Influence of growth regulators on the sunflower growth and development in the Northern Steppe of Ukraine

Topicality. In addition to mineral and organic fertilizers, microfertilizers and plant growth regulators should be used more widely to eliminate negative factors (excessive man-made load, deterioration of water, nutrient regimes and soil humus condition) and to improve the sunflower nutrition system. Issues. Growth regulators intensify the development of the leaf surface, activate the basic life functions of sunflower plants: membrane processes, cell division, respiration and nutrition, enzyme systems activity, photosynthesis, and create a branched root system with enhanced absorption capacity. Purpose. To study the influence of growth regulators with different action on the morphogenesis, sunflower growth and development and productivity of different maturity groups in the Northern Steppe of Ukraine. Materials and methods. The field trials were established and carried out in accordance with generally accepted methods of research.. The experimental part of the work was performed during 2018–2020 in the research field of the National Research Center at the Dnipro State Agrarian and Economic University in the stationary experiment of the Crop Production Department in five-field crop rotation: clean fallow – winter wheat – maize – barley – sunflower. Spraying sunflower plants with growth regulators Vympel K-2 (0.7 l/ha), Architect (0.5 l/ha) and Ce-ron (0.5 l/ha) was carried out in the 6–8th pair of leaves stage. Results. When the growth regulators were applied, plant height of sunflower reduced, but such indicators as leaf surface area, chlorophyll content in the leaves, head diameter and number of seeds per head, thousand seed weight, seed yield and quality increased. y. Conclusions. The maximum leaf surface area of sunflower (up to 70.9–78.1 thousand mІ/ha, or 5.5 –10.2 % more than the control) was observed when growth regulator Ceron was applied at the dose of 0.5 l/ha. In this case, sunflower plants formed the largest heads with diameter of 23–26 cm (11.5–30.4 % more than the control), and the maximum number of seeds per head was 863–925.3 pieces that exceeded the control by 3, 4–5.6 %. The highest thousand seed weight (54.0–60.0 g) was for the mid-early hybrid Sumico HTS, and the lowest (51–55 g) – for the mid-late Subaro HTS that is explained by the biological characteristics of the hybrids. The crop yield increased by 1.05–1.17 times due to the application on sunflower of plant growth regulators. The largest increase in grain yield for all hybrids (0.22–0.27 t/ha, or 13.5–14.8 %) was provided with Ceron (0.5 l/ha). The application of Ceron (0.5 l/ha) and Architect (0.5 l / ha) growth regulators increased oil content by 3–8 and 4–6 percentage points, respectively. Keywords: sunflower, hybrids, growth regulators, leaf surface area, chlorophyll, yield, seed quality.