Effectiveness of nitrogen-fixing symbiosis of guar (Cyamopsis tetragonoloba) with strains Bradyrhizobium retamae RCAM05275 and Ensifer aridi RCAM05276 in pot experiment

Legume plant guar ( Cyamopsis tetragonoloba (L.) Taub.) is a source of guar gum, a complex of polysaccharides that is used in various industries. This crop is widely cultivated mainly in India and Pakistan, but in recent years there has been an increasing interest in the industrial cultivation of guar in the southern regions of Russia. One of the problems of introducing this culture into Russian agriculture is the absence in the soil of bacteria that can form symbiotic nodules on the roots of guar in the soil-climatic conditions of the Russian Federation. One of the problems of the introduction of this crop into the agriculture of the Russian Federation is the absence of bacteria capable of forming symbiotic nodules on guar roots under environmental conditions of Russia. In the present work, the first data on the efficiency of inoculation with nodule bacteria of guar growing in the soils of Russia were obtained. The aim of this work was to evaluate the effectiveness of promising rhizobial strains of guar Bradyrhizobium retamae RCAM05275 and Ensifer aridi RCAM05276 when growing plants in soils selected in the regions of the Russian Federation and not containing the corresponding nodule bacteria. To inoculate the seeds of guar variety Kubanskiy Yubileiny, inoculums in the form of aqueous suspensions of bacteria were used. Inoculums were obtained according to the standard procedure for the preparation of liquid biopreparations of nodule bacteria. The effectiveness of symbiosis was studied in a pot experiment with growing plants in sod-podzolic soil and chernozem. Inoculation with both strains resulted in active formation of nodules (about 20-40 nodules per plant), while no nodules were found on the roots of control uninoculated plants. The number of nodules per plant was maximal in the variants of inoculation with the strain B. retamae RCAM05275. The values of the total mass of nodules per plant were maximum in the variants of inoculation with the strain E. aridi RCAM05276 due to the formation of larger nodules. The nodules formed on lateral roots had a rounded irregular shape, pinkish color (evidence of the presence of leghemoglobin in them) and significantly varied in size. Both strains increased the biomass of shoots and the whole plant by about 70% when growing plants on sod-podzolic soil and chernozem, but did not affect the biomass of the roots. The inoculated plants had approximately the same nitrogenase activity regardless of the rhizobia strain and soil type. The specific nitrogenase activity (per nodule biomass) was approximately 2 times higher than in other variants when plants were inoculated with the strain B. retamae RCAM05275 in sod-podzolic soil. In all variants of the experiment, an approximately 1.4-fold increase in the total nitrogen content and a 3-4-fold increase in nitrogen accumulation in the shoots of inoculated plants were revealed. Thus, the first data on the efficiency of inoculation with nodule bacteria of the guar cultivated in Russian soils have been obtained. Both studied strains were able to form nitrogen-fixing symbiosis, which led to a significant increase in plant biomass and accumulation of nitrogen in shoots. The results showed the promise of further research on testing strains in field experiments in order to create biopreparations to improve the nitrogen nutrition of this crop.