INFLUENCE OF MIXED CULTURES OF LUPIN AND FODDER GALEGA RHIZOBIA ON NODULATION, NITROGEN FIXATION, GROWTH AND YIELD COMPONENTS OF LUPIN

Objective. Evaluate root nodule formation, nitrogen fixation rates and lupine growth under seed inoculation with the microbial compositions of lupine and fodder galega nodule bacteria as well as to estimate lupine yield components. Methods. Yellow lupine (Lupinus luteus L.) cv. Kruglyk was grown in small-scale field experiments. Lupine seeds were inoculated with Bradyrhizobium lupini strain 359a (rhizobia nodulating lupine) mixed with Neorhizobium galegae strains 0702, 0703, or MC-1 (rhizobia nodulating fodder galega). The number and weight of nodules as well as shoot weight at both the six-leaf (BH31) and budding (BH51) stages were determined. The number and weight of seeds per plant and 1000-seed weight were also examined. The rate of nitrogen fixation was measured by acetylene reduction assay. Results. The binary consortia of lupine and fodder galega nodule bacteria differed from each other in their effects on the establishment of the symbiosis of lupine with B. lupini and on the aboveground growth of plants. The extent of effects of the consortia depended on their composition. The combined inoculation with B. lupini 359a and N. galegae 0702 led to an increase in the number and weight of root nodules at the six-leaf growth stage as compared to control (inoculation with 359a only). At the same time the mentioned mixed culture promoted the aboveground growth of lupine during the period of experiments. The application of B. lupini strain 359a in combination with N. galegae strain MC-1 resulted in an increase in the number of root nodules and low nitrogen fixation rates. But besides that, an insignificant stimulating effect on lupine shoot weight was observed for a binary consortium consisting of 359a and MC-1. There were no differences in efficacy between a single-strain (B. lupini 359a) and a two-strain (B. lupini 359a + N. galegae 0703) inoculation of plants. The tested mixed cultures of nodule bacteria did not significantly influence nodule weight, nitrogen fixation rates at the budding stage, seed number and seed weight. Conclusion. The results indicate that the binary consortia of lupine and fodder galega nodule bacteria possess the potential to affect symbiotic parameters and lupine growth at the early growth stages. Additionally, it is shown that the composition of microorganisms in mixed cultures plays an important role in determining their efficiency. The combined inoculation with B. lupini strain 359a and N. galegae strain 0702 shows the prospect for its application on lupine cultivation but additional studies of the effects of this microbial consortium involving a broad range of plant cultivars as well as different soil types are needed.