Scientific basics of adaptive technology of growing stevia in Ukraine

Abstract

Problem statement. Specialization and concentration of production are the main direction of the genetic potential realization in new stevia varieties.

The technology of growing stevia, as well crop production technology in general, includes a system of agronomic techniques and material support aimed at the production of competitive products along with the preservation and restoration of soil fertility. The nature of technology is generally limited by the achievement of scientific and technical progress and the level of development of productive resources, economic, social and demographic characteristics of the country, region, and specific farm. In this regard, to ensure high productivity of stevia, a complex of agronomic measures aimed at providing the optimal and reduced cost of labour and costs per unit of production is required.

Review of recent research and publications. Monitoring of stevia introduction in Ukraine shows that the most suitable for growing regions are the following: Autonomous Republic of Crimea (yield of green mass 0.2−37 t/ha and dry matter 0.6−3.7 t/ha), Transcarpathians (7−27 t/ha and 0.25−2.7, respectively), Polissia (0.2−37 t/ha and 0.6−3.7 t/ha, respectively) and Central Forest-Steppe (5−30 t/ha and 0.2−3.4 t/ha, respectively).  According to the environmental assessment of varieties carried out in 2010−2012 yrs, the most intensive and plastic variety appeared to be Berehynia [2,4].

The most common multiplication way is vegetative method implemented through cultivating seedlings in vitro or green cuttings; however, these methods are considerably labour-consuming.

The method of propagation with seeds is much cheaper, but the difficulty is that seeds are very small, elongated, and spindle-shaped, with the 1000-seed weight of 0.4 g, laboratory germination index of 60−70% and field germination 26−2.7% [1.3].

There are known data on the close correlation between the seeding timing and field germination: the correlation coefficient is 0.96 and 0.07. The treatment of stevia seeds using the solution of microelements helps to increase field germination by 11.5% compared to the control treatment [5].

The purpose of the research was to determine agronomic and economic efficiency of growing stevia as affected by agronomic and technical factors, soil and climatic conditions of a particular region.

Materials and methods. In the Institute of Bioenergy Crops and Sugar Beet, a new method of stevia multiplication has been developed (Patent for Utility Model No: 119472, September 25, 2017, bulletin No: 18).

The purpose of the utility model is to improve the way of multiplication by fixation of stimulated seeds to a water-soluble tape at the rate of 40 seeds per 1 m of tape  followed by the recommended technology of placing the tape in the field. This will contribute to a significant increase in dry yield of stevia leaves, as well as reduce costs per production unit.

The problem is solved in the following way: seeds are soaked in warm water from 60 to 90 min, dried, mixed with dry sand and sown in early spring; according to the suggested utility model, stevia seeds are soaked in a solution of microelements for 24 h, dried and fixed to a water soluble tape at the rate of 40 seeds per 1 m of tape. Prepared tape should be placed in the soil in late May. It is important to maintain soil moisture at the 70−80% level of the least field moisture capacity.

Thus, distinctive (new) signs in interaction with the known ones provide the detection of a new property of the technical solution, namely: the maximum realization of the biological potential of stevia plants obtained as a result of multiplication which manifests itself in a significant increase in the yield of green mass and dry leaves (Table 1).

On the average of 2012−2014 (data of Slavutych variety), the leaf area in stevia agrophytocenose increased 41.6%, plant density at the time of harvesting increased from 102,700 pts/ha (control treatment) to 110,200 pts/ha (proposed method). Green mass yield increased 55.5% and dry mass yield 64.2% compared to the control treatment. A similar trend (the most developed plant and the highest crop productivity) was noticed when growing new generation stevia varieties. To illustrate, leaf area of the agrophytocenose increased, on the average of 2015-2017 (data of Halyna variety), 38.5%, stand density at the time of harvesting increased from 105,300 pts/ha (control treatment) to 114,200 pts/ha (proposed method), green mass yield from 15.5 to 21.7 t/ha and dry mass yield from 1.51 to 3.60 t/ha, respectively.

The degree of plant development as well as plant density is subject to weather conditions during the seeding-emergence period and vegetation period of stevia. Thus, in moderately dry 2012, in Central Forest-Steppe, Hydrothermal coefficient (HTC) fluctuated within the range of 0.6−0.7, field germination was 25%; in moderately humid 2013 and 2014 yrs, HTC fluctuated from 2.4 to 0.9 and  2.4 to 1.2, field germination was 36% and 44%, respectively.

The duration of the emergence period along with the field germination index indicates the domination of weather conditions factor during the seeding-emergence period: HTC was 2.0 and higher compared with HTC 0.6−0.7.

The most developed stevia plants were obtained in 2014: the height ranged from 57.0 to 57.6 cm, the number of stems from 3.2 to 3.6, the number of shoots from 8.3 to 9.8, the assimilation surface of plants from 1790 to 1412 cm²; HTC during the growing season fluctuated from 0.9 to 1.2. In the Northern Steppe (Kherson region) in the period from 2012 to 2014, the highest productivity of stevia agrophytocenose was observed in 2011, 2013 and 2014. Stand density at harvesting being 91,000−95,000 pts/ha the yield of green mass made up 25.2−30.4 t/ha, dry mass 2.51−3.03 t/ha at the HTC during the growing season ranging from 0.8 to 1.0 and from 1.0 to 0.7, respectively.

The recommended method of stevia multiplication combined with using new varieties (Halyna, Maryna, Kateryna) provides high agronomic and economic efficiency (Table 2).

The annual economic effect of the implementation of the proposed method on the area of 3.5 ha in the Kherson region was UAH 180,200.

Conclusions

1. In Ukraine, agronomical and economical potential of stevia is not fully used in farming. In the system of measures purposed to the implementation of biological potential of modern stevia varieties, the introduction of technologies adapted to regionally-specific soil and climatic conditions (agronomical techniques and weather conditions) is of special importance.

2. To obtain the yield of dry leaves of stevia at the level of 3.5−4.0 t/ha it is recommended:

- to grow stevia in the regions where 460–560 mm precipitation per year is available, including 322−460 mm during the growing season; moisture reserves in 100-cm soil layer must be 150−180 mm, accumulated temperatures during the period of active vegetation 2450−28000 ºC and HTC 0.8−1.3;

- to grow domestic varieties, such as  Berehynia, Slavutych, Halyna, Maryna, Kateryna

- recommended method for stevia multiplication: Patent for Utility Model No: 119472 (reg. September 25, 2017).