METHODS FOR OVERCOMING SEED DORMANCY AND FEATURES OF IRIS CULTIVATION IN <i>IN VITRO</i> CONDITIONS
Background . The state of organic seed dormancy is an important adaptation mechanism for the conservation of the species. However, the presence of deep dormancy makes the cultivation of many plants difficult. The development of methods and technologies for growing plants in vitro allows to preserve some rare species. This method allows to obtain healthy planting material and significantly speeds up the process of breeding new varieties as well as preserves the genetic resources of cultivated and wild plant species. The purpose of this research is to study the peculiarities of overcoming the dormancy of iris seeds and the subsequent introduction of seedlings into in vitro culture. Materials and methods . The seeds of the studied iris varieties ( Iris pseudacorus L.; I. graminea L.; I. ensata Thunb.; I. missouriensis Nutt.; I. sibirica L.; I. halophila Pall.) were collected in 2017-2018 in Penza Botanical Garden named after I. Sprygin. In laboratory conditions were studied the features of seed germination under the influence of various factors - the change of temperature and light, scarification. Sprouted seeds were planted in vitro . The explants were cultured in sterile conditions on a nutrient medium Murashige , Skoog with the addition of phytohormones - auxin (0,5-2 mg/l) and Gibberellin GA<sub>3</sub> (2 mg/l), sucrose content - 20 g/l, glucose - 20 g/l. 10 seedlings of five plant species were grown under natural light and at room temperature. Results . During the study it was found that laboratory germination of seeds after cold dry stratification reached its maximum at +3 °C. Illumination had no effect on seed germination in the studied plant species. At the same time pre-freezing increased seed germination. It was also concluded that the less the seeds were in storage, the higher their germination was. Among the studied species of irises, the Siberian iris ( I. sibirica L.) turned out to be the least whimsical and this sort has the highest percentage of seed germination. Optimal conditions were selected for the introduction of iris seedlings in vitro . A scheme has been developed for the introduction of plants of Iris into the medium in vitro , thanks to which it is possible to obtain plants with 93 % seed germination and with an 80 % guarantee that no pathogenic organisms will grow in the nutrient medium. The important points in the cultivation of irises in an artificial environment are the correct sterilization of seeds, the removal of the seed coat and the selection of a suitable nutrient medium. Conclusions . The influence of temperature, illumination and cold dry stratification on the germination of iris seeds disturb the deep dormancy of I. pseudacorus L., I. graminea L., I. ensata Thunb., I. missouriensis Nutt., I. sibirica L. seeds and promote their germination. To disturb the dormancy of I. halophila Pall seeds it was essential to use additional scarification. Also there was created a special way of seed sanification before planting them in vitro : 0,5 % KMnO<sub>4</sub> (15 minutes) → 1 % CuSO<sub>4</sub> (15 minutes) → 70 % ethanol (1 minute) → 3 % solution of H<sub>2</sub>O<sub>2</sub> (1 minute) → repeated washing with sterile distilled water. The composition of the nutrient medium for in vitro cultivation was also selected as follows - the Murashige, Skoog medium with the addition of 3-indoleacetic acid (2 mg/l) and GA<sub>3</sub> (2 mg/l), the content of sucrose is 20 g/l, glucose is 10 g/l.