Objective Effects of applying plant growth regulator, 2% 28-homobrassinolide·benzylaminopurine (28-HBR·BAP), on the growth and biochemistry of tea bushes were studied.

Method A randomized complete block design using water as blank control (CK) and 3 reference agents, including 2% 28-homobrassinolide (28-HBR) aqueous solution at the rate of 0.02 g a.i.·hm⁻², 2% benzylaminopurine (BAP) soluble concentrate at 10 g a.i.·hm⁻², and 0.136% GA₃·IAA·BR wettable powder at 0.102 g a.i.·hm⁻², 28-HBR·BAP soluble concentrate at the rate of 6, 7.5, 10, and 15 g a.i.·hm⁻² were applied on the lots for the field experimentation. Leaves and buds were plucked from the tea bushes on April 16, April 26, and May 6 to determine the bud density, hundred-bud weight, and fresh leaf yield, as well as the contents of tea polyphenols, caffeine, and total free amino acids.

Result The 2% 28-HBR·BAP application significantly stimulated the bud sprouting on the plants. At the rate of 15 g a.i.·hm⁻², increases over CK of 4.37%-17.88% on bud density, 9.07%-17.99% on hundred-bud weight, and 13.98% on average fresh leaf yield were observed. Biochemically, the increasing dosage significantly raised the contents of tea polyphenol from 13.45% to 15.30%, caffeine from 4.20% to 5.63%, and polyphenol-amino acid ratio from 5.51 to 7.59, except total free amino acid, in comparison to CK and 3 reference agents refered above.

Conclusion A significant growth promoting effect with increased fresh leaf yield and elevated tea polyphenols and caffeine contents on the tea bushes were observed by the application of 2% 28-HBR·BAP.