The efficacy of the soybean-rhizobia symbiotic systems formed by analytically selected fungicide resistant strains of Bradyrhizobium japonicum 634b, PC08 and soybean plants when the seeds were treated with fungicide Standak Top 7 days before sowing was studied in pot experiments using soil as a substrate. Standak Top inhibited the formation and functioning of symbiotic systems formed by fungicide resistant strains of B. japonicum 634b and PC08 during the first part of plant growth season (before beginning of flowering). The nodulation activity of B. japonicum 634b at flowering stage was reduced by 35 % while the fungicide and rhizobia were used for seed treatment. At the same time the nodulation activity of B. japonicum PC08 was stable. It was shown that the nitrogen fixation activity of the symbiotic systems formed by both rhizobial strains was decreased by 30—32 %. It was established that the strain B. japonicum PC08 was more effective under application of the fungicide than the strain B. japonicum 634b according to the realization of their symbiotic potential. At budding stage, the realization of symbiotic potential of the soybean-rhizobia systems formed by both strains under the effect of fungicide reached the same level as was observed in control plants (without seed treatment with fungicide). Standak Top had no toxic effect on the development of soybean plants including growth, formation of reproductive organs and grain yield while the seeds were treated with the fungicide before sowing followed by inoculation with the strains of B. japonicum 634b and PC08 on the day of sowing. The symbiotic systems of soybean formed with the analytically selected fungicide resistant strains B. japonicum 634b and PC08 had almost equal level of the realization of potential productivity with a slight advantage for the systems formed by the strain B. japonicum PC08. Soybean seed pretreatment with Standak Top did not influence significantly on plant seed productivity. The symbiotic system of soybean—B.japonicum PC08 under influence of the fungicide was more effective than the symbiotic system of soybean—B.japonicum 634b according the level of realization of symbiotic potential and productivity. Our results showed that analytically selected fungicide resistant strain B. japonicum PC08 can be used as a biological baсkground for bacterial fertilizers in order to use these fertilizers in agriculture together with Standak Top under the treatment of seeds by the fungicide 7 days before sowing.
