A total of 110 strains of nodule bacteria was isolated from plants Onobrychis transcaucasica and Onobrychis chorassanica. Nodulation study of bacteria in both Onobrychis plant species in microvegetation experiment gave a very low nodulation on plant roots. The intensive nodulation of Onobrychis plants was recorded in vegetation experiment and for Onobrychis transcaucasica the efficiently-nodulating strains were found OT102, OT103, OT117, OT121, OT130, OT136, ОT139, ОT140, while for Onobrychis chorassanica plants—ОC106, ОC107, ОC109, ОC112, ОT103, ОT117 and ОT123 strains. Nucleotide sequencing of the 16S rRNA gene and BLAST analysis showed that nodule bacteria of Onobrychis plants were related to Rhizobium, Burkholderia, Enterobacter and Pantoea genera. It has been shown a possibility of growing up of Onobrychis plants at minimal additional moisture of sabulous soils in the Kyzyl Kum Desert, creating artificial pastures and thereby immobilizing the desert blown sands

To search for an alternative to alfalfa under conditions of salinity and drought, a comparative study was carried out to explore the effect of salinity on the symbiosis of alfalfa and local esparcet species (<i>Onobrychis transcaucasica</i> and <i>Onobrychis chorassanica</i>) inoculated with their nodule bacteria. The salinity of up to 30 mM NaCl insignificantly affected the biomass growth of shoots and roots of alfalfa plants, but the increase in the salinity from 30 to as high as 140 mM NaCl led to the biomass decrease. The salinity produced a double effect on the nodulation process in inoculated alfalfa plants as follows: 1) at 30 - 100 mM NaCl the stimulation of nodulation and increased leghemoglobin activity were observed; 2) at salinity concentrations higher than 100 mM NaCl the suppression of both nodule formation and leghemoglobin activity was observed. Alfalfa plants under inoculation with the <i>Sinorhizobium meliloti</i> 10 strain obtained a considerable resistance to salinity (50 - 80 mM NaCl). The efficient symbiosis of <i>O. transcaucasica</i> plants with <i>Rhizobium</i> sp. OT111 and <i>O. chorassanica</i> plants with <i>Rhizobium</i> sp. OC109 enhanced the adaptation of plants to salinity up to 150 mM NaCl. The gradual growth suppression of both Onobrychis plants species started from 200 mM NaCl, and salinity concentration 300 mM NaCl was critical (sublethal) for plants independently of inoculation by nodule bacteria. In field conditions, <i>O. chorassanica</i> was more resistant to salinity than <i>O. transcaucasica</i>, but minimal irrigation for both species of <i>Onobrychis</i> showed a higher effect on their growth and development than the moderate salinity at the concentration 75 mM NaCl. The lower limit (drought threshold) of drought-resistance of <i>Onobrychis</i> plants was 6% - 8% of soil humidity. In shoot and roots of alfalfa, both <i>Onobrychis</i> plant species subject to salt stress, aldehyde oxidase and xanthine dehydrogenase enzymes and different number of their isoforms as well as their electrophoretic mobilities/activities were found

From nodules of perennial xerophyte desert leguminous plants – Ammodendron conollyi, Astragalus villossimus, Astragalus unifoliolatus – 151 bacterial isolates have been isolated. The study of nodulation showed that AC8-1, AC11, AC21, AC1-1, AC12-1 isolates (from Ammodendron conollyi), AV1, AV8-1, AV9, AV26-1, AV36-1 isolates (from Astragalus villossimus) and AU17-1, AU30-1, AU30-2, AU20-1, AU23 isolates (from Astragalus unifoliolatus) formed an effective nitrogen-fixing symbiosis with the host plants. As a result of 16S rRNA gene study of the salt-resistant nodule bacteria it has been determined that bacteria were related to Rhizobium, Burkholderia and Achromobacter genera. The study of isolates growth has revealed that there were fast-growing and moderately-grow- ing isolates that possessed with doubling-time varying from 20 to 45 min. Their examination for antibiotic-resistance showed that the number of bacterial colonies of selected strains decreased to some extent in the presence of chloramphenicol, but in all strains the resistance to antibiotics was detected. The further investigations of resistance of the formed symbiosis to stresses (drought, salinity) showed that at 6.41% of moisture the maximal height and biomass of inoculated plants of Ammodendron conollyi were 21 cm and 2320 mg, but at 3.8% moisture the height reduced by 4 times (up to 4.5 cm) and the biomass – by 11 times (203 mg). The analogous effect was observed in Astragalus villossimus and Astragalus unifoliolatus symbiosises. The salinity equal to 100-200 mM NaCl did not affect practically on normal growth and development of desert leguminous plants symbiosis, while for Astragalus villossimus such affecting concentration comprised up to 100 mM NaCl. The light microscopy and electron microscopy of Astragalus villossimus nodule sections showed that V1 nodule bacteria strain efficiently colonized the internal space within nodules, where they were transformed into bacteroids. At 100 mM NaCl salinity concentration the colonization of nodule bacteria within nodule plant cells reduced in comparison with control nodules of plants grown in non-salted conditions