Morphological Features of Plants and Yield of Sunflower Hybrids Cultivated in the Northern Part of the Forest-Steppe of Ukraine

In Ukraine, a sunflower is the main oil crop from which more than 90% of vegetable fats are produced. An increase in production is due to the expansion of cultivation area, which necessitates research on sunflower hybrids adaptability in the northern regions of Ukraine, where in recent decades, there has been a significant change of weather conditions and which may be favorable for its cultivation. The research was carried out in the Northern part of the Forest-Steppe of Ukraine on light loam chernozems. Reaction to growing conditions of four hybrids was studied by establishing the stability and plasticity of hybrids in terms of yield formation due to changes in morphological characteristics of plants. Yield potential realization is high enough, which is provided by sufficient amounts of positive, active, effective temperatures and precipitation. Calculation of the coefficients of plasticity and stability allows identifying stable sunflower hybrids, hybrids with a high level of plasticity, and recommending them to production. The yield of early-maturing hybrid Ukrainskyi F1 increases rectilinearly with plant density increasing (r = 0.977 0.998), while hybrids P63LL06 (r = 0.651 0.882); NK Ferti (r = 0.589 0.846), and NK Brio (r = 0.689 0.804) form a higher yield at standing densities up to 60 thousand plants per hectare, and with further thickening, the yield decreases. With the thickening of sowings, the height of all hybrids plants increases (r = 0.97 0.99), and there is a decrease in the number of seeds per anthode, and the weight of 1000 seeds. Sunflower hybrids can be divided into the groups according to the peculiarities of yield formation due to morphological features: 1) yield increases only due to sowings’ thickening— Ukrainskyi F1; 2) combined efficiency-increasing sowings’ density to 60 thousand plants/ha and generative organs formation—NCKBrio; 3) hybrids of intermediate type—NK Ferti and P63LL06. How to cite this paper: Kalenska, S., Ryzhenko, A., Novytska, N., Garbar, L., Stolyarchuk, T., Kalenskyi, V. and Shytiy, O. (2020) Morphological Features of Plants and Yield of Sunflower Hybrids Cultivated in the Northern Part of the Forest-Steppe of Ukraine. American Journal of Plant Sciences, 11, 1331-1344. https://doi.org/10.4236/ajps.2020.118095 Received: July 10, 2020 Accepted: August 22, 2020 Published: August 25, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
Global change of climate and weather conditions, growing needs of mankind for food, energy plant resources, raw materials for industrial processing, and other urgent human needs requires crop production expansion [1] [2] [3] [4] [5]. At the same time, crop production should be economically and environmentally feasible. In recent years, Ukraine has been expanding the production of an important oil crop of universal use-sunflower [6]. The sown areas of sunflower (Helianthus annuus)-a traditional culture of the Steppe zone are actively moving to the Northern regions of Ukraine [7]. Establishing of hybrids' adaptability, peculiarities of their productivity formation, dependences of vegetative and generative organs formation, depending on weather and technological factors is relevant.

Significance and State of Sunflower Production
Sunflower is a crop that is widespread in the southern regions of Europe and Ukraine in particular. In recent years, due to significant changes in weather conditions-increasing in air temperature, and a prolongation of the period with air temperatures above 8˚C -10˚C in the northern regions, there has been an expansion of the geographical zone of sunflower cultivation. Establishing the features of sunflower cultivation and development of adaptive cultivation technologies is an important area of research for the northern regions of Europe and Ukraine [8].
In Ukraine, the main oil crop is a sunflower, which produces over 90% of vegetable fats. Gross sunflower production in Ukraine has increased to 12 million tons in recent years. Between 2010 and 2019, the area under sunflower in Ukraine increased by almost one and a half million hectares and reached 6.1 million hectares. Ukraine is a leader in sunflower production and the largest exporter of sunflower oil in the world-5, 6 million tons (57% of total exports in 2018). The gross harvest of sunflower seeds increase was mainly due to the expansion of sown areas. A feature of the soil-climatic zone of the Steppe of Ukraine, where sunflower is mainly grown, is an insufficient amount of precipitation with a significant potential of solar energy. Due to such natural features, almost every year there is an acute shortage of soil moisture, which prevents the planned level of yield [9]. With high plowing levels of soils and oversaturation of crop rotations by sunflower, specific diseases and pests are spread. All this necessitates research on the adaptability of sunflower hybrids in the Northern regions of Ukraine, where in recent decades there has been a significant change in

