Aim. The elaboration of efficient legume-rhizobial symbiosis systems, involving active strains of nodule bacteria, in the
combination with fungicide seed treatment may be an alternative method of providing ecologically friendly nitrogen sources
to plants and promoting their tolerance to the external factors, which is relevant for preservation and restoration of envi-
ronmental quality. Therefore, the aim of our study was to determine the impact of pre-sowing seed treatment with fungi-
cides, which differ in the action spectrum of active substances – Standak Top (fipronil, 250 g/l, thiophanate-methyl, 225 g/l,
pyraclostrobin, 25 g/l) and Maxim XL (fludioxonyl, 25 g/l, metalaxyl, 10 g/l), on the intensity of the development of lipid
peroxidation processes, the activity of antioxidant enzyme ascorbate peroxidase and nitrogen fixation activity in soybeans on
the early stages of forming legume-rhizobial symbiosis. Methods. Microbiological (cultivation of a bacterial culture, seed
inoculation), physiological (vegetative experiment), biochemical (spectrophotometric determination of the content of lipid
peroxidation products and the activity of ascorbate peroxidase; measuring the nitrogen-fixation activity using a gas chro-
matography). Results. It was found that pre-sowing fungicide treatment of soybean seeds and subsequent inoculation with
active rhizobia of strain 634b did not result in the change in the content of TBA-active products in roots and root nodules (the
values of indices were within the experiment deviation). At the same time, after seed inoculation using rhizobia and treat-
ment with Maxim XL, there was an increase in the activity of ascorbate peroxidase in the roots from 20.3 to 30.8 %, and with
Standak Top – from 20.0 to 29.8 % during the early stages of ontogenesis till the formation of the third ternate leaf. Here,
the activity of the enzyme in root nodules increased by 24.7–40.3 % at the fungicidal effect. Our data demonstrate that the
combination of fungicide seed treatment and inoculation with active rhizobia does not induce lipid peroxidation processes,
but promotes the initiation of protective antioxidant properties in soybeans. It is accompanied with efficient functioning of
the symbiotic apparatus, which is manifested in the increase in nitrogen-fixing activity of nodule bacteria, formed by active
rhizobia of strain 634b after the seed treatment with Standak Top – by 98.3 and 78.1 % and after Maxim XL – by 78.6 and
196.2 % respectively, during the stages of the second and third ternate leaves. Conclusions. The pre-sowing soybean seed
treatment with fungicides Standak Top and Maxim XL and the subsequent inoculation with active rhizobia of strain 634b
does not induce the development of lipid peroxidation processes, but increases the activity of the antioxidant enzyme, ascor-
bate peroxidase, in the roots and root nodules, which is accompanied with the efficient work of the symbiotic apparatus on
the early stages of determining legume-rhizobial symbiosis. This method of seed treatment may be a novel measure, to use
in the technologies of cultivating soybeans to enhance the realization of the symbiotic potential and meet the needs of plants
in ecologically friendly nitrogen, and to promote the formation of their tolerance to the corresponding cultivation conditions.
The prospect of using the cyanobacterium Nostoc muscorum to improve vital activity of barley seedlings by various methods of seed treatment
