Influence of fungicides on activities of enzymes of phenolic metabolism in the early stages of formation and functioning of soybean symbiotic apparatus

We studied the effect of complex seed treatment with fungicides and rhizobium culture on the activity of phenolic metabolism enzymes – polyphenol oxidase and guaiacol peroxidase in the early stages of the formation and functioning of various symbiotic systems Glycine max – Bradyrhizobium japonicum. In the research we used microbiological, physiological, biochemical methods, gas chromatography and spectrophotometry. The objects of the study were selected symbiotic systems formed with the participation of soybean (Glycine max (L.) Merr.), Diamond variety, strains Bradyrhizobium japonicum 634b (active, virulent) and 604k (inactive, highly virulent) and fungicides Maxim XL 035 PS (fludioxonil, 25 g/L, metalaxyl, 10 g/L), and Standak Top (fipronil, 250 g/L, thiophanate methyl, 225 g/L, piraclostrobin, 25 g/L). Before sowing, the seeds of soybean were treated with solutions of fungicides, calculated on the basis of one rate of expenditure of the active substance of each preparation indicated by the producer per ton of seed. One part of the seeds treated with fungicides was inoculated with rhizobium culture for 1 h (the titre of bacteria was 108 cells in 1 ml). The other part of the fungicide-treated seeds was not inoculated by rhizobium culture. As a result of the research, it was revealed that an effective symbiotic system formed with the participation of soybean plants and the active strain rhizobia 634b is characterized by a high level of polyphenol oxidase activity and low guaiacol peroxidase in roots and root nodules in the stages of second and third true leaves. Such changes in the activity of enzymes occurred along with the formation of nodules which actively fixed the molecular nitrogen of the atmosphere. An ineffective symbiotic system (strain 604k) is characterized by an elevated level of polyphenol oxidase activity in the roots and guaiacol peroxidase in the root nodules, which is accompanied by activation of the process of nodulation. Treatment of soybean seeds with fungicides in an effective symbiotic system leads to a change in the activity of the enzymes of the phenolic metabolism, which induced adaptive changes in plant metabolism and growth of nitrogenase activity of the root nodules. The recorded changes in the activity of both enzymes for the action of fungicides in the ineffective symbiotic system can be considered as a kind of response of the plant to the treatment and were observed along with the reduction of the processes of nodulation into the stage of the third true leaf.