INDICATORS OF PHYSIOLOGICAL CHARACTERISTICS OF THE LINES IN SOYBEAN UNDER OPTIMAL AND DEFICIT IRRIGATION CONDITIONS

ABSTRACT

The article reveals the results of the analysis of physiological-transpiration rate, leaf water retention, total water content, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content in the lines of the soybean gene collection grown under conditions of optimal water supply (control) and water stress (experiment). As a result of the experiment, the physiological traits of the leaves of soybean specimens, such as transpiration rate, water retention features, total water content, chlorophyll a, chlorophyll b, total chlorophyll and carotenoids, were found to be varying and decreasing in terms of water deficiency. The soybean lines Genetic 35 and Sochilmas were found to be more physiologically resistant to water stress than other lines.

АННОТАЦИЯ

В статье представлены результаты анализа показателей физиологической транспирации, влагоудержания листьев, общего содержания воды, содержания хлорофилла а, хлорофилла b, общего хлорофилла и каротиноидов в линиях коллекции генов сои, выращенных в условиях оптимального водоснабжения (контроль) и водный стресс (эксперимент). В результате эксперимента было обнаружено, что физиологические характеристики листьев образцов сои, такие как скорость транспирации, характеристики влагоудержания, общее содержание воды, хлорофилл а, хлорофилл b, общий хлорофилл и каротиноиды, изменялись и уменьшались в терминах. дефицита воды. Было обнаружено, что линии сои Genetic 35 и Сочилмас более физиологически устойчивы к водному стрессу, чем другие линии.

Keywords: soybean, water regime, water deficit, total chlorophyll, chlorophyll “a”, chlorophyll “b”, carotenoids, resistance.

Ключевые слова: соя, водный режим, дефицит воды, общий хлорофилл, хлорофилл «а», хлорофилл «b», каротиноиды, устойчивость.

Introduction

At the present the world’s growing population is leading to an increase in demand for the main agricultural crops including soybeans and other products in many countries, along with food sources. Obtaining high quality products, improving the yield and other valuable economic traits and characteristics of the created varieties are the most important tasks in the world today and in genetic and selection research great attention is paid to the extensive use of soybean gene pool samples.

Due to the growing negative impact of global climate change on agriculture, determination of genotypic responses of primary sources to water stress by physiological traits and the interrelationship of these traits in the studies conducted on the creation of varieties resistant to various extreme conditions, including drought, based on the study of genetic, physiological and valuable economic indicators of soybean is of great scientific and practical importance.

The limited water resources and the increasing scarcity of water in recent years require the study of the selection value of collection sources, like other areas, for the development of the theoretical substantiation on the creation of drought-resistant varieties. The Action Strategy for the further development of the Republic of Uzbekistan sets the task of "creating new varieties of agricultural crops adapted to local soil-climatic and ecological conditions". In fulfilling this task, it is important to determine the genotypic response of soybean varieties and lines to water stress by their physiological and morphological traits and to study the physiological characteristics of adaptation to water stress, to prepare valuable materials for genetic selection study on drought tolerance and to apply them in the breeding.

The most important factors: stresses, environmental conditions, and their changes affect the plants and constantly decrease crop growth and development and crop yields around the world (1).

Water deficit or water stress is one of the factors that negatively affects productivity and is regarded as a risk to effective crop production. Drought (water stress) resistance trait of a crop is an important feature associated with productivity. To improve this trait, thorough measures and changes are required in the complex of relevant traits in selection work, and the resulting trait is called drought resistance (2).

Drought is one of the most important environmental stresses limiting crop yields and productivity in most parts of the world, especially in warm and dry areas (2).

Chlorophyll is one of the major chloroplast components essential for the process of photosynthesis (3,4). Decreased chlorophyll content under drought stress is a common symptom of pigment photo-oxidation and chlorophyll degradation (5,6). The decrease in chlorophyll content in drought stress depends on the duration and degree of drought (7,8). A decrease in total chlorophyll content as a result of drought stress means a decrease in the yield potential. Since the production of reactive oxygen types is mainly due to the absorption of excess energy in the photosynthetic apparatus, this can be prevented by the breakdown of these absorbing pigments (6,9). If we consider the effect of water deficit on chlorophyll a and chlorophyll b in leaves, we can say that water stress is a step that leads to protein breakdown due to hydrolysis of these chloroplastic proteins, reducing of leaf pigments and chlorophyll loss (10).

