Routine cryopreservation of kiwifruit (Actinidia spp) germplasm by encapsulation-dehydration: Importance of plant growth regulators

The encapsulation-dehydration protocol was optimized for an in vitro cultur ed hybrid Actinidia arguta x A, deliciosa. Shoot tips from 14-d reactivated mononodal microcuttings were embedded, transferred to liquid culture mediu m whose sucrose concentration was daily increased (0.3, 0.5, 0.75 M) and th en kept at 0.75 M for 2 or 4 d. Dehydration on silica gel was monitored to 20+/-1.5% residual water content (dry weight basis), allowing direct quench ing in liquid nitrogen and rewarming at room temperature. Differential scan ning calorimetry analysis underlined the importance of reversible glass tra nsition in shoots for survival. Regrowth ranged from 85% to 95%. Growing sh oot tips showed no phenotypic abnormalities. Rooting was also achieved. Thi s method was routinely applied to diploid A. chinensis and A. eriantha, and to several diploid hybrids, yielding over 70% regrowth. A slight decrease in sucrose molarity (0.65 M) allowed tetraploid A. chinensis and A. chrysan tha x A. arguta to survive dehydration, but not quenching in LN. I;or A. de liciosa cv Hayward and cv Tomuri, normal regrowth after cryopreservation wa s achieved only after modification of the pre- and post-culture media, high lighting the importance of monitoring plant growth regulator balance, princ ipally at the post-thaw recovery step.