Candidate Biol. Sci. A.V. Kelina

The State Research Institution All–Russian Scientific and Research Institute of Floriculture and Subtropical Crops of the Russian Academy of Agricultural Sciences, c. Sochi, Russia, e-mail: cvetovodstvo@vniisubtrop.ru

Deciduous shrubby magnolias in Russian humid subtropics

Листопадные кустовидные магнолии – красивоцветущие декоративные растения, культивируемые во влажной субтропической зоне России. Приводятся данные о распространённости в регионе представителей рода Magnolia L. Обсуждается вопрос таксономической принадлежности M. × lennei Houtte. Даётся описание методики обрезки растений и получения черенков, для выращивания посадочного материала.

Ключевые слова: кустовидные листопадные магнолии, влажные субтропики России, вегетативное размножение

Magnolia L. genus includes about 80 species, spread in East Asia and North America. The representatives of the given genus are shrubs, as well as evergreen, deciduous and shrubby trees [1, 2]. Plants blooming in spring are mostly represented; deciduous shrubby magnolias are perhaps the most ornamental and exotic among them. It is due to their large flowers with an attractive color and ability to bloom before the leaves appear [3]. Magnolia liliaeflora Desr. is mostly common among deciduous shrubby magnolias in the zone of Russian humid subtropics. There are also the following hybrids with its participation: M. × soulangeana Soul.-Bod. and M. × lennei Van Houtte - nearly a quarter of the existing taxa [4,5]. Exactly this species was selected as the main research objects. This group of magnolias is represented mainly by garden forms of seed origin; therefore, the study of their form diversity is highly relevant [6]. However, cultivation of these spectacular plants is insufficiently developed and associated with some bio-ecological difficulties.

The given research has got the following tasks: analysis of species and cultivars diversity of deciduous shrubby magnolias in Russian humid subtropics, as well as study of the peculiarities in vegetative propagation of deciduous shrubby magnolias under the regional conditions, as a method to increase their representation.

The main researches were preceded by the detection and identification of species and forms of shrubby magnolias in the region. The identified species and forms of deciduous shrubby magnolias were visually examined. Besides photographic images and samples, collected for their further identification, a detailed description of special features in species and forms was conducted by completing working cards with the following information: name, location, description of shoots, leaves, buds, flowers and their parts, as well as the presence of smell, fruits and seeds, affection of diseases and pests, degree of winter hardiness and planting pattern.

During the study, we have ascertained the following data: diversity of magnolia species and forms includes 79 taxa in gardens and parks of Russian humid subtropics. Deciduous shrubby magnolias are represented by 6 species and 19 garden forms in the region, i.e.: M. × lennei Houtte (cv. Atropurpurea, cv. Aurora, cv. Nona, cv. Roseolineata), M. liliaeflora Desr. (cv. Gracilis, cv. Nigra, cv. Purpurea, cv. Reflorens), M. sieboldii K. Koch, M. sinensis Stapf, M. × soulangeana Soul.-Bod. (cv. Alexandrina, cv. Alexandrina Alba, cv. Andre Leroy, cv. Brozzoni, cv.Norbertii, cv. Rustica Rubra, cv. San Jose, cv. Verbanica), M. stellata Maxim. (cv. Rosea, cv. Royal Star), Magnolia cv. Susan. It should also be noted that there is a large number of new growths obtained from open pollination.

The typical forms of M. × lennei and M. × soulangeana are allocated very conditionally in the practice. They include some plants of seed origin that have not got any obvious signs of the famous garden forms.

A problem of taxonomic properties in hybridogeneous M. × lennei deserves special discussion. Its representatives are shrubs with long-lived shrubs with stipes. Thus, the representatives of M. × soulangeana are typical shrubby trees with a shortened stem and a shifted down zone of active branching. Outwardly, two this species are similar, but the peculiarities of their culture, as the practice shows, are different. M. × lennei is more shade-enduring, and tolerates close planting, renewal pruning and transplantation in adulthood. M. × soulangeana is light-requiring, and tolerates no close planting or renewal pruning or transplantation in adulthood. These differences are essential for use in landscape gardening and agricultural techniques [7].

The researches made in this field by both our and other authors, have shown that there are some differences in venation of leaves and their pubescence (in M. × lennei they are pubescent only below), as well as in blooming ( M. × soulangeana has got a basipetal blooming, and the florets are oriented along the axis of the shoot, while M. × lennei has got a acropetal blooming, and the florets are upward), in the surface of the pericarp and its anatomy, in the structure of epicuticular wax paleolas, as well as some significant differences in the shape and structure of stomata. The whole thing convincingly indicates the independence of this two hybridogeneous species.

