Effect of different Bradyrhizobium japonicum inoculants on physiological and agronomic traits of soybean (Glycine max (L.) Merr.) associated with different expression of nodulation genes

The aim of this work was to check the effects of five Bradyrhizobium japonicum inoculants from different producers on growth, photochemical efficiency, nitrate reductase activity, amount of hydrogen peroxide, activity of catalase, non-specific peroxidase, and superoxide dismutase, seed yield, and nodulation of soybean cv. 'Malaga'. We also evaluated expression of such nodulation genes as NIC1, NOD21, and NORKb. The following inoculants were used: Nitragina IUNG, Nitragina Biofood, Nitroflora Mycoflor, Rhizobium Bio-Gen, and HiStick^® Soy. The study was carried out on plants grown in pots in an open foil tunnel or glasshouse conditions. Experimental seeds were inoculated before sowing, while the control ones were not. Physiological and biochemical analyses involved the leaves, and gene expression was investigated in the roots. The bacterial inoculants significantly affected individual parameters of chlorophyll a fluorescence. The highest photochemical efficiency was induced by Nitroflora Mycoflor, which also activated nitrate reductase to the greatest extent. Nitragina IUNG most strongly stimulated accumulation of hydrogen peroxide, facilitated formation of the greatest number of nodules, and improved seed yield per plant in comparison with the control and other inoculants. Of the studied nodulation genes, NIC1 showed the strongest expression following HiStick^®Soy treatment. Nitragina Biofood and Nitragina IUNG most significantly reduced the expression of all studied genes. Expression of NOD21 and NORKb exposed to other inoculants was the same as in the control plants. High content of hydrogen peroxide can be considered a marker of the inoculant ability to increase nodulation and yield of soybean. Commercial preparations containing the same amount of B. japonicum but different carriers of bacteria show different ability to form root nodules, and their differential impact on yield is related to the intensity of nodulation and expression of the Nod genes.