Comparative introduction study of Syringa vulgaris L. cultivars in the conditions of a moderately continental, continental and conditionally subtropical climate of the Mediterranean type

The article presents the results of a comparative i ntroduction study and cultivar evaluation of 7 of common lilac cultivars in the collections of three botanical gardens (the Nikita Botanical Gardens, the Central Siberian Botanical Garden and the Donetsk Bota nical Garden) located in zones with conditionally subtropical, te mperate continental and continental climate. It is established that the cul tivars retain their decorative features in the conditions of introducti on and show ecological plasticity, increasing their growing season with an increase in the vegetation period, as well as reducing the area of the leaf blade with a decrease in the average annual precipitation. Syringa vulgaris L. and cultivars created on the basis of this spec ies are among the most popular beautiful-flowering shrubs. Introduction of lilac is carried out in many botanical institutions, including the Nikita Botanical Garden s (Russia, Yalta), the Central Siberian Botanical Garden (Russia, Novosibirsk) and the Done tsk Botanical Garden (DNR, Donetsk). These botanical gardens are located in di fferent climatic zones, and therefore a comparative study of the growth and development rhy thms of lilac cultivars, as well as their comparative cultivar assessment, is of great intere s . Nikita Botanical Gardens (NBG) is located on the So uthern Coast of the Crimea (SCC) in a zone with a conditionally subtropical Mediterr anean climate [1]. The main climatic features here are very mild winters and dry moderat ely hot summers, the predominance of precipitation in the cold period of the year (from November to March). The average annual precipitation is 589 mm. The species Syringa vulgaris L. was introduced to the NBG in 1813, and then its forms and cultivars were introdu ced, as well as other species of the genus Syringa. At this time, 80 species, cultivars and fo rms are being introduced. Donetsk Botanical Garden (DBG) is located in the st ppe zone, characterized by a moderately continental climate with sharp fluctuati ons in air temperature, low humidity, * Corresponding author: zykova@mail.com © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). BIO Web of Conferences 38, 00144 (2021) Northern Asia Plant Diversity 2021 https://doi.org/10.1051/bioconf/20213800144

uneven seasonal distribution and significant year-by-year fluctuations in precipitation (from 223 to 655 mm), frequent soil and atmospheric droughts. The region is also characterized by a high level of environmental pollution due to a significant concentration of environmentally hazardous industrial enterprises. Under the influence of unfavorable environmental and climatic conditions, the xeromorphic structure of leaves prevails in woody plants [2].
The formation of the collection of the genus Syringa in the DBG was started in 1970, when about 100 S. vulgaris bushes were planted in the arboretum in the collection of the Oleaceae family, and other species of the genus were planted in the following years. In 1978, the Syringa collection and exposition site ("Syringariy") was established, on the territory of which 12 species, 4 subspecies and 6 forms of the genus Syringa, as well as 140 cultivars, mainly S. vulgaris, currently grow.
Central Siberian Botanical Garden (CSBG, Siberian Branch of the RAS) is located in the forest-steppe zone of the south of Western Siberia and is characterized by a continental climate. The duration of the winter period here is about 155-160 days from the first days of November to the end of March, the average temperature is -19°C. The spring period is characterized by a rapid increase in positive temperatures, but in the second half of May there is a return of cold weather, late spring frosts. The average annual precipitation is 460 mm [3].
In 1986, Laboratory of dendrology at the CSBG started of introduction work with S. vulgaris cultivars in order to create a collection of the most promising cultivars for the continental climate of the forest-steppe zone of Western Siberia. During the period of work, 126 cultivars of foreign and domestic selection were tested. Currently, there are 26 cultivars of common lilac cultivars in the collection, recommended for landscaping of Siberian cities [4] The objects of research in this work were 7 cultivars of S. vulgaris common to the three The results of a comparative study of the time and duration of the growing season and the flowering period of cultivars are presented in Table 1.
The beginning of the growing season of lilac cultivars in the NBG falls on the third decade of February -the first decade of March, and the end -at the end of October -the second half of November. The average duration of the growing season ranges from 241 days for 'Sensation' cultivar to 259 days for 'Katherine Havemeyer' cultivar. 'Katherine Havemeyer' and 'Nadezhda' cultivars bloom early, have a maximum flowering duration  Table 2. It should be noted that significant differences were found for all cultivars and not for all analysed parameters. There were no significant differences in the main indicators describing the decorative value of the analysed cultivars, such as the duration of flowering, the structure and size of flowers and inflorescences, however, the greatest variability in the length of inflorescences and their slightly larger average sizes were noted under the conditions of the SCC. The decrease in the area of the leaf blade noted in most cultivars under the DBG conditions is apparently associated with a decrease in the amount of precipitation and is a xeromorphic trait, which also indicates the ecological plasticity of common lilac cultivars. The studied cultivars are well known and popular. Our studies have shown that they retain their decorative effect when introduced in various climatic zones.