Stevia - a perennial plant that belongs to the department of higher plants - Kormobionta, type angiosperms - Angiospermae, class of flowering - Dicotyledoneae, Compositae order - Compositales, family Asteraceae - Asteraceae, genus - Stevia, type - rebaudiana - Stevia rebaudiana Bertoni.
The family to which the stevia, a lot of numerical, has more than 20,000 species. This is a relatively young plant, which is in the phylogenetic bloom, which continued process of speciation.
Stevia - perehresnozapylna plant mainly entomofil. However, in the literature there is some evidence of obligate apomixis in stevia, as well as self-pollination.
Stevia plants differ greatly in form and habit bushes, stems and shoots. Depending on the length and number of lateral shoots angle
attach them to the stem and oblystyanosti, isolated over ten forms of stevia plants. Some authors identify morphological types 25-30 stevia.
The shape shrub Stevia - morphological and economic sign. Most often found in our environment such forms of bush:
1. oval (egg-shaped) shape - the widest part of the bush below the middle, gradually tapering down and vytyahuyuchys to top.
2. The spherical shape of the bush - bush has rounded shape.
3. sprawling form - the widest part of the plant is in the middle of the bush.
4. The inverse-conical or pyramidal form - the widest part of the plant is in the upper part.
5. inverse-trapezoidal form - the widest part of the top of a bush, gradually tapering down.
6. cylindrical or elongated shape - the same width at the top and bottom of the bush.
7. pyramid-shaped bush - when bush gradually flaring.
There are also spindle-shaped and conical shape.
The height of shrubs, depending on climatic conditions and soil moisture year - ranging from 45.0 to 120 cm.
Stevia bushes are erect or fallen. Well feathered. The diameter of the stem at the base of 1, 0 to 1.5 cm. Plants first year of having one main stem of the side stems. At 2-3 year stems grow as much as was laid buds on the rhizome.
In countries where stevia grows as a perennial culture, the number of stems is 80 or more. In our conditions, stevia grows as an annual amount of culture and kidneys, which lie at the end of vegetation roots. Ranging from 1-2 to 18-19. Oblystyanist plant Stevia determined by the number of leaves on the bush, their shape, size. Angle of deviation from the stem, the size and length of internodes. This figure does not only affect the performance of stevia, but is stable morphological characters.
Area stevia leaves on the stem-opposite pairs, a pair of upper leaf node is placed at right angles to the axis of the lower leaf node. Leaves sessile. With a very short petioles. In the bosom of every leaf is a bud, which gives rise to axillary stems.
Stevia leaves are small, a lot of people. According to the laboratory. Their number one bush varies from 350 to 1200 pieces. Larger sheets placed on the main stem and the lower part. At the top of the stems leaves smaller. The size of Stevia leaves depends not only on the variety of plants, but also on the growing conditions. Thus, in the Crimea, the length of diploid plants stevia leaves an average of 7.8 cm., Width - 3.4 cm; tetraploid plants respectively - 8.2 and 4.3 cm.
In the forest-steppe zone of Ukraine diploid stevia leaf length averaged 5.4 cm., Width - 2.3 cm tetraploid respectively - 6.2 and 3.3 cm.
Stevia leaves are hairy on both sides, but less rapidly than stem. The edges of the leaf plate in the upper third - with rounded or sharp teeth, color - green or temnozelenyy. The form of the leaf blade oval at all, but very variable. Groups numbering up to 8-9 leaves of different shapes: wide or narrow, wedge-shaped, elongated, ellipse, romboyidni, ovate, inverse-ovate, lanceolate, rounded.
For a set of attributes associated with leaves, stevia studied biotypes. What were grown in the Crimea, were merged into three groups.
The first group includes small puff biotypes stevia's inverse-conical or pyramidal shape shrub. Stems not fallen, with short internodes, well about deciduous. Leaves sessile, smooth or slaboopusheni. Plants of this group have a short growing season. During the cleaning plant height is only 65 cm long kvitkuvannya continues. Seeds ripen simultaneously. Performance Plants of this group is low. This Early biotypes.
The second group included biotypes with leaves of medium size, well about broad, with a long growing season (middle-biotypes). During the cleaning plant height is 80 cm. The capacity of these plants is higher than the first group.
