Symbiotic Nitrogen Fixation, Phosphorus and Potassium Uptake Capacity of a Number of Soybean Mutant Lines in a Calcareous Soil

The objectives of the present study was to evaluate biological nitrogen fixation, P and K uptake ability of ۳۱ soybean mutant lines (induced by Gamma irradiation) and their parent cultivar at greenhouse level. Initially, ۱۰ Rhizobial isolates and strains were tested for infectiveness and symbiotic effectiveness using Leonard jars, and the strain Bradyrhizobium japonicum strain RS ۱۵۲ was selected as the most efficient strain. The experiment was conducted under proper greenhouse condition with a randomized complete block design on a soil with no indigenous rhizobia and low nitrogen and phosphorus content. Thirty-one soybean mutant lines and two inoculated and un-inoculated wild cultivar blanks were replicated three times. Each pot contained ۳.۵ kg air-dried homogenized soil, and at the time of planting each seedling was inoculated with l mL of inoculum RS ۱۵۲ containing approximately ۹ × ۱۰۸ cells per mL. During about ۴ months of growth, the plants were irrigated to maintain the soil moisture approximately ۰.۸ field capacity. The plants were harvested at the plant developmental stage of pod filling (R۶), and several parameters, such as dry matter of shoot, nodule and roots, number of nodules, and proportion and amount of Nitrogen derived from air (Ndfa% and N-fixed) were measured. According to the results, in most parameters, the mutant lines were significantly different with each other and also with the L۱۷ parent soybean cultivar. The mutant line ۵ showed the maximum value of %Ndfa (۷۳.۰۶۸) compared to the cultivar L۱۷ (۴۸.۷۶۲), indicating significant increase of biological nitrogen fixation, by about fifty percent, through physical mutagenesis. In addition, the mutant lines ۲۱ and ۳۱ had higher phosphorus and potassium uptake than the others, however, significant differences were observed for phosphorus uptake capacity compared to the cultivar L۱۷. Although more detailed studies are needed to evaluate effects of these mutations on nitrogen fixation, macro- and microelements absorption capacity, and also on yield and quality parameters, these findings show that gamma irradiation could be helpful to induce new nutritional properties in soybean and release new mutant cultivars.