The Adaptability of Sunflower Plants to Growing Conditions
The task of creating and implementing in production hybrids with high yield potential with optimization of growing conditions is complicated by the problem of ecological adaptation: the potential of production conditions can't grow adequately to the growth of genetically determined yield potential of varieties [10] [11] [12]. The ability to economically and efficiently use environmental factors is a highly adaptive genotype property [13]. The adaptability of hybrids is an extremely important feature of variable abiotic and biotic environmental factors [14] [15]. Sunflower is a culture of the temperate zone and is quite flexible to weather and soil conditions [16] [17]. Sunflower is a salt-tolerant crop [18]. Sunflower is characterized by high adaptability and yield [8]. Optimally formed plant population of sunflower influence the quality of seed for processing [19] [20].

Morphological Features of Plants, Sunflower Yield Depending on Plants' Density
The level of varieties' and hybrids' biological potential realization depends on both-growing technology and climatic conditions of a particular year and their interaction [21] [22] [23] [24]. Sunflower yield is determined by several factors, among which the role of hybrid and plants' standing density are among the determinants [25] [26]. Agrocenosis formation with an optimal plant density and optimal nutrients supply provides an increase in its productivity [27] [28]. Morphological characteristics of the plant are varietal characteristics, but under the influence of environmental factors and cultivation technologies, they may change [29]. Under the influence of nitrogen fertilizers, a yield increase of sunflower hybrids, an increase in the anthode diameter was recorded [30] [31] [32]. The height of plants with plants standing density increasing usually increases, especially with using irrigation [33]. There is also a decrease in the weight of 1000 seeds and seeds number from the anthode [34]. However, with plant density increasing, competition for light between plants increases, which leads to a decrease in vegetative and reproductive plasticity of the plant [35], while lower plant density leads to reduced light absorption by plants what leads to a reduction in yield per unit area [36] [37] [38]. Theoretical studies and practical experience have shown that high yields per unit area are usually associated with low plant competitiveness due to reduced anthode diameter, plant biomass, weight of 1000 seeds, seed yield per plant, unsaturated fatty acids [39] [40].