The third group includes biotypes with large leaves, inverse-trapezoidal shape shrub, plant height of 90 cm, pubescent leaves, stems not fallen with growing period to 120 days. Vintage biomass is high, but glycosides accumulate much less.
For economic characteristics are more important indicator of dry leaves and crop accumulation in these sweet glycosides.
Steviya- plant short daylight hours, it decreases it goes to the generative development. Therefore, in different geographical areas stevia will develop differently: the closer to the equator, the shorter of stevia will during the growth of the vegetative mass and, conversely, the distance from it to the north or south, plants may long to develop, flowering they delayed and they accumulate large vegetative mass.
When growing stevia should take into account its biological properties: the requirements for temperature, resistance to low temperatures, the requirements for soil and moisture, and others. These features Stevia due to its unique conditions of the home (in Paraguay). The climate in Paraguay is subtropical, but stevia is derived from the central part Amambey, with special conditions: extreme changes in temperature, fog, winds, rains and high occurrence of groundwater. This also caused a short root system of stevia, its resistance to waterlogging. Especially demanding to moisture stevia in the early and mid-growing season. After planting it in the field and during growth. Stevia does not tolerate drought, so when its cultivation in areas with insufficient moisture, you need to apply the glaze.
Stevia is not resistant to low temperatures and at temperatures below 12 0C hardly developed, sensitive to frost. In laboratory parameters examined temperature stability of different age and nature of genetic forms of stevia. Given the sensitivity of this culture to the morning frost, studied its cold resistance at 0 0 C; -1-2 And -4-5 0C 0C in artificial climate chambers. It was found that the plant Stevia in vitro withstand short-term (up to 5 hours) to reduce the temperature -1-2 0C. Not poshkodzhuvalys plants and 5.7 hours after lowering the temperature to -5 0C. But for longer (12 hours) holding plants at this temperature plants completely die. The temperature of -5 0 C at 12-hour exposure and more critical to the culture. Therefore, in the temperate climate of Ukraine can be grown in vivo as annual crops because the winter freeze its roots.
By building underground organs Stevia belongs to kytytsekorenevyh herbs. In adulthood she does not have a root. Mochkuvata its root system consists of two types of roots: thickening, shortened length of 25 cm, which radially from the base of the stem, and a lot of thin, elongated roots, which are moving away from thickening. According to the laboratory technology of stevia, the number of thickened roots of one plant to the end of the first year of vegetation in the area forest-steppe Ukraine ranges from 32 to 155 units. Depending on the method of reproduction formed different number thickened roots: plants derived from green cuttings, form an average of 32 to 55 pieces, and plants obtained by in vitro, much more - from 64 to 155 pieces.
At the beginning of the growing season the primary root of the seed and extra thick and thin roots perform its basic function - the absorption of water and minerals from the soil. Laboratory experiments have shown, features fine roots compared to the much larger bulge.
At the end of the growing season increases the number of stevia thick roots that turn into spare organs for the development of the kidneys, which are laid on top of the thick roots near the base of the stem.
In those climates where stevia is grown as a perennial plant, roots remain in the soil, perezymovuyut, and with spring buds begin to develop stem. If climatic conditions do not allow the rhizomes in winter field stevia grown as annual crops. This rhizomes are dug in autumn and kept in special areas (vaults) to Spring to obtain one green cuttings for growing seedlings.
The root system is shallow stevia placed on the soil surface, which necessitates its irrigation during the growing season in areas with insufficient rainfall
Stevia Dynamics flowering, pollination and fertilization processes. Structure androecium and Hynek stevia.
In the open field in terms of Ukraine stevia starts kvituvaty mostly in September and October, and only some plants - in July and August. Flowering lasts one bush 1.5-2 months. Mass flowering occurs at a time when the air temperature, especially at night drops to 7-9 0C. Under such conditions the development of embryos is very slow and insufficient seed matures.
The flowers are very small in stevia bisexual, aktynomorfni, p'yatychleni. Corolla white with a purple tinge at the base, zrosnopelyustkovyy, tubular, has the shape of an elongated bell. The flowers are collected in baskets (five flowers in each), which in turn form a complex inflorescence - shield. Crete so. The flowers are characterized by well-defined proterandriyeyu when maturing pollen and anther cracking is closed buds. Buds, like the basket and in the inflorescence, are at different stages of development, which makes remontant flowering.
Calyx has the form of 16-18 pappus bristles. The five stamens attached to the corolla tube. Threads stamens - free, Piljaki - elongated, longitudinally cracked.
