by approximately 293.23%, 49.71% and 49.83%, respectively, and decreased ABA by approximately 52.48%, compared to control treatments. For the below ground plant parts, endogenous hormone responses were broadly similar to those in above ground parts, except that the ABA decrease from exogenous GA₃ (600 mg·L^-1) and 6-BA (200 mg·L^-1) application was much less (15.15% and 28.26%, respectively). In summary, 600 mg·L^-1 GA₃ and 200 mg·L^-1 6-BA are optimal concentrations for promotion of the growth and development of Caucasian clover.

Key words: Caucasian clover (Trifolium ambiguum), rhizome segment, GA₃, 6-BA, endogenous hormone