Plant regrowth from potato shoot tips cryopreserved by a combined vitrification-droplet method

Shoot tips obtained from in vitro potato plants (three cultivars) were successfully cryopreserved by the combined vitrification-droplet method and subsequently regenerated shoots. The effect of apex size, sucrose concentration, preculture duration and cold hardening treatments on viability of cryopreserved shoot tips was studied. The excised shoot tips were incubated, precultured and dehydrated with concentrated PVS2 cryoprotective solution at room temperature, prior to a direct plunge in liquid nitrogen. After rapid rewarming in Murashige-Skoog (MS) liquid medium, shoot tips were plated on semisolid MS medium (3.5 g/l agar) supplemented with 0.4 mg l(-1) gibberellic acid, 0.5 mg l(-1) zeatin, 0.2 mg l(-1) indole-3-acetic acid and 30 g l(-1) sucrose for regrowth. Cryopreserved shoot tips resumed growth within 20 days and regenerated shoots within 30 days. The highest regrowth levels of apices after cryopreservation were 55% recovery for cv. Désirée, 51% for cv. Ostara and 46% for cv. Santé.