Regulating Growth of Betula alnoides Buch. Ham. ex D. Don Seedlings with Combined Application of Paclobutrazol and Gibberellin

Abstract

The rainy seasons have been becoming irregular and unpredictable under global warming now. This usually makes seedling preparation more difficult to match transplanting. Here applications of plant growth regulators, paclobutrazol (PBZ) and gibberellins (GA3) were studied with two trials to regulate growth of Betula alnoides Buch. Ham. ex D. Don container seedlings for the purpose of improving their quality when transplanting delayed. In the first trial five treatments (coded as P1 to P5) were laid out with total dosages of 0 mg (control), 2 mg, 6 mg, 10 mg and 20 mg PBZ per seedling to assess inhibitory effects of PBZ on growth of B. alnoides seedlings. After four and a half months, the second trial was carried out on the seedlings from the optimized PBZ treatments to detect growth recover of the seedlings by GA3, in which four treatments were arranged with GA3 dosages being 0, 1/10, 1/5 and 1/3 of the optimized paclobutrazol amounts applied. PBZ applications resulted in a significant decrease of height and root collar diameter growth since approximately one and two months after being treated, respectively. Among these treatments, P5 was the best one in controlling seedling growth, and its inhibitory effects lasted more than four and half months. PBZ treatments differed obviously in total seedling biomass from the control at 96 and 132 days after treatment (dat), and allocated more ratio of biomass into roots. Their root/shoot ratios increased and leaf areas decreased considerably with increasing PBZ dosage, while only P5-treated seedlings showed remarkable difference from the control in chlorophyll contents. The GA3 recovery showed that 15-day height increments of seedlings treated with GA3 were twice more than that without GA3 treatment, and did not differ significantly from the control without PBZ and GA3 treatment. It is concluded that the combined application of PBZ and GA3 can be recommended as a potential tool for regulating growth of B. alnoides seedlings, making it flexible to growing seedlings in the nursery.