The adaptive potential of the Rosa canina L. rootstock obtained in vitro in the conditions of the south of Western Siberia

Garden roses are reproduced by grafting cultivars on resistant rootstocks, predominantly intraspecific forms of Rosa canina L. The underground part of these rootstocks is winter-hardy even in the forest-steppe and southern taiga of Western Siberia. However, their shoot systems of formation (SSF), on which generative shoots are formed, related to the type of shortened fruit, are damaged during the wintering period. After extreme wintering, R. canina plants of ontogenetic states g1-g3 for one year can pass into the state of “temporarily non-flowering”. In the Central Siberian Botanical Garden of the SB RAS (CSBG, Novosibirsk), long-term studies of seasonal development, ontogenesis, biomorphology, reproductive biology and winter hardiness of wild rose species from the Caninae Crėp sections are carried out. For the first time, the results of a long-term study of winter hardiness and seed productivity of the selected form of R. canina were presented, and an assessment of the SSF after extreme wintering, characterized by various damaging factors, were carried out. The aims of the present study were to establish in vitro conditions and propagate through direct organogenesis a promising winter-hardy form of R. canina used as a rootstock for garden roses, as well as to assess the adaptive potential of plants obtained by micropropagation under continental climate. In vitro experiments were carried out on a winter-hardy form selected in the CSBG from F3 plants of local reproduction. The primary explants were meristems with two leaf primordia isolated from axillary buds of annual vegetative shoots. At the establishment stage the explants were cultured on hormone-free modified liquid Murashige and Skoog’s medium (MS) supplemented with 100.0 mg/l glutathione and 30.0 g/l glucose. Direct organogenesis was induced on MS medium supplemented with 2.0 mg/l 6-benzylaminopurine (BAP) and 1.0 mg/l 3-indoleacetic acid (IAA). MS medium with 1.0 mg/l BAP was used for shoot multiplication. A hormone-free half-strength MS medium supplemented with 1.0 mg/l IAA was used to root the obtained microshoots. The regenerants were grown in containers with sterile sand, then in pots with a substrate consisting of a mixture of peat with perlite, humus, sand, and coconut substrate (1:1:0.5:0.5) and transferred to soil culture. Further studies were carried out in 2015-2021 on the experimental plot of the CSBG, located in the forest-steppe zone of the south of Western Siberia (Novosibirsk, Akademgorodok), which is characterized by a continental climate. In the study of morphogenesis, classical and modern biomorphological approaches were used, which consider the shrub form as a complex shoot systems of formation in space and the change of these systems in time. The seasonal dynamics of starch in the shoots was studied using a reaction with iodine in potassium iodide. Seed productivity was determined. At the multiplication stage, 8±1 microshoots per explant on MS media with 1.0 mg/l BAP was obtained. The in vitro rooting frequency was 60.0 % with a mean number of 2.0±1.0 roots per microshoot on half-strength MS with 1.0 mg/l IAA. It was revealed that the pregenerative period in vitro-derived R. canina plants is reduced by a year, compared with ones of seed origin. Plants enter the ontogenetic state g1 in the third year, and the formation of partial bushes, which can be used to seed plantations, begins in the fourth year of vegetation. Under the conditions of the continental climate of the forest-steppe of Western Siberia, all in vitro-derived specimens of the selected form had annual fruiting on shoots above the snow cover. The exception was 2020-2021, however, even after a severe wintering, hypanthia formed in the lower part of the SSF. A prolonged decrease in temperature to -30 °С in December led to partial damage to the middle part of the SSF, while a short-term decrease in air temperature to -28 °С in January did not cause serious damage even to the middle part of the SSF. The selected form was also resistant to strong spring frosts in the second decade of May. With favorable wintering and the preservation of terminal buds, the SSF of mature generative plants (g2) continued to increase in height. The combination of two favorable wintering periods in a series led to the formation and preservation of powerful SSF up to 2 m tall, as well as to the formation of mainly 2-3 hypanthia with a high number of completed seeds on short fruit shoots. Starch hydrolysis in those shoots of R. canina , in which complete leaf fall was observed in October (phenophase L5), was almost completed in November. However, single starch grains were still in single-row and multi-row medullary rays, as well as in the perimedullary zone.