Hynek has pistil column that ends fishtail stigmas. Pistil stigmas viable within 10-12 days and significantly modified during flowering. Blades stigmas covered with papillae.
Ovary bottom, single nest, with one seed embryo placed on the short nasinnyenostsi - funikulyusi. Seed germ Tenu when the parent cell megaspor covered only the epidermis and lies directly beneath the epidermis mehasporiyu.
Getting embryo sac provides one of the four tetrads megaspor by three successive mitotic divisions. Seed germ anthropic, odnopokryvnyy. Monosporychnyy embryo sac, Polygonum-type, pretty narrow and elongated in shape.
As a result, the first cell division megaspory form two nuclei that differ to mikropilyarnoho halal and common-poles. Subsequently, each core simultaneously divided into two more times, so that at each pole is formed by four cores - the so-called eight nuclear stadiyatinochnoho hemetofita. The nucleus of the central cell embryo sac is formed by fusion of polar nuclei and thus formed the seven nuclear mature embryo sac of the egg apparatus and central cell.
Egg apparatus Stevia rebaudiana B. consists of two eggs and synerhid. Quite a large egg is pear-shaped, large nucleus and nucleolus, located in the apical part of the cell. Central embryo sac cell also has a fairly large nucleus with nucleolus. Antipodes located in common-halal of the embryo sac.
Pollen lotion on the pistil fall, mainly through insects. During flowering pistils stigmas extends significantly rising above corolla of the flower. Piljaki is placed below the shoulder blades stigmas. Coming out, they poured in the middle of the flower pollen that prevents anemophily. Stevia In most entomophile type of pollination due to which fertilization and embryo development.
After fertilization, the egg begins development of the embryo, which is the type of aster. Thus both cells (basal and apical) involved in the formation of the embryo.
Embryological analysis results indicate that within 4-5 days after flowering stevia nuclei have a spherical shape, and some of them begin laying humps cotyledons. On the 8th day become germ heart-shaped, remaining still quite small in size - 0,3-0,5mm. On the night of 12-16 cotyledons vydovzhuyutsya (length of embryos at this time varies from do1,5 1.0 mm) formed embryonic root and cap. At 20-30 day embryos morphological development of stevia ends. Length differentiated embryos of 2.0-2.5 mm, they are elongated. Full physiological maturation of embryos occurs only 35-40 days, and sometimes later.
At this time the embryo tissue harden nasinneva box darkens, seeds easily emptied from the Recycle Bin.
Stevia Fruit - achene with a thin oplodnem that is easily separated from the seeds odnonasinnyy. Seeds are small, elongated, fusiform, length of 2 to 3 mm, weight of 1000 pieces. is 0.4 hours, when ripe seed capsule becomes dark brown. The outer surface of the seed can be seen five or six light brown vertical stripes. Seeds must adapt to the villi in the form of proliferation of wind. Villi light brown bunch collected over the top seed. Under steppes stevia seeds mature enough, but in good years seed with a high germination can be obtained even in the open field. In recent years, the methods of obtaining seeds in the greenhouse and in processing plants stimulators.
Vegetative propagation of stevia.
Role of biotechnological methods in breeding stevia
a) microclonal reproduction of stevia in culture in vitro.
The method of in vitro propagation is very common in plant breeding and genetic research to improve the work associated with the development and introduction of new forms of plants. Microclonal allows a reproduction of the original plants from one to one million identical plants for six months and in the right quantity to propagate valuable breeding material.
For regeneration and propagation of plants stevia used various organs and tissues, mayor system, buds, stems, leaves and buds. According to II Ilienko for mass reproduction proved most suitable apical and lateral mayor system. Regeneration morphogenesis and stem and leaf explants is only possible through the formation of hormones kalusu on enriched environments.
To sterilize explants (growth points or axillary bud) used 0.04% mercuric chloride solution with an exposure of 30 minutes and 3-4 following a one-time washing in sterile water.
Excessive sterilization adversely affect the formation of shoots and plant growth. After sterilization apical and lateral buds about 0.5 mm in length were planted in the culture medium. Explants started to grow, increase in size in the axils of leaves appeared small lateral buds. For better growth and development of kidneys and increase the rate of breeding they must be over 14-15 days transplanted to fresh culture medium without finishing their sterilizing substances.
