Features of long-term preservation of Azhurnaya and Bergamotnaya mint cultivars in an in vitro collection

Mint represents a valuable medicinal and essential oil plant widely used in pharmacology, perfumery, cosmetics, and food industry. In order to maintain collections of cultivars and valuable samples, as well as to carry out breeding, the application of biotechnology appears to be promising for in vitro preservation of plant objects under the conditions of slow growth at low positive temperatures. The present study is focused on the morphometric parameters and genetic stability of the explants of two mint cultivars during their in vitro preservation at 4–6 ºС for a year without illumination. Meristems with two leaf primordia were cultivated on a nutrient medium in a culture room at 26 ºС and illumination of 2–3 klx with a 16-hour photoperiod. Microshoots developing from meristems were divided into single-node stem segments to be used as explants for deposition. After a year of deposition at 4–6 ºС without illumination, the number of viable explants in the Azhurnaya and Bergamotnaya cultivars was established to be 56.5 and 85.7%, respectively. The explants under study were characterized by the development of up to 2.5 shoots up to 13.2 mm long and rhizogenesis with a frequency of up to 52.3%. Following the deposition, microshoots were cut and transferred to a culture room to resume growth. After two subcultivations, viability (100%), morphometric parameters of microshoots, and multiplication index (up to 5.5–7.3) were fully restored. The ISSR-analysis performed according to four studied DNA markers revealed the microshoots of these cultivars to be completely identical to the original plants after in vitro preservation. The conducted studies proved the effectiveness of the conditions used for in vitro preservation of mint explants and confirmed the explant genetic stability after a year of deposition at 4–6 ºС.