Seasonal rhythm of development of Allium trautvetterianum in the Kulyab Botanical Garden

The article deals with the seasonal rhythm of development of the bulbaceous acrosympodially accreting polycarpic Allium trautvetterianum Regel (the subgenus Melanocrommyum) when growing in the Kulyab Botanical Garden of the Khatlon Scientific Center, Academy of Sciences of Tajikistan in 2010-2015. Duration of vegetation and phenological phases is described. The species is characterized on the phenorhytmotype as a shortgrowing ephemeroid. Influence of weather conditions on duration of phenological pahses is shown. It is established that the rhythm of development completely corresponds to the eastern variant of Mediterranean climate.


Introduction
Seasonal rhythm of development of plants is a representation of their life cycle which is shown in repetitive phenophases.Study of phenophases is necessary for understanding for plant community functioning [1].The change in time and duration of the passage of phenophases to adjust to new conditions is one of the indicators of plant adaptation to changing environmental conditions.In the context of climate change, the importance of phenological study is currently increasing.
According to current data the genus Allium L. numbers about 900 species.Onions are widespread in the northern hemisphere and represent one of the largestgenera of the world flora [1].The subgenus Melanocrommyum contains 170 species, the range of which is mainly restricted to the region of Ancient Meditarrenean [2].Thirty one species of this subgenus grow in Tajikistan.
It is known that Melanocrommyum species on the rythm of development belong to ephemeroids.A short period of vegetation and duration of stay in dormancy as a bulb most of the year are typical of them [3,4].Information on seasonal development of some onions of the subgenus Melanocrommyum is mainly availablein the works on introduction of them in different regions of Russia [4][5][6]; Uzbekistan [3]; the Ukraine [7]; and Germany [8].

Material and methods
Allium trautvetterianum is an endemic plant of the south-western Pamir-Alay, it grows in the semisavanna belt with domination of Prangos pobularia, Organum tyttanthum, Salvia sclarea, Hypericum scabrum, Taeniatherum asperum, Poa bulbosa, and Carex pachystylis, in the shibliak belt with domination of Pistacia vera, Crataegus pontica, and Amygdalus bucharica, and occurs at the exposure of vaiegated at an altitude of 700-1700 m above sea level.
The species has been cultivated in the Kulyab Botanical Garden since 1999 г.Onions were collected on the Dzhilantau Ridge (Temurmaliksky Region, Southern Tajikistan) [9].Development of A. Trautvetterianum was observed durring 5 years from 2010 to 2015.Seasonal development was studied by the method of I.N.Beideman [10].Duration of a concrete given phase was determined by development of 10-20 individuals per introduction population.Belonging to the phenorhythmotype was determined according to the I.V. Borisova classification [11].
The following phases of phenological development: vegetation, duration of functioning of the assimilation apparatus, growth of the flower stalk, budding, blooming, fruiting and dissemination were identified because of development pattern of onions as rosette plants .
Annual meteorological data of the research location were taken from the summaries of Kulyab weather station.

Results and discussion
I.G.Serebryakov [12] considered a seasonal rhythm of plant development to be one of the features reflecting adaptation to ecological-phytocoenotic and climatic conditions of growth.
The climate of Tajikistan generally belongs to the eastern variant of the Mediterrenean climate [13].Kulyab and Kulyab Botanical Garden are located in southern Tajikistan at an altitude of 640 m above sea level in the valley of the Yakhsu River.Kulyab is characterized by insufficiantly humid climate, dry summer, moderately mild winter.The mid-annual air temperature is 16,4°С, sometimes in summer it rises up to 44-46°С, in winter, in certain years, it falls to 17-21°С.Duration of the frost-free period is 260-309 days, and the sum amounts to 5800-6000°.The period with temperature of more than 10°С lasts 240-250 days.The effective heat sum for this period is 2800-3000°.In the hot season often blow dry southern winds in the form of dust storms.Large temperature changes are observed not only during a year, but also during a day.There is a lot of precipitation-529 mm, but its distribution is very uneven.Up to 70 % of the annuak norm of precipitation falls in winter and spring [14].Very little rain falls in summer.The period from June to September, at high air temperature, it is almost or rainless at all.The soil is dried out.Stable snow cover, only some centimeters, is formed very seldom.
Allium trautvetterianum is a perennial herbaceous, acrosympodially accreting, nonparticulating bulbous polycarpic plant.Annually unfolds one rosetted shoot consisting of a shortened part with 3 scale-shaped and 2-3 assimilative leaves and leafless flower stalk.The length of a flower stalk reaches 50 cm.Leaves are lanceolate, upward, 2-3cm wide, with an axil up to 3-6 cm.A basal part of the shoot forms a tunicate ovate bulb 1,5-2,5cm in diameter.The bulb is formed by membranous cover scale, storing scale, vaginate scale and axils of green leaves.Outside it is covered with greyish, almost papery splitting sheaths -leaf remnants of previous shoots.Additional roots are thin numerous, superficially arranged, develop on the bulb stem and are annually substituted by new ones.An inflorescence is dense many-flowered globe-shaped or umbellate thyrse.Like most species of the subgenus Melanocrommyum, it belongs to ephemeroids by the seasonal rhythm of development.A regeneration bud is laid in the bulb 3 years before development.Generative organs are completely formed by autumn previous to the growing season.For 6 years of observations vegetation of A. trautvetterianum lasted from 71 to 81 days in the Kulyab Botanical Garden.However, vegetation periods differed substantially in various years.The earliest plant growing and emergence of the first leaves were noted in the first decade of February in 2010 and 2015, and the latest one -in the first decade of March in 2013-2014 (Fig.1).