Structure of vegetative organs in essential oil rose under standard culture conditions and long-term conservation in vitro

Creating an in vitro gene bank of essential oil rose (Rosa × damascena Mill.) makes it possible to preserve and efficiently propagate valuable cultivars. We optimized clonal micropropagation and conservation in vitro for the cultivars: ‘Festivalnaya’, ‘Raduga’, ‘Lany’, ‘Michurinka’, ‘Iskra’, and ‘Kooperatorka’. Meristems were introduced in vitro, regenerants were cultured on Murashige and Skoog MS medium with 0.1 mg L^‑1 NAA, 0.5 mg L^‑1 GA₃, 0.5-1.5 mg L^‑1 BAP in the growth chamber at 25±1°C under 16-h photoperiod with a light intensity of 37.5 μmol m^‑2 s^‑1. Conservation was carried out on ½ MS medium contained 0.2-0.4 g L^‑1 chlorocholine chloride CCC and 60 g L^‑1 sucrose at 4±1°C, 16-h photoperiod with a light intensity between 1.25 and 3.75 μmol m^‑2 s^‑1. To determine some structural features of vegetative organs, microshoots were compared between those collected after 9 months of the culture in vitro, to those after 36 months of storage in the gene bank. When cultured in vitro, essential oil rose plants produced 2-3 microshoots per explant. Their height was 2.4-5.6 cm and each micro shoot carried 6-9 ternate leaves. Leaf-blades were 79-121 µm thick, hypostomatous, bifacial, with differentiated mesophyll (palisade index 0.37-0.50). Covering tissues are composed of a thin cuticle and a single layer of the epidermis. The stomatal apparatus was of anomocytic type with 71-102 stomata mm^‑2. The average shoot height under conservation was 1.5-3.2 cm and no more than two microshoots per explant formed. The part of simple, large (0.9×1.1 cm) leaves was 30-50% and ternate leaves were also noticed. Leaf-blade thickness was 80-110 µm, palisade index – 0.37-0.41. There were up to 265 stomata mm^‑2 of the abaxial leaf surface. Thus, on microshoots of six essential oil rose cultivars morphologically and anatomically normal leaves were structured with the ability to active assimilation that indicates their high morphogenic capacity during micropropagation and conservation in vitro.