TY - JOUR AU - Trotsenko, V. I. AU - Zhatova, H. O. AU - Yatsenko, V. M. AU - Kolosok, I. O. PY - 2021/10/12 Y2 - 2024/03/29 TI - INFLUENCE OF RETARDANTS ON PLANT GROWTH AND SUNFLOWER YIELD STRUCTURE JF - Bulletin of Sumy National Agrarian University. The series: Agronomy and Biology JA - ab VL - 43 IS - 1 SE - Articles DO - 10.32845/agrobio.2021.1.8 UR - https://snaubulletin.com.ua/index.php/ab/article/view/421 SP - 55-64 AB - The results of laboratory and field experiments to study the reaction of sunflower plants to the use of retardant Moddus are covered in the article. The research was carried out within the the program for the development of variety model for the conditions of the North-Eastern Forest-Steppe and Polissya of Ukraine, (state registration number of 0116U001506).This program was implemented in 2016–2020 at the Institute of Agriculture of North-Eastern Ukraine and Sumy National Agrarian University In an experiment with pot culture of sunflower, it was found that the treatment of seeds with retardant provided a reduction in the length of the hypocotyl from 35.4 ± 3.60 to 24.52 ± 2.80 mm. In the anatomical structure there was a decrease in cell prosenchyme from 7.1 to 4.6 and an increase in cell wall thickness from 2.4 ± 0.21 to 3.1 ± 0.28 μm. According to the results of changes in the anatomical structure of the plant hypocotyl , it was determined that the maximum level of stem contraction due to the reduction of cell prosenchyma was about 30 %. In the conditions of a field experiment with a wedge-shaped arrangement of rows, changes in stem height and yield formation algorithm depending on the level of intraspecific competition were investigated. The study was conducted in the density range from 20 to 160 thousand pieces plants / ha, variants with seed treatment, treatment of vegetative plants, and combined use of retardant were studied, Seed treatment with Moddus provided statistically significant reduction in plant height only in areas with minimum level of intraspecific competition. The highest effect of reducing plant height – from 209.3 to 166.5 and 159.8 cm - was observed in areas with maximum sowing density (160 thousand plants / ha) in variants with treatment of vegetative plants in the phase of 8–10 leaves or with complex treatment according to the scheme “seeds + phase of 8–10 leaves”. It is established that the actual level of stem height reduction is determined by the phase of plant development and the level of intraspecific competition in sowing. The effect increased with the combined use of retardant and with increasing plant density. The factor of yield reduction was changes in the structure of plant productivity, accompanied by a narrowing and shifting of the range of indicators of optimal sowing density. ER -