Improved survival after cryogenic exposure of shoot tips derived from in vitro plantlet cultures of potato.

In vitro plantlets were used for axillary shoot tip isolation to avoid microbial contamination which often occurred from use of greenhouse-grown plants. Periodic subculturing gave a supply of uniform plantlets necessary for obtaining shoot tips for cryogenic experiments. Previous results have shown that all cells within a shoot tip did not survive cryogenic exposure and the regrowth percentage depended upon the composition of the culture medium. A medium containing 0.5 mg/liter zeatin, 0.2 mg/liter gibberellic acid, and 0.5 mg/liter indoleacetic acid gave regeneration of a multiple-shoot mass from control and some frozen shoot tips. The two-step cooling procedure (0.2-03 degrees C/min to -35 degrees C followed by immersion in liquid nitrogen) gave high percentages of regrowth in the cultivars Norland and Red Pontiac. Shoots were obtained from treated materials in both cultivars.