This article presents methods for determining the drought resistance of plants at different stages of development. To determine drought resistance at the early stages of plant development, when creating breeding material, it is necessary to use the most accessible and common laboratory methods, which include modeling moisture deficit in solutions with increased osmotic pressure, which consists in the ability of germinated seeds of a variety to use low moisture reserves in the soil and predict resistance genotypes to soil moisture deficiency in the early stages of ontogenesis. At various stages of plant vegetation, recently, indirect assessment of drought resistance using physiological methods is becoming increasingly common. The most informative are methods of studying the water regime of leaves, namely: determination of tissue hydration, water deficit and water-holding capacity of leaves. Leaf water loss reflects the water status of plants and is key to their survival in drought conditions. The indicator of water-holding capacity characterizes the plant's ability to resist dehydration for a more or less long time, the length of which depends on its level. The water status of the plant is determined by the water deficit, which is an important indicator of drought resistance. Watering plants indicates that they are supplied with water, which is necessary for the flow of biochemical reactions (that is, for vital activity) and is one of the important indicators of the water regime of plants. The water content in the leaves indicates the attitude of the plants to the lack of moisture. To differentiate genotypes by drought resistance, various selection indices are used, based on the productivity of plants in optimal and stressful conditions for the selection of drought-resistant genotypes.

The problem of increasing the production of winter barley grain on irrigated lands can be solved thanks to the improvement of the varietal composition, optimization of sowing dates and improvement of the nutrition system, in particular through the use of drugs with growth-regulating properties. Taking into account the important biological role of growth regulators in the plant nutrition system, the aim was to determine the influence of Gummifield Forte brix, MIR and PROLIS on the content of nitrogen, phosphorus and potassium in the main phases of plant development of different varieties of winter barley at optimal and late sowing dates. The research was conducted at the Institute of Irrigated Agriculture (now the Institute of Climate-Oriented Agriculture) of the National Academy of Sciences according to methodological recommendations for conducting field tests under irrigation conditions. In the above-ground mass of plants, straw and grain, the total content was determined: nitrogen – according to Kjeldahl, phosphorus – according to Murphy-Reilly, potassium – using a flame photometer. It was determined that on the irrigated lands of the South of Ukraine, the use of growth regulators Gumifield Forte brix, MIR and PROLIS had a significant effect on the accumulation of the main nutrients (especially nitrogen) by plants and winter barley grains. The highest content of basic nutrients in plants was at the early stages of development (spring tillering), after which their amount decreased until the end of the growing season of the crop. The maximum nitrogen content of 2.02% on dry matter on the Dev'iatyi val variety and 1.85% on the Academichnyi variety was provided by the use of Gummifield Forte Brix.Among the varieties, the Dev'iatyi val, on average, accumulated nitrogen in the grain for sowing on October 1 and 20 by 9.1 and 9.5 percentage points more than Akademichnyi, according to the plant growth regulator factor. Thanks to the treatment of winter barley seeds with plant growth regulators Gumifield Forte Brix and PROLIS and sowing the crop at the optimal time, it is possible to increase the nitrogen content in plants and grain by 6.0-15.1 and 9.3-22.5 percentage points, respectively, which will have a positive effect on grain formation and its quality. In further studies, it is necessary to optimize the application doses of mineral fertilizers using new multi-component growth regulators of winter barley plants under irrigation conditions in the South of Ukraine

Resistance to stress factors is of great natural and ecological importance, since the ability of plants to adapt to the conditions of existence is one of the factors that determines the range of distribution of species and cultures. In this regard, there is a growing need for an accurate assessment of the adaptive potential of plants, which is impossible without studying the physiological bases of their resistance and developing agrotechnical, selection-genetic, and genetic engineering methods for increasing the resistance of cultivated plants to abiotic stresses using new fundamental knowledge about the mechanisms of resistance. Adaptability of each variety is reflected in numerous adaptive reactions, which collectively make up the adaptive potential of the genotype. Each adaptive reaction, in turn, reflects the reaction of the entire biological system to changes in the environment through the links of morphogenetic effects that complete the formation of a specific feature of the plant, and selection for survival is an adaptive process, a kind of compensation for such adaptation is a decrease in potential and actual seed productivity. This article presents the methods of determining environmental stability, plasticity, with the help of which it is possible to classify varieties according to the type of direction of cultivation: intensive, stable and plastic.