Effect of Sucrose and ABA on Survival Rate of Cryopreserved Protocorms of Dendrobium gratiosissimum Rchb.f.

Abstract

Dendrobium gratiosissimum Rchb.f. is a rare wild orchid. Cryopreservation is an alternative and important tool for ex situ preservation of orchid germplasm. In this study, protocorms of D. gratiosissimum were induced and cultured on solidified New Dogashima (ND) medium containing 0.3 mg/l NAA for two months. These protocorms were used as explants in cryopreservation using an encapsulation – dehydration method. For treatment with ABA, encapsulated protocorms were precultured in liquid ND medium containing various concentrations of ABA made up of 0, 0.01, 1 and 10 mg/l. For the sucrose treatment, beads were precultured in a semi-solid ND medium containing 0.25 M sucrose in the dark for one week at 4oC and then transferred into liquid ND medium containing 0, 0.5, 0.75 and 1 M of sucrose and then cultured for two days before dehydration. The highest percentage regrowth of cryopreserved explants was observed when precultured in the liquid ND medium supplemented with 1 mg/l ABA for one week and then dehydrated with silica gel in a laminar air-flow for five hours prior to immersion in liquid nitrogen for one hour. Regrowth ability testing performed after two weeks of treatment produced a rate of regrowth of 67% ± 0.5. Consequently, a simple and reliable protocol for the cryopreservation of D. gratiosissimum was clearly revealed in this study.