[Effect of aboriginal populations of soy nodule bacteria on symbiotic activity of introduced strain Bradyrhizobium japonicum 634b].

The method of limit dilutions was used to determine the number of soy nodule bacteria in soils of different regions of Ukraine. Symbiotic properties of aboriginal populations of soy rhizobia have been studied under the conditions of vegetation researches, their effect on activity of the introduced strain B. japonicum 634b has been shown. Numerous aboriginal populations of soy nodule bacteria (200-3500 units per 1 g of soil) have been found in soils of fields where soy was sown during a long period of time. It is shown that they provide for the highest degree of plants infection. These populations can compete with the standard strain. Activity of formation of symbiotic apparatus in the variants with inoculation of B. japonicum 634b remains invariable or something decreases. It has been established that populations of nodule bacteria are not numerous (20 units per 1 g of soil) or absolutely absent in the field soils where soy growing is only started. Seeds inoculation by the productive strain under conditions of these soils favours considerable increase of the number of nodules (1.3-22.0 times) and their nitrogenase activity (1.2-1.9 times).