After many observations and numerical experiments proved the best modified II Ilienko environment Hamburg. The main components of this environment is macro- and microelements adding 0,05-0,5 mg / l naftylotstovoyi acid 100 mg / l mezoinozytu, 0.3 mg / l thiamine, 0.3 mg / l pirodyksynu 0.5 mg / l nikotynaminu, 45 g / l sucrose; pH before autoclaving should be 5.8. in some cases, to the rapid and massive regeneration plants and added to the nutrient medium 0,05-0,2 mg / l 6-benzylaminopuryna.
Add to the nutrient medium naftylotstovoyi acid (NOC) and benzylaminopuryna (BAP) reduces induction brunkoutvorennya and encourages the formation kalusiv at the base of the stem. This phenomenon occurs when placing the fresh environment leaves. With further replanting of kalusiv in culture medium with a minimum number of 6-benzalaminopurynu hiberelinovoyi and acid regeneration occurs buds and stems.
Pieces of stem size 1.0-1.5 cm with two axillary buds basal part of a vertically placed Busi- agar culture medium to a depth of 0.3-0.5 cm. Cultivation was carried out at a temperature of 26-28 0 C, relative humidity - 70% Lighting - 3-6 kilolyuks. For 14-hour photoperiod light source were fluorescent lamps, the spectral composition of which is close to daylight with low heat radiation.
Axillary buds in such conditions is well developed, vydovzhuvalasya central bud. The massive formation of roots observed already after 5-7 days after explantation buds, and after 14 days, regenerated plants were ready for transplantation. The upper part zrizuvaly plants and transplanted to a fresh culture medium, continuing the process of reproduction. To fast reproduction using apical buds from the upper internodes weaker developing plants with small narrow leaves that are poorly rooted.
Plants form a strong root system and aboveground mass with 6-8 pairs of leaves. Cultivation of explants provides an opportunity to grow both in one flask of 10-12 pc. plants. After 20-25 days with a new bulb explants treated with 40-60, which again landed on fresh culture medium. The lower part of propagated plants developed root system transplanted to specially prepared substrate for rearing and obtaining seedlings.
Sometimes it was necessary for culturing meristem native environment: for rehabilitation and restoration of plant material in the absence of high-agar and to achieve a high multiplication factor, sometimes reaching 50 to 200 plants regenerants from one plant.
For this purpose, tested the mineral composition of the nutrient medium Murasihe-Skuha and Hamburg for the same vitamin and hormone part and concluded that the liquid medium is better meristem growth in the medium-Skuha Murasihe. Developed two versions of the nutrient medium, different phytohormones content in the following ranges: gibberellin acid - 0.5-1 mg BAP - 0.1 mg. Fedulova acid - 9-18 mg and? dose macro- and micronutrients. Meristem (top bud seedlings) were planted in test tubes or flasks of liquid medium. Within 15-20 days culturing meristem growing in kuschopodibni plants with lots of buds. In the allocation of such explants were observed vitrification plant, plants take root well as liquid and on the agar medium. For better root meristem transferred to Hagar Busi- environment. But the root system of plants grown in liquid medium trohty weaker than those that developed on the agar medium.
Use of cell cultures, tissues and organs Stevia speeds up the selection process and increases its efficiency, provides fast reproduction and recovery of valuable genotypes, makes it possible to conduct selection at the cellular level and ensures the preservation of the gene pool.
b) Growing Stevia seedlings from materials obtained in culture in vitro
Obtained by in vitro culture material when it transferred directly into the ground almost all (95-97%) dies. This is too delicate root system of plants grown on agar medium and vegetative parts of the plants grown in glass flasks. Therefore it was necessary to develop technology rearing seedlings of culture in vitro, which could develop in the open field.
For planting and growing of plants obtained by culture in vitro, primarily preparing the substrate of perlite and sand in a ratio of 3: 1. In the cooked mixture made batteries as solutions or making fertilizer in solid form and mix well with the substrate. The height of the substrate must be at least 8 cm. In substrate. Which prepared on the basis of perlite, for planting and cultivation of stevia can use soil, perlite dosypayuchy top layer thickness of 1.5-2 cm. The roots of plants planted in the top layer of perlite, well developed there, then gets into the soil. But unlike the loosened substrate, perlite, sand and compacted soil and root system when transplanting seedlings dropped. Therefore, when growing seedlings in the soil is necessary to provide separation plants (tapes, peat pots, etc.).
