Symbiotic Efficiency and Cytokinin Activity of New Mesorhizobium cicerі Strains

The efficiency of the introduction of nodule bacteria, microsymbionts of legumes in agrocenoses, largely depends on the activity of biologically active substances’ biosynthesis by diazotrophs. Seed bacterization with effective rhizobia strains capable of synthesizing exometabolites for phytostimulating activity not only promotes the formation and functioning of symbiosis but also creates the conditions for increasing plant resistance to adverse environmental conditions. The aim of the work was to research the symbiotic activity, efficiency and ability of chickpea rhizobia new strains to biosynthesize phytohormonal exometabolites of cytokinin nature. Methods. Microbiological, physiological, cytological, biochemical, and physicochemical. Results. New strains of Mesorhizobium ciceri ND-101 and Mesorhizobium ciceri ND-64 were shown to have different symbiotic activity. The efficiency of inoculation of Skarb chickpea seeds with bacterial suspension of Mesorhizobiu mciceri ND-101 was at the same level with the industrial strain of Mesorhizobium ciceri H-12. Bacterization of Mesorhizobium ciceri ND-64 increased the chickpea roots nodules by 69%, their weight by 74%, and nitrogenase activity by 73% relative to the positive control (inoculation with Mesorhizobium ciceri H-12), as well as increased chickpeas yield by 22%. It was established that Mesorhizobium ciceri ND-64 strain exhibits the highest cytokinin activity in the bioassay. Cytokinins in the total amount of 174.94 μg/g of completely dry biomass were detected in the culture medium of Mesorhizobium ciceri ND-64, which is 53% higher than that of Mesorhizobium ciceri ND-101 strain and 99% higher than that of Mesorhizobium ciceri H-12 strain. Conclusions. Mesorhizobium ciceri ND-64 strain with high nitrogen-fixing activity and symbiotic efficiency is capable to synthesize a relatively high amount of extracellular cytokinins. The high concentration of cytokinins indicates their important role in the formation and functioning of nodules, as they stimulate the proliferation of root tissues and, in this way, have a positive effect on the chickpea productivity.