Role of nitrogen deficiency on growth and development near isogenic by E genes lines of soybean co-inoculated with nitrogen-fixing bacteria

Abstract

Nitrogen deficiency is a limiting factor in increasing efficiency of crop production in terrestrial ecosystems, and the transformation of inert nitrogen to forms that can be assimilated by plants is mediated by soil microorganisms. Symbiotic nitrogen-fixing bacteria and roots depend on each other and have developed various mechanisms for symbiotic coexistence. The aim of this work was to investigate the role of nitrogen deficiency on growth and development near isogenic by E genes lines of soybean (Glycine max (L.) Merr.): short-day (SD) line with genotype Е1е2е3(Е4е5Е7), and photoperiodic insensitive (PPI) line with genotype е1е2е3(Е4е5Е7) grown from seeds inoculated with active strains of Bradyrhizobium japonicum against the background of local populations of diazotrophs of the genus Azotobacter spp. and establish how the soybean – Bradyrhizobium symbiosis will develop as the genes of both microsymbionts and macrosymbionts are responsible for the formation of the symbiotic complex. Plants were grown in a vegetation chamber, in sand culture. To assess the quantitative composition of microorganisms in the rhizosphere and rhizoplanes, 6 plants were selected from each soybean line, then separation of the zones of the rhizosphere and rhizoplanes was performed using the method of washing and the resulting suspension was used for inoculation on dense nutrient media (mannitol-yeast agar medium and Ashby medium). The results of study showed that seed inoculation and co-inoculation provides faster formation of the symbiotic soybean – Bradyrhizobium complex. Differences in nodulation rates between the short-day line with genotype Е1е2е3(Е4е5Е7), and a photoperiodic insensitive line with genotype е1е2е3(Е4е5Е7) were identified. Determination of the amount of B. japonicum on the medium of mannitol-yeast agar in the rhizosphere and rhizoplane showed that inoculation by B. japonicum strain 634b caused a significant increase in the amount B. japonicum in the rhizosphere and rhizoplane in both soybean lines, comparison with non-inoculated seeds. Then, co-inoculation by B. japonicum strain 634b + Azotobacter chroococcum significantly increased the amount of B. japonicum only in the rhizoplane and decreased their number in the rhizosphere. Determination of the amount of A. chroococcum on the Ashby elective medium in the rhizosphere and rhizoplane showed that the inoculation by B. japonicum strain 634b caused a significant decrease in the amount of A. chroococcum both in the rhizosphere and in the rhizoplane of the PPI line of soybean, and in the rhizosphere the SD line, in comparison with non-inoculated seeds. That can testify to the competitive interaction of these microorganisms. However, the co-inoculation by B. japonicum strain 634b + A. chroococcum in the SD line significantly increased the number of A. chroococcum in the rhizoplane and decreased their number in the rhizosphere, in the PPI line their number decreased in the rhizoplane and increased in the rhizosphere, in comparison with non-inoculated seeds. Probably, the E genes (their dominant or recessive state) of soybean isogenic lines affect the regulation of the content and distribution of sugars. It was established that the nitrogen deficiency stimulated development of the root system of plants and the synthesized sugars were distributed predominantly to the root system growth. We suppose that the seeds’ inoculation had extended sugar consumption to the symbiont, due to which it compensates the lack of nitrogen, but leads to a slower growth of the root system.

Keywords

• bradyrhizobium japonicum; azotobacter chroococcum; glycine max; isogenic lines; symbiosis; photoperiodic insensitive lines.