Before planting the plants grown in vitro, carefully inspect and discarded infected plants. As well as plants with underdeveloped root system, with broken stems, dried and blackened axillary buds. For better engraftment of the stem of the plant zrizuvaly second internodes from the root to the plant on the left two pairs of leaves. Leaf blade circumcised 2/3 sheet, resulting in decreased their area. Decreased transpiration engraftment and upgraded plants. many roots as ukorochuvaly if they exceed the length of 2.0-2.5 cm. Plants were planted under the scheme 5h4 or 5x5 cm. After planting well-watered and covered with plastic transparent film to maintain high humidity. Humidity substrate maintained at 50%. After 8-10 days after planting gradually accustomed to the environment, opening film for a few minutes.
Gradually increased hardening period, and after 5-7 days of film or glass removed completely. The later started hardening, the longer and harder the process took place. But tempering should take place gradually and carefully, avoiding tasks or drying of leaves.
When growing seedlings spent feeding plants. The first feeding was conducted through 25,030 days after planting, and the next - every two weeks using a solution of NPK fertilizer at the rate of 3 grams of fertilizer per 1 liter of water. For these dressings increased the concentration of the solution. Fertilizing seedlings in rows conducted using pipet. If you use a funnel for feeding, to avoid burns their reduced concentration of the solution. After fertilizing plants well watered. When growing seedlings lighting should be 12-14 kilolyuks with 16-hour light period. By enabling environment already at 12-14 days after planting the plants is intense root. After two to three weeks can be done nipping plants, which causes the growth of side shoots. After 50-60 days seedlings are usually ready for planting in open ground. Plant height at the time reached 7-14 cm plants had 8-14 leaves, internodes 5-7, 1 to 4 stalks and well-developed root system.
Technology rooting green cuttings and seedlings are growing with stevia
Due to the fact that stevia seeds mature enough in our zone it propagated vegetatively, using seedlings on a one-year cycle.
The method of propagation by cuttings green stevia was one of the most effective.
When growing stevia on a one-year cycle must pay great attention to the preparation and storage of rhizomes as breeding material for vegetative propagation. Before collecting stevia (cut its aerial parts) was carried removal and destruction of sick and weakened plants infected by various fungal diseases. When harvesting the stem is cut so that their height to rhizome remained at least 5 cm. Excavation and preparation for winter storage roots performed at temperatures below 5 0C. digging out roots, they were taken from them, which formed many healthy kidneys. Rhizomes after digging gently (so as not to damage the root system) was separated from the ground and made into a box at the bottom of which poured 3.5 cm of wet earth uniformly covered from above ground, slightly compacting it. The root system must be closed povnistyu earth, and above the surface is only part of the stems.
Roots kept in the basement at 5-8 0 C and optimal humidity of 85%, and substrate moisture during storage should be 17-20%.
After winter storage roots in mid-February survey, the percentage determine their safety, remove damaged and transferred to a greenhouse or other space with a temperature of 20-25 0C. lighting kilolyuks 8-9. Healthy roots with living kidney transplanted into another container manufactured from a mixture of fresh and well watered. Under these conditions, kidney regrowth was 10-15 days. For cuttings zrizuvaly tops of young shoots. Size 6-7 cm cuttings with two or three internodes. Cuttings for planting should cut so that the shoot remain mizvuzla least one pair of leaves. Then with axillary buds formed two shoots, which later can also be used for cuttings.
Cutting cuttings is best done in the morning when trkanyny plants have more water. When harvesting cuttings should not be allowed and drying them pryvyalennya. Keep the cuttings to the next day is unacceptable, because they lose money, turn black and become unusable for planting. Cuttings planted in wet, relatively sterile and controlled substrate consisting of perlite and sand to a depth of 1.5-2 cm with the distance between 4-5 cm and between rows - 5-6 cm. The depth of the substrate layer should not be less than 8.7 cm. Depth of the day before landing disinfects 0.01% solution KmnO4.
Heat - a mineral of volcanic origin, which includes 70-75% silica, about 10-15% alumina, 1.5-2.0% iron oxide and small amounts of calcium and magnesium oxides.
In thermal processing mineral turns into a homogeneous porous material used as a growing medium in hydroponics, the propagation by cuttings and to improve the structure of heavy soils.