Effect of rhizobial exopolysaccharides on soybean seed germination and nodule development in the soybean-rhizobia symbiosis

The germination vigor of soybean seeds, seedlings weight, and nodulation activity during the development of soybean-rhizobia symbiosis at the vegetative stages of plant growth under the influence of the exopolysaccharides (EPS) of nodule bacteria Bradyrhizobium japonicum 634b (microsymbiont of soybean), Bradyrhizobium japonicum 631 (microsymbiont of both soybean and lupine) and Bradyrhizobium sp. ( Lupinus ) 359a, 400 (microsymbionts of lupine, with dif-ferent nitrogen-fixing activities) were evaluated in laboratory and pot experiments. It was shown that microbe EPS had no significant stimulative effect on soybean seed germination and seedling development. The tendency of increasing germination vigor and seedling dry weight was observed while the EPS400 at concentration of 0.100 mg/ml was used. This may be due to carbohydrate biopolymer properties. The decrease in the amount of the extracellular polysaccharides to 0.025 mg/ml resulted in a reduction in the soybean seedling weight but it was not reliable. Rhizobial EPS stimulated nodulation of soybean at the two trifoliate leaf stage (V2) when they were applied to seedlings before inoculation with B. japonicum 634b. There was a tendency towards an increasing the number of root nodules at the three trifoliate leaf stage (V3) and also when the soybean seedlings were incubated with EPS and then inoculated with B. japonicum 631. Early root nodule formation was observed when soybean plants were treated by the EPS634 and EPS631 and then inoculated respectively with B. japonicum 634б and B. japonicum 631. There was no clear relationship between the specificity of rhizobial polysaccharides action on seed germination, seedlings development, nodule formation in the soybean— B. japonicum symbiosis and symbiotic properties of the strains, from what the EPS were obtained. However, there was some difference between the carbohydrate biopolymers in their action.