Varietal features of development and performance of Brassica Juncea L. according to growth regulators in terms of the Forest-Steppe of Ukraine

Abstract

The rationale for choosing the research topic. Mustard is a crop of multivector industrial significance due to its diverse uses. The seeds of Brassica Juncea L. contain 41-48 % of high-quality oil for technical and food purposes. Modern trends of global climate change and more frequent occurrence of stressful situations determined the urgency of using plant growth regulators to stabilize the development of mustard. It is also worth noting that no study of the mechanism of the growth regulators’ effect in terms of a controlled environment on the growth and development of mustard plants has been conducted, which makes the research data particularly relevant. The scientific novelty of the obtained results. Comprehensive research was first conducted to study the influence of growth regulators on the growth and development of Brassica Juncea L. in a controlled environment (climate chamber) and field conditions. The antioxidant enzymatic activity and the mechanism of morphological adaptation of roots and shoots of mustard seedlings under artificially created conditions of drought and salinity were first investigated. Varietal features of brown mustard performance were identified using growth regulators in terms of the forest-steppe of Ukraine. The technology of growing brown mustard is optimized for the conditions of the forest steppe of Ukraine. The issue of the influence of weather and stress conditions on the features of growth, development, and performance according to the variety and the combined use of growth regulators for seed treatment and foliar application have been further developed. The economic and energy efficiency of the cultivation of brown mustard with the use of the studied elements of the technology has been substantiated. The practical significance of the obtained results. The technology of growing brown mustard was recommended for production, which ensured a seed yield capacity of 1.77 and 1.85 t/ha, accordingly. The main elements of the research were tested in the production and implemented on the farms of the Sumy and Poltava regions, in particular, at the Elita and Rodina 2017 farming enterprises on a total area of 60 hectares. Their efficiency has been confirmed, namely: net operating profit – 1345 and 1420 UAH/ha; profitability of production – 59.5 and 65.3 %, accordingly. The dissertation provides theoretical generalizations and a new solution to the scientific issue of stabilizing the impact of stress factors and increasing the performance of Brassica Juncea L. The research technology is based on the study of the combined use of growth regulators for seed treatment and foliar application in terms of the forest steppe of Ukraine. The world’s scientific developments regarding the identification of optimal methods and types of application of growth regulators for brown mustard plants have been analyzed. Under current climate changes and the emergence of stressful conditions, the combined use of growth regulators for seed treatment and foliar application have been proven to be an important reserve for stabilizing the development and increasing the performance of Brassica Juncea L. The response of mustard seedlings to abiotic stresses and the efficiency of modern plant growth regulators were studied in the climate chamber of the Henan Scientific and Technical Institute of Science and Technology (PRC). Salt and drought stresses are the most common abiotic stresses that suppress plant growth and reduce performance or even cause plants’ death. To some extent, plant growth regulators can reduce plant inhibition during stress. The salt adaptive mechanisms of mustard seedlings and roots were studied by determining their growth parameters, biomass, photosynthesis, MDA content, and some key antioxidants. Mustard seedlings were treated with four salt concentrations (0, 50, 100, and 200 mM NaCl). The results of calculations carried out with the help of Epson Perfection V800 Photoscanner (Epson, lnc., LongBeach, CA, USA) showed that the treatment with 200 mM NaCl significantly inhibited the growth of shoots, causing a decrease in leaf area, as well as dry and fresh matter. The inhibitory effect of salt on shoots correlated positively with the decrease in chlorophyll content and performance index and correlated negatively with MDA content in leaves. Increasing salinity has been shown to have a positive effect on root growth. The ratio of the number of lateral roots of the first order and the density of lateral roots were higher than those of the control group by 26.1 %, 28.7 %, and 58.5 % on day 10, accordingly. MDA levels remained unchanged. The coordination of antioxidant enzymes ensures the high efficiency of plants in removing NPK. These results persuade that the antioxidant system is involved in the adaptive regulation of root growth to avoid the deleterious effects of high soil salinity. In the second laboratory experiment, the brown mustard variety (Brassica Juncea L.) of Felicia was used to analyze the response and compensation effects of growth and physiology under drought stress and rehydration at the seedling stage. The seedlings were exposed to different