Soybean is one of the most profitable advanced crops in agricultural production in Ukraine and the world as a whole. Therefore, studies of means of regulation and increase in the adaptive capacity of soybeans in symbiosis with nodule bacteria under the action of unfavourable environmental factors are relevant and should be aimed at the use of complex bacterial compositions involving modern nanotechnological approaches. Nanocarboxylates of ferrum, molybdenum and germanium metals were used as components of rhizobia inoculation suspension for soybean seed treatment to study the effectiveness of their complex effect on the regulation of the activity of the key antioxidant enzyme superoxide dismutase in plants under drought. Various symbiotic systems were used, which included soybean plants and inoculation suspensions based on the active, virulent Tn5-mutant Bradyrhizobium japonicum B1-20 by adding nanoparticles of ferrum, germanium and molybdenum carboxylates to the culture medium in a ratio of 1: 1000. Citric acid was the chelator. A model drought lasting 14 days was created during the period of active fixation of atmospheric molecular nitrogen by root nodules of soybeans in the budding and flowering stages, by means of controlled watering of plants to 30% of the total moisture content. In the stage of bean formation, watering of plants was resumed to the optimal level – 60% of the total moisture content. The control was soybean plants, the seeds of which were inoculated with a suspension of rhizobia without the addition of chelated metals. The following research methods were used in the work – microbiological, physiological and biochemical. According to the results, it was found that when nanoparticles of carboxylates of ferrum, molybdenum and germanium were added to the inoculation suspension of rhizobia, there was an increase in superoxide dismutase activity in root nodules and a decrease in soybean leaves under optimal water supply conditions of plants. This indicates the initial changes in the activity of the antioxidant enzyme in these symbiotic systems, induced by the influence of chelated metals in combination with the rhizobia of the active Tn5-mutant B. japonicum B1-20. Prolonged drought induced an increase in the overall level of superoxide dismutase activity in soybean nodules and leaves, compared to plants grown under optimal watering conditions. The symbiotic system formed by soybeans and B. japonicum with molybdenum carboxylate nanoparticles was the most sensitive to long-term drought exposure, compared to two other soybean-rhizobial symbioses using ferrum and germanium nanocarboxylates. This was manifested in the unstable reaction of the enzyme to the action of drought – suppression or intensification of the level of its activity in the root nodules and leaves of soybeans inoculated with rhizobia containing molybdenum carboxylate nanoparticles. In symbiotic systems with the participation of germanium and ferrum nanocarboxylates, slight changes were revealed in superoxide dismutase activity in root nodules and leaves of plants during drought and restoration of enzyme activity to the level of plants with optimal watering after water stress. It is concluded that the addition to the culture medium of rhizobia Tn5-mutant B1-20 of nanocarboxylates of germanium or ferrum is an effective means of regulating the activity of the antioxidant enzyme superoxide dismutase in soybean root nodules and leaves, which can contribute to an increase in the protective properties and adaptation of plants to the action of dehydration.

Objective. Evaluate the efficiency of soybean inoculation with pesticide-resistant nodule bacteria Bradyrhizobium japonicum under the influence of pre-sowing seed dressing with Maxym XL,Standak Top and Fever and preventive spraying of plants with the fungicide Akanto Plus. Methods. Physiological, microbiological, gas chromatographic, vegetation experiment, statistical.Results. The number and weight of nodules formed on soybean roots during the growing seasonunder the action of the prothioconazole-based fungicide Fever were reported to be lower comparedwith the control and other variants of experiment. Pesticides Maxym XL and Standak Top had a lesspronounced toxic effect on the formation of legume-rhizobial symbiosis with the participation offungicide-resistant B. japonicum B78 Tn5 mutant compared to Fever. A decrease in the level of N2assimilation by 10.9–41.1 % in the three-leaf phase was found with the combined use of seed pesticides and nodule bacteria included in the study, relative to the variant with inoculation only. However, during the growing season, the negative effect of fungicidal preparations on the functioning oflegume-rhizobial symbiosis decreased. Conclusion. Under the conditions of the model vegetationexperiment with the concomitant use of Standak Top and Fever and bacterization, a decrease in individual plant productivity by 7.0 and 14.1 %, respectively, has been reported. The complex actionof the pesticide Maxym XL and inoculation with pesticide-resistant B. japonicum B78 transposonmutant, contributed to the maximum increase in yield by 27.2 %. The obtained data confirm the expediency of selection of fungicides and nitrogen-fixing microorganisms for concomitant use to ensure high economic and protective effects.

