1. Introduction
One of the main tasks of introduction work with ornamental plants is to identify the most promising taxa for introduction into the practice of green construction and use in breeding. A special approach requires conducting such studies on varieties with high decorative qualities. This is due to the fact that in some cases these varieties may not fully display decorative features in the new conditions. Conducting research on variety studies and variety evaluation makes it possible to identify the most promising varieties for this region, which show their biological, decorative, and economically valuable properties as much as possible in the new conditions [1].
Hibiscus syriacus L.—is of great interest because of its high decorative properties and resistance to adverse environmental influences. If the first varieties appeared 200 years ago, today, according to some sources, their number is close to 4000 [2]. In the United States, Canada, France, Italy, Germany, China, South Korea and Japan [3] [4] [5], extensive research is being conducted to create new varieties of this plant. Currently, 2 forms and 10 varieties are grown in Uzbekistan.
Many works are devoted to the introduction assessment [6] [7] and variety evaluation of ornamental plants [8] [9]. Scientific sources provide special scales for evaluating [10] [11] [12] some types of ornamental shrubs [13] [14] [15]. In the conditions of the Krasnodar Territory, the assessment of economic and biological indicators and decorative qualities of 15 varieties of Syrian hibiscus was carried out [16].
Purpose of the Study
The purpose of this work was to conduct a complex estimation of the varieties of H. syriacus L. in the conditions of Tashkent (Uzbekistan).
2. Materials and Methods
The objects of research were 2 forms and 10 varieties of H. syriacus L. of various origins. Of these, 2 varieties with a double type of flower. The study included 7 summer plants. The number of registered plants of each variety is not less than 10.
The 100-point Timkin scale (2011), based on a modification of the methods Bylova and Zalevskaya, was used for variety evaluation. Each trait was evaluated on a 5-point scale, then indexed by the significance coefficient of this trait. At the same time, considering the assortment and climatic conditions of Tashkent, we increased the significance coefficient of the flower stability attribute due to the “originality” attribute.
When considering the economic and biological qualities, a 50-point scale was used and considered the productivity of flowering, resistance to diseases, winter hardiness, and drought resistance.
3. Result and Discussion
For an objective assessment of the results of the introduction work for each studied variety, it is advisable to allocate primarily decorative indicators. When evaluating ornamental crops, the decisive role belongs to qualitative indicators (color, shape), determined by subjective impressions [17].
Among the numerous varietal characteristics that determine the decorative value of the variety, the color of the flower occupies a special place. The uniqueness of the general tone or a peculiar shade, saturation, purity and color stability contribute to the rapid recognition and wide distribution of the variety [18]. When assessing the color of the Syrian hibiscus flower, considering the requirements for creating a flower garden and the mentality of the population of Uzbekistan, the high score estimated the white, pink and red colors of the flower.
In the conditions of Tashkent, the flowers of the Luce, Totus Albus varieties with a diameter of 8 - 9 cm were rated 3 points. The other varieties received high scores for this indicator.
On the basis of the shape of the flower of the variety Russian Violet and Totus Albus, for the bell shape, they received 4 points each. The flowers of the other varieties have a flatter, regular, rounded shape.
The lateral parts of the petals of the corolla Luce and Rubis touch less than 2/3. At the same time, the Luce flower has a large number of petals and petaloids. In other varieties, the edges of the petals overlap each other and form a beautiful rounded shape. The flower of the Speciosus variety is anemonic.
In the conditions of Tashkent, the flowers of all the studied varieties received high ratings for their resistance to external environmental factors.
In terms of decorative qualities, the form with a white flower and the Speciosus variety received the highest rating (Table 1). The purple flower shape and the Red Heart,Woodbrige, Pink Giant and Luci varieties also scored over 75 points. The flowers and leaves of these varieties are very decorative. They bloom profusely. These varieties are more resistant to high summer temperatures.
The decorative qualities of Aphrodite,Pink Flirt,Russian Violet,Totus Albus and Rubis varieties were rated from 60 to 75 points. According to the shape and size of the flower, the addition of petals, the shape of the bush and the abundance of flowering, these varieties have lower indicators. These varieties were included in group 2.
