Survival of Sweet Potato Meristems Under Different Cryopreservation Regimens

Abstract

The introduction of vegetable crops with a high content of biologically active compounds into agriculture has still remained an actual task. The sweet potato (Ipomoea batatas) is one of the vegetables successfully cultivated in Europe. Its root tubers are rich in sugars, which determine its taste, as well as the proteins, B vitamins, ascorbic acid, carotenoids, macro- and microelements [A.E.Z. Triqui, 2008]. The in vitro culture and cryopreservation are the efficient methods for preserving plant diversity and establishing plant genetic collections. However, in order to determine the possibility for a long-term preservation of sweet potato meristem tissues it is necessary to design the cryopreservation technique, which could provide a high viability level for plant material. This research was aimed to compare different regimens for cryopreservation of sweet potato meristems. The apical and lateral meristems, isolated from in vitro cultured plant-regenerants of Bonita variety sweet potato were the research objects. The meristems of up to 1 mm size with 1–2 primordias were separated with a discission needle under sterile conditions, then placed by 5 pieces into glass vials with agarized nutrient medium, supplemented with 0.1 mg/l benzylaminopurine, 0.5 mg/l naphthylacetic acid and 2.0 mg/l gibberellic acid. Prior to cryopreservation the explants were treated with cryoprotectant solutions for 60 min at 22°C, and then placed in 1.8 ml cryovials. The meristems, saturated with 1.5 M dimethyl sulfoxide were cryopreserved with 1 deg/min cooling rate down to –30°C, followed by immersion into liquid nitrogen; the ones treated with the solutions for vitrification (1 M sucrose + 2 M glycerol + 2.5 M ethylene glycol (PVSN) and (44% glycerol + 44% sucrose (PVS3)) were directly immersed into liquid nitrogen. The objects were thawed by immersing cryovials into a 40°C water bath. The survival was determined by a number of meristems, which remained green within 14 days. The observation of thawed meristem showed that the highest number of survived specimens was obtained after PVSN application, i. e. 75%. The use of 1.5 M dimethyl sulfoxide allowed obtaining about 65% of the survived meristems. The lowest survival (40%) was found in the PVS3-processed samples, which might be explained by a toxic effect of this solution on meristems. Thus, in order to establish the collections of sweet potato varieties at a low temperature bank, it is expedient to apply the vitrification with PVSN due to a high survival rate of frozen-thawed samples and its simplicity.