World assortment of M. × soulangeana, including garden forms of M. × lennei, and M. liliaeflora, numbers about two hundred cultivars. The conducted introduction search has revealed a significant introduction potential, i.e. more than one hundred promising cultivars can be recommended for cultivation in the humid subtropical zone of Russia. The practice has shown that container seedlings from foreign nurseries are well adapted in the given region, despite the specific soil and climatic conditions in the humid subtropics.

Only standard forms, which are not always sufficiently ornamental and uniform, can be efficiently propagated by seeds. Seed plants bloom much later than those propagated vegetatively. All the considered magnolias can propagate vegetatively under certain conditions, i.e. by cuttings, offsets and engrafting. Propagation by cuttings is the most productive, since a high reproduction rate was recorded. But this is prevented by some climatic characteristics in the given region. We also have found that the optimal condition of shoots for obtaining cuttings is the stage of partial lignification of the growing shoots, which is observed at initial stage of flower buds formation; the terms are late June - early July. There is a hot weather with daytime air temperatures above 30˚ C in the region is at this time, the optimum temperature for cuttings rooting should not exceed + 23˚ C. Exactly this condition prevents effective reproduction [8].

We have developed a method of shortening vegetative shoots with the aim to have a later formation of flower buds in order to obtain cuttings from deciduous shrubby magnolias of the required physiological state in specified time frames. Initially, these agro-technical measures were predominantly considered as means to increase the number of flower buds in the plants, as well as to prolong flowering time, due to the alternative formation of flower buds in the shoots of the second generation. In addition, the method of shortening summer shoots at the final stages of their development allowed to obtain more compact plants.

Successful resumption of shoots growth after such pruning allowed to repeat a similar procedure at the next stage of flower buds formation in shoots belonging to the second generation. As the shoots of the second generation successfully came to this development stage, the vegetation season being not over, a third shortening pruning was made, which contributed to the beginning of the third shoots generation.

Initial formation of flower buds in the shoots of the third generation takes place in the third ten-day period of September, when daytime maximum temperatures exceed +23˚ C rarely and briefly. The warm period of Russian humid subtropics continues at least until the early December. During this time, within two months, the formation of roots in stem cuttings of deciduous shrubby magnolias occurs [9].

Thus, the system of summer pruning of shrubby deciduous magnolias allows to prolong the flowering period half again as much and to get cuttings of a necessary physiological maturity at the optimum terms.

The conducted studies allow to develop a science-based system of breeding and cultivation of shrubby deciduous magnolia in urban park type-ecosystems in subtropical Black Sea coast of Russia.

Deciduous shrubby magnolias can be used in all types of parklands (except for natural protected areas). They are recommended for use as solitaires and small monogroups consisting of all types of green spaces, and as an element of container plantations.

References

1. Treseder N.G. Magnolias. London: Faber & Faber, 1978. 243 p.

2. Liu Y. Magnoliaceae / Y.Liu, N.Xia, L.Yuhu, H.P.Nooteboom // Flora of China, 2008, V. 7. – P. 48-91.

3. Dorothy J.Callaway. Magnolias. B.T. Batsford LTD, London, 1999.260 p.

4. Гинкул, С.Г. Магнолиевые в советских субтропиках [Текст] / С.Г. Гинкул. - Батуми: Издание Госиздата Аджарии, 1939. – 46 с.

5. Карпун, Ю.Н. Субтропическая декоративная дендрология [Текст] / Ю.Н. Карпун. – СПб: изд-во «ВВМ», 2010б. – 580 с.

6. Колесников, А.И. Декоративная дендрология [Текст] / А.И. Колесников. - М.: Лесная промышленность, 1974. – 632с.

7. Келина, А.В. Особенности организации Сада магнолий на Черноморском побережье Кавказа / А.В. Келина, Ю.Н. Карпун // Проблемы современной дендрологии: матер. междунар. науч. конф., посв. 100-летию со дня рожд. член-корр. АН СССР П.И. Лапина. – Москва, 2009. – С. 158–160.

8. Келина, А.В. Вегетативное размножение листопадных магнолий в условиях Черноморского побережья Кавказа / А.В. Келина, Ю.Н. Карпун // «Вестник ИрГСХА». – Иркутск, 2011. – Вып. 44. Ч. IV. – С. 53–58.

9. Келина, А.В. Магнолии листопадные из черенков / А.В. Келина // Цветоводство. – 2009. – № 3. – С. 26–27.