Among the studied varieties, there were found different varieties belonging to the 3rd group for decorative qualities.
Along with the high requirements for the decorative qualities of the studied varieties in the formation of an assortment for mass reproduction, the importance of evaluating and selecting varieties based on their economic and biological properties increases. The most important task is to evaluate varieties based on such characteristics as flowering productivity, resistance to diseases and pests, and resistance to adverse environmental conditions [18].
Both forms and varieties Speciosus, Red Heart, Russian Violet and Woodbrige received high ratings on the flowering productivity index (Table 2). The flowering productivity of Luce, Pink Flirt and Aphrodite varieties was average.
In the conditions of the Western Ciscaucasia, varieties of Hibiscus syriacus L. are affected by fungi of the genus Septoria sp., Phyllosticta sp., Alternaría sp., as well as by the Hibiscus yellow vein mosaic virus (Timkina). In the conditions of Tashkent, such damage was not observed. But in all varieties except Luce, Pink Flirt, Rubis and Russian Violet, Heliothis armígera L.—cotton scoop and Aphis
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Table 1. Evaluation of decorative qualities of introduced varieties of Hibiscus syriacus L. (Tashkent, 2019).
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Table 2. The results of the assessment of the economic and biological qualities of varieties of Hibiscus syriacus L. in the conditions of Tashkent (2019).
malvae Koch—mallow aphid were found. But these pests imperceptibly affected the decorative and biological qualities of the varieties.
The introduction of plants outside the range is limited, first of all, by temperature indicators, and then by other environmental factors [19]. In winter hardiness, the variety Speciosus is superior to all others. Aphrodite, Pink Flirt and Rubis are less stable. In severe winters, these varieties have damage to annual shoots. The remaining varieties occupy an intermediate position.
The critical weather factors for introduced plants in the conditions of Uzbekistan are high temperature and low humidity in the spring-summer period [19] [20]. In the varieties Aphrodite, Luce, Pink Flirt, Rubis, Russian Violet and Lotus Albus, more than 30% of the plants were damaged by the stress factors of the summer period. In the remaining varieties, damage was observed in less than 30 % of the plants.
According to economic and biological characteristics, the studied varieties were divided into 2 groups: 1—received more than 40 points; 2—received 30 - 40 points. Both forms and varieties of Pink Giant, Red Heart, Russian Violet, Speciosus and Woodbrige were included in the first group. At the same time, the Speciosus variety received the highest rating. The second group includes all other varieties.
As a result of a comprehensive assessment, 3 groups of varieties were identified (Table 3):
Group I—the most promising varieties-received more than 125 points-both forms and the Speciosus variety;
Group II—promising varieties-received 110 - 124 points—Luce, Pink Giant, Red Heart, Russian Violet and Woodbrige;
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Table 3. Results of a complex estimation of varieties of Hibiscus syriacus L. in the conditions of Tashkent.
Group III—fewer promising varieties—received less than 109 points—Aphrodite, Pink Flirt, Rubis and Totus Albus.
4. Conclusions
Thus, we can assume that the soil and climatic conditions of Tashkent are quite favorable for the cultivation of Hibiscus syriacus L., and all the varieties we have studied can be used in landscaping. The plant is widely used as a landscape. The highest rating score was given to the Speciosus variety, which is in good agreement with the data that plants of this variety show their decorative qualities well even under such negative environmental influences as high temperature, lack of moisture, and high insolation [17].
The most promising—both forms and the variety Speciosus are characterized by better adaptability. Promising varieties—Luce, Red Heart, Russian Violet in a short time were able to adapt to new conditions, and were able to maintain their decorative and biological qualities. Pink Flirt, Rubis and Totus Albus are among the less promising varieties. These varieties were introduced to Uzbekistan in recent years and have not yet been able to fully adapt. The group of less promising varieties also includes Aphrodite. Although it was introduced in the last century, it could not sufficiently show decorative and economic and biological qualities in the conditions of Tashkent.