Acclimatization of Dendranthema zawadskii Tzvelev by Using in Vitro Paclobutrazol Pretreatment

An efficient and labor-saving acclimatization method of Dendranthema zawadskii was developed using in vitro paclobutrazol (PBZ) pretreatments. Shoot tip cultures of five D. zawadskii taxa for in vitro rooting were performed on MS media containing various concentrations of PBZ alone. The PBZ at 1.7 μM in all taxa showed the heaviest fresh weight and vigorous growth of in vitro plantlets. Six outdoor acclimatizing methods on D. zawadskii ssp. coreanum consisted of the combinations of three starting materials and two humidity control conditions. Three starting materials were compact in vitro shoots, normal plantlets and compact plantlets. Two humidity control conditions were divided by the presence of wrapping treatment with a transparent film to retain moisture when each starting material was transferred to a greenhouse. Compact in vitro shoots and normal plantlets acclimatized without wrapping died due to severe wilting under greenhouse. Thus, only four acclimatization methods were comparable. All plantlets except compact in vitro shoots showed a 100% survival rate at 21 d after transplantation to greenhouse. Though humidity control such as a wrapping process was necessary to acclimatization of such plantlets, compact plantlets derived from in vitro PBZ pretreatment did not require wrapping for survival and growth. It can be suggested that in vitro PBZ pretreatment is an easy and simple acclimatizing method of in vitro plantlet without humidity control. Also, this simple acclimatization method was employed to acclimatize five taxa of D. zawadskii plantlets. All taxa showed successful acclimatization and well-developed rhizomes at 63 d after transferring to glasshouse condition.