Survival and recovery of asparagus shoot tips after cryopreservation using the "droplet" method

In vitro cultured shoot tips of asparagus (Asparagus officinalis L.) were successfully cryopreserved using the "droplet" method. Excised shoot tips, pre-treated with liquid cryoprotective medium, were suspended in small droplets (c. 5 mul) of cryoprotectant on aluminium foil and then rapidly frozen by direct immersion in liquid nitrogen. Shoot tips of all eight asparagus genotypes tested were successfully cryopreserved, and within 7 days had resumed growth into well developed shoots (5-8 mm long) without intermediate callus formation. High survival and regrowth was achieved without any cold hardening or pre-growth, and ranged from 58% for clone M120 to 96% for cultivar 'Rutgers Beacon', with a mean frequency of c. 80% across all eight genotypes.