From the point of view of plant physiology, drought, which causes stress in plant growth and a 50-30% decrease in yield due to low humidity, occurs by high evaporation and high temperatures of sunlight (11), also high temperatures cause drought stress to the respiration, photosynthesis, and enzyme activity of the plant. Drought and the light reaction of photosynthesis due to the sun, and the continuous production of free radicals of oxygen leading to the destruction of plants is light and oxidation. Nutrients absorbed from the upper horizon of the soil, which are present in many foods, are reduced due to drought (12). Increased drought conditions, accumulation of salts and ions in the upper layers of the soil around the root cause osmotic stress and ionic toxicity (poisoning). The first response to stress is a biophysical effect. Indeed, as drought stress increases, the cell wall of a plant begins to dry out or loosen, the pressure also decreases as the cell volume decreases, and the cell’s growth potential decreases leading to the growth rate decreases depending on the potential pressure. These factors also affect the size and number of leaves in the plant (12). Leaf mesophyll cells become dehydrated due to drought. The amount of abscisic acid stored in the chloroplasts in the protective cells is used up, and the formation of ABA in the protective cells and mesophyll is increased. With the increase of ABA, potassium and calcium are released from the protective cell. As a result of the stomatal closure of this process, water loss is observed in the protective chamber. Due to lack of water, the rate of photosynthesis in plants decreases. This occurs because of a decrease in photosynthetic enzymes. Due to lack of water, discoloration occurs on the leaves and trichomes and stomata spread on the leaf surface. Under severe water deficit, the roots shrink and the leaves begin to shed (12,13).

The research aims to distinguish physiologically resistant genotypes to water deficiency (stress) by studying water-related traits and the amount of chlorophyll pigments in the leaves of soybean plants under different water regime conditions.

RESEARCH OBJECT  AND METHODS

As a research object, Genetic 35, Sotilmas, Genetic 18, Genetic 15, Genetic 37, Orzu, Genetic 30, Genetic 39, Genetic 24, Genetic 31, Genetic 1, Genetic 8 foreign and domestic varietal samples in “Valuable object” soybean collection of the Institute of Genetics and Plant Experimental Biology were used.

The research was conducted in the field of Zangiota Experimental Base in Zangiota district of Tashkent region, affiliated to the Institute of Genetics and Plant Experimental Biology of the Academy of Sciences of the Republic of Uzbekistan in 2020-2021. This area is located 20 km from Tashkent, in the upper reaches of the Chirchik River, at an altitude of 398 meters above sea level. The climate is characterized by strong heat in summer (June, July, August) and a sharp drop in air temperature in winter (especially in December and January). Sunny days are 175-185 days, frost-free period is 200-210 days. Precipitation is observed in autumn, winter and spring, and the air is dry in summer, which requires watering the soybean. The soil of the experimental field is a typical gray soil, low in humus, moderately sandy in mechanical composition. The land slope is weak, unsalted, weakly damaged by wilt. Groundwater is deep (8.0 meters and more). Soil moisture field capacity is 22%, bulk density – 1.32-1.33 g / cm³.

During the years of the project, the experimental field was irrigated according to the 1-2-1 scheme and the total volume of water was 4800-5000 m³ / ha. This allowed the soil moisture to be kept at an optimal level, i.e. 70% -72% relative to the limited soil moisture field capacity (LSMFC). The agro-technical measures applied during the years of the experiment allowed to ensure good growth and development of plants.

Soybean under variety testing were planted on field on the territory of the institute and grown under conditions of optimal water supply and water deficit. The volume of water used for irrigation was measured on the ZENNER ETC equipment and 5200 m³/ha of water was consumed against the background of optimal supply and 3800 m³ /ha against the background of water deficit. In order to determine the physiological parameters of water exchange in plants of soybean lines planted in different water regimes under field conditions, the 3rd leaf on the main stem, calculated from the growth point of 10 typical plants on each line, was used in the experiment. The total amount of water in the leaves was determined according to the methods by Tretyakov N.N. (1990), water retention of leaves by Kushnirenko M.D. (1970), transpiration rate by Ivanov A. A. (1950), the amount of chlorophyll pigments was determined by the methods of Lichtenthaler H. K. and Wellburn, A. R. (1983).

The numerical parameters obtained for each trait were statistically processed by the dispersion analysis method (Dospekhov, B.A. 1985) to prove whether the difference between the lines and varieties was reliable or unreliable using the Fisher criterion, and the smallest difference (LD₀₅) rate was detected at 95% degree of reliability.

RESULTS AND DISCUSSION

During the field experiments on soybean crops, the transpiration rate in the samples of 13 varieties and gene collections of soybeans was studied under conditions of water stress and optimal water supply. At the same time, Genetic 15 (510.8 ± 9.79 mg) and Sochilmas (478.8 ± 5.06 mg) varieties were found to have high transpiration rates under conditions of optimal water supply. High transpiration rate under water deficiency condition was noted in Genetic 18 (333.78 ± 5.77 mg) and Genetic 15 (328.13 ± 6.75 mg) samples. When performing dispersion analysis in the experiment, the Genetic 15 soybean sample was found to be a water-prone genotype in terms of transpiration rate. In the experiment, Genetic 1 (210.78 ± 3.42 mg) and Genetic 37 (203.1 ± 8.70 mg) samples were found to have the lowest transpiration rate under optimal water supply, while under water deficit condition Genetic 30 (133, 13 ± 6.65 mg) and Genetic 35 (121.5 ± 5.85 mg) samples were found to have the lowest transpiration rate (Table 1).