Conditions and Methods of Research
In the Northern part of the Left Bank Forest-Steppe of Ukraine (Bakhmach, Chernigiv region (51.1513819, 32.8623028)) during 2016-2018 field studies were conducted for the identification sunflower hybrids of different ecotype by mor-American Journal of Plant Sciences phological characteristics, stability, and yield plasticity under variable weather conditions. Multifactor field experiment was based on the following scheme: factor A-"hybrid": "Ukrainskyi F1", "P63LL06", "NK Brio", "NK Ferti"; factor B-"density of plants' standing": 50, 55, 60, 65 thousand pieces/ha. The area of the accounting plot is 50 m 2 , repeating is quadruple.
In the experiment, hybrids of different selection were used, which differ in growth intensity at the initial microstages of development, which requires additional research for sunflower cultivation in the northern regions of Ukraine: Ukrainskyi F1 (selection of Ukraine)-an early-ripening hybrid-develops rapidly in the initial microstages.
P63LL06 (selection of Pioneer)-a medium-early-ripening hybrid with sufficiently high growth energy at the initial microstages.
NK Brio (selection of Syngenta)-a medium-ripening hybrid-early in its maturity group. Initial growth is slow.
NK Ferti (selection of Syngenta)-a medium-ripe hybrid with medium growth energy in the initial stages.
Originators of hybrids give recommendations on plant density, but depending on weather conditions and soil, hybrids respond differently to crop density, so identifying the optimal crop density of a particular hybrid is extremely important. For the study, we chose a step to change the density of standing plants with a difference of 5 thousand plants/ha from the density recommended by the authors of hybrids.
The soil of experimental plots is light loam chernozem with humus content 2.98%. The reaction of soil solution is close to neutral, pH-5.9 -6.2. The weighted average content of mobile forms of phosphorus is 132 mg/kg of soil, exchangeable potassium is 94 mg/kg of soil, the content of exchangeable calcium and magnesium is increased, respectively 10.6 and 2.2 mg-eq/100 g of soil. Soil quality-69 points, and therefore in general the soil of the experimental area has favorable agrophysical properties and relatively high natural fertility, which allows growing sunflowers successfully.
The field was plowed to a depth 28 -30 cm, and after plowing, for weeds destroying and leveling the soil, cultivation to a depth 8 -10 cm was used. In the spring-soil moisture conservation by spring harrowing. Fertilized by anhydrous ammonia-123.3 kg/ha in the nitrogen active substance; under pre-sowing cultivation was applied N 16 P 38 P 58 in the active substance. During sowing, a complex fertilizer N 8 P 24 K 24 S 5 , in the active substance, was applied in the row area.
Soil herbicide Primextra TZ Gold 500 was applied at the rate 4 l/ha. Fungicide Propulse at the rate 1 l/ha with simultaneous application of YaraVita BORTRAC 150 at the rate 1 l/ha was used for prevention diseases. The sunflower hybrids were sown in the third decade of April: April 20th; April 22nd; April 25th, respectively, in 2016, 2017, 2018. Seedlings in all three years of research appeared on May 2-3. Hybrids reached full maturity (15% of seed moisture) in the last decade of August-after August 25th. The sunflower was harvested with 7% of seed moisture in the I -II decade of September. American Journal of Plant Sciences Determination of stability and plasticity of hybrids by yield was performed according to the Eberhard-Russell method, while for the criterion "point" we used the criterion "weather conditions of the year" [41]. In this modification, we determined the stability and plasticity of the hybrids relative to the meteorological conditions of the research site.
Sunflower yields were accounted for each site by combine harvesting.
Statistical data processing was performed using the software package SAS 9.4.

Weather Conditions of the Research Region
The climate of the district is temperate-continental. The average temperature in July is +20˚C. The average January temperature is between −6˚C and −8˚C. The

Structural Components of Sunflower Hybrids' Yields
The yield of sunflower hybrids significantly depends on plants' standing density and this is the predominant factor in yields' formation. The individual yield of plant decreases due to crop thickening, but due to the increase of plants' number in the area, the yield also increases.
Reaction to the sowings' thickening was manifested through a change in the yield structure. The early-maturing hybrid "Ukrainskyi F1" formed a lower yield compared to other hybrids ( Table 2).  (Table 3).
Hybrid "NK Brio" in all years of research and at different densities stood the highest yields (Table 4).
The hybrid formed anthodes with the largest diameter among the studied hy- Hybrid "NK Ferti" yielded slightly relative to the yield of hybrid "NK Brio" (Table 5). According to the morphological features, plants of hybrid "NK Brio" However, these connections are not as close as in the hybrid "Ukrainskyi F1".

Correlative Dependence of Hybrids' Yield and Sowing Structure
With a positive correlation between yield and plant density, we found an inverse

Discussion
Studies show growing of sunflower hybrids in the Northern part of the Forest-Steppe of Ukraine is highly efficient. Yield potential realization is quite high, which is provided by the necessary amounts of positive, active, and effective temperatures and sufficient precipitation. Determining the coefficients of plasticity and plasticity allows us to identify stable sunflower hybrids, hybrids with a high level of plasticity and to recommend them for production in the growing regions. Adaptive technological factors cause increased stability of yield's sunflower hybrids.

Conclusions
Due to the formation of sunflower agrocenosis with optimal plant density provides an increase in its productivity.
Sunflower hybrids can be divided into several groups, according to the peculiarities of yield formation: 1) yield increases only due to sowings thickening-Ukrainskyi F1; 2) combined efficiency-due to increasing the density of sowings up to 60 thousand plants/ha and generative organs formation-NK Brio; 3) hybrids of intermediate type-NK Ferti and P63LL06.
The optimal density of early-maturing hybrids plants standing is not less than 65 thousand pieces/ha and of medium-ripe hybrids-the optimal density-60 thousand pieces/ha.