Routine cryopreservation of kiwifruit (Actinidia spp) germplasm by encapsulation-dehydration: importance of plant...

The encapsulation-dehydration protocol was optimized for an in vitro cultured hybrid Actinidia arguta x A. deliciosa. Shoot tips from 14-d reactivated mononodal microcuttings were embedded, transferred to liquid culture medium whose sucrose concentration was daily increased (0.3, 0.5, 0.75 M) and then 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 quenching in liquid nitrogen and rewarming at room temperature. Differential scanning calorimetry analysis underlined the importance of reversible glass transition in shoots for survival. Regrowth ranged from 85% to 95%. Growing shoot tips showed no phenotypic abnormalities. Rooting was also achieved. This 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. chrysantha x A. arguta to survive dehydration, but not quenching in LN. For A. deliciosa cv Hayward and cv Tomuri, normal regrowth after cryopreservation was achieved only after modification of the pre- and post-culture media, highlighting the importance of monitoring plant growth regulator balance, principally at the post-thaw recovery step.