Post-Thaw Survival of Meristems from In Vitro Sweet Potato (Ipomoea batatas (L.) Lam.) Plants ^†

Cryotherapy of shoot tips can effectively eliminate the sweet potatoes pathogens, such as viruses and phytoplasm, and is impossible without the development of effective cryopreservation techniques. At the same time, cryopreservation allows a long-term germplasm storage. In this study, we developed and compared different methods for sweet potatoes’ meristems treatment for optimized preservation. The meristems of Admiral variety up to 1–2 mm were isolated from in vitro growth plants. In one group the specimens were dehydrated for 120 min with sterile air flow and immersed into liquid nitrogen at a needle tip. The meristems of other groups were dehydrated with plant vitrification solutions (modified PVS 1, PVS 2, 88% PVS 3, and PVS N). The samples were immersed into liquid nitrogen either in 1.8 mL cryovials or 50 µL hermetically sealed aluminum pans for differential scanning calorimetry. It was shown that the survival rates of meristems were 55% after 88% PVS 3 treatment and 83 and 85% after PVS 2 and PVS N exposure. The highest percentage of preserved specimens was found after dehydration with air-flow and modified PVS 1 (89–95%). After cryopreservation in 1.8 mL cryovials the highest post-thaw preservation was noted after pretreatment with modified PVS 1 (60–75%) and the lowest one was observed with 88% PVS 3 (35–40%). Meristems treated with PVS 2 and PVS N provided 45–55% survival rates. After cryopreservation in aluminum pans the highest post-thaw preservation was detected for dehydration with modified PVS 1 (81–84%) and the lowest one was found with 88% PVS 3 (40–51%). Meristems treated with PVS 2 and PVS N revealed of 68–78% post-thaw survival respectively. The meristems cryopreservation method based on dehydration with sterile air flow is of special interest, since no cryoprotectant use is needed.