levels of drought stress (0, 10%, 15%, and 20% PEG). Growth parameters, fresh weight, chlorophyll fluorescence, and antioxidant system were measured. The processed results showed that drought stress suppresses the growth of roots and shoots (WinRHIZO 2007, Regent Instruments. Inc., Quebec, Canada) and reduces the performance of the photosystem (a portable fluorometer PEA, Hansatech Instruments Ltd, King'sLynn, UK was used). After rehydration, root length and plant fresh weight increased rapidly, and the performance index (PIABS) was higher compared to the control, indicating a compensatory effect. Chlorophyll content as determined by DualexScientific (Force-A, Orsay, France) decreased significantly under moderate and severe drought stress. However, it increased under mild stress. After rehydration, chlorophyll content under moderate and severe stress did not return to control levels, and there was no significant difference between mild stress and control. During drought stress, the activity of antioxidant enzymes and MDA content in leaves increased significantly. After rehydration, MDA and antioxidant enzyme activity were higher than in the control group, especially under moderate and severe stress. According to the results, mustard is highly adapted to moderate drought stress due to the effective activity of antioxidant enzymes and photosynthesis, as well as its rapid recovery after rehydration. The third experiment aimed at evaluating the effect of plant growth regulators (PGRs) on the germination rate and seedling morphology of two varieties of blue mustard (Brassica Juncea L.) (Felicia and Prima) under simulated conditions of drought stress using PEG-6000. The application of PGRs contributed to the growth of seedlings under drought stress conditions but did not have a noticeable effect on the germination rate of both varieties. Raw mass and root length, leaf area, stem length, and volume of the Felicia variety significantly increased by 24.28 %, 3.3 %, 24.7 %, 19.4 %, and 30.9 % under Antistress treatment. Besides, the number of lateral roots reached its maximum with the use of Agrinos and Regoplan compared to plants without PGR under drought conditions, which were 135.55 % and 121.20 %, respectively. For Prima, the application of Fast Start had a significant effect on raw root weight, total root length, the number of lateral roots and main root length, root surface area, and leaf area and stem volume by 17.62 %, 18.12 %, 211.20 %, 53.75 %, 28.57 %, 15.9 %, and 32.3 %, accordingly. The results of the field research conducted during 2019-2021 in terms of the Left-Bank Forest-Steppe of Ukraine showed that the use of PGR affected the height of plants, the number of branches, the area of the leaf surface, the number of pods, seed yield capacity, and the weight of 1000 seeds of both varieties. This study demonstrated that a combination of seed treatment and foliar spray was effective in promoting mustard growth compared to a single seed treatment or foliar spray. The seed yield capacity of the Felicia variety (1.78 t/ha) was significantly higher than that of Prima (1.67 t/ha). The maximum yield capacity for Prima was obtained on the variants of complex application of Fast Start (1.76 t/ha) and Regoplan (1.77 t/ha); for Felicia it was Agrinos (1.89 t/ha) and Antistress (1.91 t/ha). All plant growth regulators increased the average weight by 1000 pcs. seeds of both varieties. For Prima, the influence of Fast Start and Regoplan on the weight of 1000 seeds had the maximum effect (9.5% compared to the control). Except for Albit and Vermistim D, other growth regulators increased the weight of 1000 Felicia seeds by 5.8-11.7 %. The use of growth regulators increased the average oil content of Brassica Juncea L. seeds by 1.18-5.61%. A significant effect on the oiliness of seeds in the Prima variety, determined with the help of an infrared analyzer (SupNir 2700, China), was due to the use of Agrinos, Fast Start, and Regoplan. There was no significant difference in the seed oiliness of the Felicia variety by the factor of “Method of application of PGR” and “Type of PGR”. In terms of protein content, no difference was found between the two varieties, as well as methods and types of growth regulators used. According to the results of the correlation analysis, seed yield capacity had positive and close (p<0.01) correlations of individual mean values with the number of pods, number of branches, leaf surface area, and seed weight per plant. The weight of 1000 seeds was closely correlated (p<0.01) with chlorophyll content and plant height. These results showed that the number of branches, individual plant performance, the number of pods, and the leaf surface area were the main factors that determined the yield with inherent varietal features of the response to the application of plant growth regulators. Oil content correlated negatively with protein. The analysis of economic and energy efficiency indicators revealed that the cultivation of brown mustard (Brassica Juncea L.) in the Left-Bank Forest-Steppe of Ukraine is expedient. For brown mustard, the maximum level of profitability (149%) and energy efficiency ratio (2.75) was obtained for the cultivation of the Felicia variety and foliar fertilization with the growth regulator Regoplan.