Forming Soybean Productivity Upon Seed Pre-Treatment With Fungicides Standak Top and Fever and Inoculation With Rhizobia on the Day of Sowing

Abstract

Soybean grain productivity is largely due to a complex of factors, in particular, the efficiency of symbiotic systems formed with nodule bacteria, the activity of growth processes and the formation of vegetative and generative organs by plants, as well as their adaptive plasticity under various environmental factors. The article presents the results of studying the peculiarities of the formation of soybean plant productivity upon seed pre-treatment with fungicides of different classes and inoculation with nodule bacteria on the day of sowing. Objective. To study the dynamics of seed germination, formation of vegetative and generative organs and soybean harvest, functioning of soybean-rhizobial symbiosis, as well as the state of photosynthetic pigment system — content of chlorophyll a and b and carotenoids in the leaves upon seed pre-treatment with fungicides Fever and Standak Top and bacterization with Bradyrhizobium japonicum 634b on the day of sowing. Methods. Microbiological, physiological, biochemical, statistical. Results. Fungicides did not exert toxicity in terms of seed germination, and soybean seed germination under the action of Fever exceeded parameters in the control plants by 20 % (at Day 5 after sowing) and by 7 % (at Day 8). It has been shown that fungicides increased plant height, aboveground mass and accelerated the formation of generative organs (flowers) by plants but did not significantly affect root mass. It was found that fungicides had a pronounced toxic (inhibitory) effect on soybean-rhizobial symbiosis upon seed pre-treatment: the process of nodule formation was suppressed in the initial stages of symbiosis, nitrogen fixation activity was lower than in the control plants by 80–48 % depending on soybean development phase. Thus, the effect of fungicides Fever and Standak Top upon seed pretreatment and inoculation with nodule bacteria on the day of sowing was characterized by significant suppression of functional activity of the symbiotic apparatus in the first half of soybean vegetation and its gradual recovery during formation of generative organs. Although fungicides inhibit the formation and functioning of legume-rhizobial symbiosis but their positive effect on the plant itself (seed germination, plant height, aboveground mass accumulation, dynamics of generative organ formation), as well as the ability of plants to adapt to stress at the biochemical level (stabilization of the content of photosynthetic pigments in the leaves) allowed to form a crop of soybean seeds at or slightly above the level of control. Conclusion. Physiological and biochemical features of the reaction of soybean-rhizobial symbiosis to the action of different fungicides that we had established must be taken into account in developing new strategies to protect plants from pathogens of various aetiologies with the involvement of physiologically active substances having fungicidal activity in combination with inoculation.