At the dispersion analysis in the experiment, it was also found that the Genetic 35 soybean sample in terms of transpiration rate was a stable genotype relative to water deficit condition.

When leaf water retention were studied under conditions of water deficit and optimal water supply, the highest result was observed in Genetic 30 (54.8 ± 2.21%) and Genetic 18 (56.2 ± 1.36%) samples under optimal water supply conditions, the lowest indicator was determined in Genetic 35 (36.7 ± 1.37%) and Genetic 24 (37.7 ± 1.67%) samples. Under the water-deficient cndition, the highest rate was noted in the Orzu (30.2 ± 1.77%) variety, while the lowest rate was in the Genetic 35 (17.30 ± 0.91%) sample (Table 1). In the experimental dispersion analysis, it was found that while the Genetic 35 soybean sample was a stable genotype in terms of water retention under water deficit and, the Orzu and Genetic 15 soybean sample were unstable under optimal water supply.

When the total water content indicator was determined, the highest values were found in Genetic 37 (75.99 ± 0.45%) and Genetic 15 (74.5 ± 1.64%) samples under conditions of optimal water supply, while under the conditions of water deficit, Genetic 35 (73,4±0,69 %) sample was found to have higher indicator. In the case of water deficit, the lowest result was noted in Orzu (66.8 ± 1.10%) and Genetic 39 (67.4 ± 0.85%) samples, while in the case of optimal water supply, a lower rate was in Genetic 30 (69.5 ± 0.19%) sample (Table 1). Experiments have shown that while Genetic 35 sample of soybean did not show a sharp drop in total water content indicator under water deficit condition relative to optimal water supply conditions, a sharp drop was noted in Genetic 15 sample. At the experiments it was obvious that in water-related physiological characteristics, such as transpiration rate, leaf water retention, and total water content a decrease has been identified under of water deficit conditions. The transpiration rate, water retention property, and total water content characteristics of Genetic 35 sample of the soybean were found to be more resistant to water stress compared to other varieties and specimens.

When the amount of chlorophyll a was studied, the highest indicator of the amount of chlorophyll a was observed in Sochilmas variety (24.5 ± 0.96mg / g) in the control variant, i.e in optimal water supply condition and the lowest indicator was in Genetic 39 (8.7 ± 0.12mg / g) sample. In the experiment, the lowest indicator was found in Orzu variety (7.1 ± 0.60 mg / g) in water deficit conditions, while the highest rate was found in Genetic 35 (15.3 ± 0.33 mg / g) sample (table 2). When the amount of chlorophyll a in the soybean was studied under different regime conditions, the amount of chlorophyll a in Genetic 35 sample of the soybean collection was stable in water stress compared to other varieties and specimens.

When the amount of chlorophyll b in the control was determined, the highest indicator was noted in Sochilmas (11.31 ± 0.11mg / g) and Genetic 31 (11.72 ± 0.75 mg / g), while Genetic 39 (6.49 ± 0.15mg / g) showed the lowest value. In the experiment, Genetic 35 (8.3 ± 0.43 mg / g) had the highest value, while Genetic 39 (3.6 ± 0.08 mg / g) had the lowest value (table 2).

When total chlorophyll was studied in the leaves of soybean plants, under the optimal water-supply conditions Sochilmas (35.8 ± 1.08 mg / g) and Genetic 15 (32.6 ± 2.79 mg / g) showed the highest indicator, while in water deficiency condition Genetic 35 (23.6 ± 0.76 mg / g) sample showed the highest result.   Under conditions of optimal water supply and water deficit, the lowest values of 15.2 ± 0.07 and 11.2 ± 0.17 mg / g were observed in Genetic 39 sample (table 2). The results of the experiment showed that the Genetic 35 sample of the soybean was found to be more stable than other samples in terms of total chlorophyll content in water stress.

When carotenoid content was studied in soybean varieties and specimens, the highest values under control and experimental conditions were found in Genetic 24 and Sochilmas (5.84 ± 0.40 mg / g; 3.88 ± 0.12 mg / g and 5.78 ± 0.39 mg / g; 3.42 ± 0.12 mg / g respectively) varietal samples. The lowest values under control and experimental conditions were noted in Orzu and Genetic 39 (3.08 ± 0.25 mg / g; 1.79± 0.14 mg / g and 2.18 ± 0.06 mg / g; 1.83 ± 0.11mg / g, respectively) varietal samples (table 2).