Regeneration of Dioscorea floribunda plants from cryopreserved encapsulated shoot tips: effect of plant growth regulators.

The encapsulation-dehydration protocol for the cryopreservation of in vitro shoot tips of Dioscorea floribunda was optimized. Maximum survival of 87% was obtained when overnight pretreatment with 0.3 M sucrose was followed by encapsulation, preculture in 0.75 M sucrose for 4 d, dehydration in a laminar air flow for 51/2 h, quenching in liquid nitrogen and thawing at 40°C. During recovery growth, 29% shoot formation was obtained when cryopreserved shoot tips were initially cultured for 25 d on a medium with 1.5 mg l -1 BAP, 0.2 mg l -1 NAA and 0.2 mg l -1 GA 3 followed by culturing for 15 d on a medium with reduced BAP (1 mg l -1 ) but increased NAA (0.5 mg l -1 ) and GA 3 (0.3 mg l -1 ). Finally, transfer on to a medium with further reduced doses of BAP (0.05 mg l -1 ) and NAA (0.15mg l -1 ) but without GA 3 stimulated production of fully grown plantlets. All plants regenerated without callus formation. Modification of post-thaw culture media with plant growth regulators was essential for regrowth of shoot tips to plantlets.