Optimization of the search for highly efficient nodule bacteria strains for inoculation of legume plants

Highly effective strains of nodule bacteria are the main component of microfertilizers used in the cultivation of leguminous plants. Using artificial inoculation with rhizobia, it is possible to achieve a significant increase in the yield of this crop. The most common way to search for highly effective strains of these microorganisms is to obtain them from the nodules of the plants themselves with subsequent selection of strains that most effectively affect plant yield. In this work, we analyzed bacteria obtained from nodules collected at different stages of development of such leguminous plants as Trifolium hybridum L., Lotus corniculatus L., and Galega orientalis Lam . It is shown that each plant enters into symbiosis with only one specific type of bacteria, but with a large number of its genetic variants, each of which can potentially have individual symbiotic characteristics. The greatest variety of strains was found in the nodules of Trifolium hybridum , and the microsymbionts of Galega orientalis were characterized by uniformity. It was found that at the beginning of the development of all three plant species, the nodules are formed by the most diverse strains of rhizobia which have high nitrogen-fixing activity ranging from 3.17 to 32.70 N2·plant-1·h-1 for microsymbionts of the L. corniculatus , from 10.08 to 30.75 N2·plant-1·h-1 for microsymbionts of G. orientalis , from 9.91 to 32.42 N2·plant-1·h-1 for microsymbionts of T. hybridum . Among them, highly effective strains are found more often than in other periods. In the middle of the growing season, bacteria that form nodules on the roots of the studied leguminous plants have relatively leveled values of nitrogen fixation efficiency, from 6.35 to 19.13 N2˛plant-1˛h-1 for microsymbionts of the L. corniculatus , from 15.51 to 23.47 N2·plant-1·h-1 for microsymbionts G. orientalis , from 11.61 to 20.53 N2·plant-1·h-1 for microsymbionts of T. hybridum , and their activity of nitrogen fixation are lower compared to maximum activity found in strains from nodules at the beginning of the growing season. At the end of the life cycle, nodules on the roots of the analyzed plants are formed by microorganisms that fix nitrogen with different efficiency but are still inferior in this trait to the most active «spring» strains. Thus, we believe that the search for effective strains of nodule bacteria is most productive at the initial stage of plant development.