Insufficient water supply is one of the main factors that significantly reduce the activity of nitrogen fixation by legume-rhizobial symbiotic systems. That is why comprehensive research on aspects of their resistance to water stress and the search for scientifically substantiated ways to improve the existing ones and develop modern, competitive technologies of growing legumes in arid conditions are becoming especially relevant. The aim of the work was to investigate the processes of formation and functioning of soybean-rhizobial symbiotic systems developed under conditions of different water supply and influence of nanocarboxylates of cobalt, ferum, germanium, chromium, сuprum and molybdenum. The nanoparticles of specified metal nanocarboxylates were used as components of the inoculation suspension of rhizobia of Tn5 mutant B1-20 for soybean seed treatment. A model drought lasting 14 days was created by controlled irrigation. Microbiological and physiological research methods were used in the study. We determined that insufficient water supply caused a significant decrease in the nodulation potential of rhizobia and the intensity of molecular nitrogen fixation by symbiotic systems formed with the participation of soybean plants and nodule bacteria without adding these metal nanocarboxylates to the inoculation suspension. Application of most of the metal nanocarboxylates used as components of the inoculation suspension mitigated the negative impact of stress on the investigated parameters. The study revealed the stimulating effect of cobaltnanocarboxylate on the activity of molecular nitrogen fixation, which was more pronounced in the conditions of insufficient water supply. Symbiotic soybean systems formed with the participation of nodule bacteria containing germaniumcarboxylate nanoparticles were proved to be the least sensitive to the negative impact of insufficient water supply. This was indicated by high rates of nodulation and nitrogen-fixing activity compared with other studied symbiotic systems. We confirmed that the addition of chromium nanocarboxylate to the inoculation suspension of rhizobia provided the highest rates of nodulation and nitrogen-fixing activity of soybean root nodules under optimal growing conditions and, at the same time, had no noticeable positive effect under water stress. We determined that сuprum and molybdenum nanocarboxylates, as components of the inoculation suspension, regardless of the water supply level, had a less notable positive effect on the processes of nodule formation and nitrogen fixation, and in some cases even led to a decrease in the investigated values for control plants. Thus, the study demonstrated that the use of germanium, cobalt and ferum nanocarboxylates as components of the bacterial suspension helped to increase the adaptation of the formed legume-rhizobial symbiotic systems to water stress, as evidenced by the maximum indexes of nodulation and molecular nitrogen fixation in the context of insufficient water supply and recovery of their level to optimal after the stress influence had ended. Based on the results, it was concluded that inoculation of seeds by the complex bacterial preparations made on the basis of Bradyrhizobium japonicum B1-20 with a content of germanium, cobalt and ferum nanocarboxylates in the concentration of 1:1000 can become one of the important means in soybean growing technologies of increasing the nitrogen-fixing potential and resistance of plants to insufficient water supply.

The intensity of drought-induced oxidative processes by the degree of superoxide anion radical generation and the activity of NADPH oxidase in soybean associated with different activity and virulence of Bradyrhizobium strains were studied. The importance of active Bradyrhizobium japonicum for the formation of effective symbiosis with soybean to improve the realization of the adaptive potential of plants during drought and post-stress period has been established.Increased NADPH oxidase activity in nodules (by 3.5 -4.7 times), as well as excessive production of superoxide radical in nodules (by 1.5 -2 times) and roots (from 113 to 323%) of soybean in symbiosis with efficient Bradyrhizobium strains were observed during drought. However, the development of oxidative processes in effective soybean-rhizobial symbioses slowed down after exposure to stress. This indicates the adaptation of soybean plants associated with active Bradyrhizobium strains to growing conditions. In symbiotic systems with ineffective Bradyrhizobium strains, a significant increase in NADPH oxidase activity in nodules (by 3.3 -6.0 times) and intensification of superoxide radical formation in nodules (by 2 -3 times) and roots (from 260 to 330%) recorded both under drought and post-stress period. This indicates a significant development of oxidative processes and the inability to realize the adaptive potential of soybean plants in symbiosis with ineffective Bradyrhizobium strains. Thus, excessive formation of the superoxide radical and an increase in the activity of NADPH oxidase indicate the appearance of oxidative processes, which are a typical reaction in response to drought in soybean-rhizobial symbioses of varying efficiency. At the same time, the development of oxidative processes depends on the ability of soybean plants in symbiosis with Bradyrhizobium japonicum to realize their adaptive potential in during drought and post-stress period.

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