Differential Rooting Efficacy of Growth Regulators in <i>Camellia sinensis</i> Cuttings: A Physiological and Biochemical Analysis

The natural rooting rate and speed of cuttings of <i>Camellia sinensis</i> var. <i>Assamica</i> cv. <i>Hainan-dayezhong</i> (HD) are relatively low. To investigate the mechanisms by which growth regulators promote adventitious root (AR) formation in this tea variety, this study examined the effects of exogenous indene-naphthaleneacetic acid (ABT-1) and indole-3-butyric acid (IBA) treatments on the AR formation of cuttings, using water as a control. Systematic measurements and comparisons were carried out on the changes and differences in nutrient content, oxidase activity, and endogenous hormone levels and ratios during the AR formation process under the influence of exogenous hormone treatments. The relationships between these factors and the progression of AR formation in HD were analyzed. Both ABT-1 and IBA treatments significantly accelerated the AR formation process and improved the AR formation rate and AR formation index. Among them, IBA treatment showed a more pronounced promoting effect, increasing the AR formation rate by 21.58% and achieving an AR formation index of 32.14% compared with the control. During the AR formation process, both ABT-1 and IBA treatments increased the soluble sugar content and polyphenol oxidase (PPO) activity during the callus induction phase while decreasing peroxidase (POD) and indole-3-acetic acid oxidase (IAAO) activity during the callus induction and adventitious root initiation phases. Additionally, both treatments accelerated the consumption of endogenous hormones such as indole-3-acetic acid (IAA) and abscisic acid (ABA) and amplified fluctuations in cytokinin (CTK) levels and IAA/ABA ratios. Notably, IBA treatment resulted in greater changes in the soluble protein content and IAA/ABA ratio, with an increase of 49.22% and 80.87%, respectively. The two peaks of PPO activity occurred earlier, on days 10 and 40 after cutting, with IBA treatment having 6.85% and 40.35% higher activity than ABT-1 treatment at the corresponding time points, thereby maintaining relatively higher levels throughout callus induction and adventitious root initiation phases. Furthermore, IAAO activity decreased more significantly on days 10 and 30 after cutting, with decreases of 35.45% and 40.75%, respectively, which favored the formation of adventitious roots more. Both treatments promoted AR formation by regulating physiological balance, but IBA demonstrated superior efficacy in accelerating HD cutting rooting. These findings highlight IBA’s potential as a targeted growth regulator for improving HD propagation efficiency.