ARS | Publication request: Cold Acclimation Improves Regrowth of Cryopreserved Apple Shoot Tips

Submitted to: CryoLetters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 2008
Publication Date: N/A

Interpretive Summary: Cryopreservation of diverse types of apples is important for Kazakhstan, the center of origin for apples. We compared five apple cultivars for cold hardiness and the ability to withstand cold temperatures and to recover from storage in liquid nitrogen (cryopreservation). Apple shoot tips were cold acclimated with short warm days and long cold nights for 0 to 6 weeks and cryopreserved by two common techniques. Cold hardiness of non-acclimated tissue culture plants ranged from -6.5 °C to -9.2 °C and these results are similar to the reported cold hardiness of field grown plants. Tissue culture plantlets that were both cold acclimated to withstand -12 °C to -15 °C and then cryopreserved had 50 to 80% regrowth for all genotypes tested. The non acclimated plants had only 10-12% regrowth after cryopreservation. The response of plants to the two techniques was similar for regrowth of shoot tips at each cold acclimation period. Overall 2 to 5 weeks cold acclimation produced significantly higher regrowth for each of the five cultivars. Despite the differences among the types of apples, 3 weeks of cold acclimation can be recommended as a standard protocol prior to apple cryopreservation. These conditions resulted in moderate to high recovery for all the apples tested and both cryopreservation methods used.

Technical Abstract: Cryopreservation is important for preserving the genetic resources of apple germplasm in Kazakhstan, the center of origin for apples. In this study of five apple genotypes [Malus domestica Borkh. and Malus sieversii (Ledeb.) M. Roem] we determined cold hardiness and the effect of cold acclimation on shoot tip recovery following cryopreservation by two popular techniques. Apple shoot tips were cold acclimated (CA) for 0 to 6 weeks and cryopreserved using PVS2-vitrification and encapsulation-dehydration techniques. Cold hardiness was indicated by LT50s and for non-acclimated shoots ranged from -6.7 °C to -9.3 °C. These LT50s resembled the natural cold hardiness of field grown plants and resulted in 10-12% regrowth after cryopreservation. Acclimated plantlets had LT50s of -12 °C to -15°C after 1 to 3 weeks CA, and following 3 weeks CA cryopreservation shoots averaged 65% regrowth. There were no significant differences between the two techniques for regrowth of shoot tips at each cold acclimation period. Overall, 2 to 5 weeks of cold acclimation produced high regrowth for each of the five cultivars. Three weeks of alternating temperature cold acclimation can be recommended as a standard protocol for Malus germplasm cryopreservation. These conditions resulted in moderate (60%) to high (80%) recovery for all genotypes tested and both cryopreservation methods used.