Physiological and Biochemical Changes in Soybean Plants Caused by Iodine-Selenium Chelates and Phytopathogenic Bacteria

The search for effective and environmentally sound measures to fight against plant diseases caused by phytopathogenic microorganisms is of great importance. It is especially important to investigate alternative measures to protect cultivated plants that combine elements beneficial to human health such as iodine and selenium. Purpose. The study of physiological and biochemical changes in soybean leaves after artificial inoculation of plants with different strains of phytopathogenic bacteria on the background of pre-sowing treatment of seeds with a solution of iodine-selenium (I-Se) chelates. Methods. Soybean plants of the Artemis variety were grown in field conditions. Before sowing, the seeds were treated with a 1% I-Se chelated solution (I — 80 mg/L and Se citrate — 0.05 mg/L). The experimental plants were inoculated with phytopathogenic bacteria from the microbiological collection of the Zabolotny Institute of Microbiology and Virology of the National Academy of Sciences, namely Pseudomonas savastanoi pv. glycinea IMВ B-9190, P. agglomerans IMВ B-9185, and P. syringae pv. syringae IMВ B-8531. The contents of chlorophyll-a, b and carotenoids in the leaves were determined by extraction in DMSO followed by spectrophotometry. Catalase activity was determined by the method of titrimetric permanganatometry with a 0.01M solution of KMnO4, the activity to non-specific peroxidases — according to Boyarkin’s method. Evaluation of the photochemical activity of photosynthesis according to the parameters F0, Fv/Fm, and RFd was carried out by the method of induction of chlorophyll fluorescence using a portable device «Floratest». Statistical processing of experimental data was carried out using the built-in functions of the Microsoft Excel program. Results. The increase of peroxidase activity of leaves was revealed after both pre-sowing treatment with 1% I-Se solution of intact plants and inoculation of them with different strains of bacterial pathogens in the following order: I-Se > I-Se+P. syringae pv. syringae 8531 > I-Se+P. agglomerans 9185 > I-Se+P. savastanoi pv. glycinea 9190. The catalase activity of leaves tissues increased only when infected with a specific pathogen P. savastanoi pv. glycinea 9190 (by 20.6%). After artificial inoculation with strains of both specific and facultative bacterial pathogens and the pre-sowing treatment with I-Se, there was observed an increase in the quantum efficiency of PSII (Fv /Fm) and fluorescence in decline index (Rfd). An increase in the content of chlorophyll-a (by 18%), b and carotenoids (by 7%) in the leaves after the pre-sowing treatment with I-Se has been shown. The content of chlorophyll-a in soybean leaves due to pre-sowing treatment with I-Se had the most significant increase after inoculation of P. agglomerans 9185 (20%). Due to the inoculation with a specific pathogen P. savastanoi pv. glycinea 9190 (after the pre-sowing treatment with I-Se), the content of chlorophyll-a tended to decrease, and the content of chlorophyll-b decreased by 7%. The carotenoid content in leaves increased significantly at inoculation of plant with facultative pathogens: P. agglomerans 9185 (by 28.2%) and P. savastanoi pv. syringae 8531 (by 20.7%). The chlorophyll a/b ratio increased in all experimental variants. Conclusions. 1. It was found that pre-sowing seed treatment with 1% I-Se chelated solution results in increasing disease resistance in nonspecific adult soybean plants, including increasing their thermotolerance. This is evidenced by increasing the peroxidase activity of leaves and the content of photosynthetic pigments in natural conditions: chlorophyll-a and carotenoids. 2. Inoculation of soybean plants with a specific pathogen causes an increase in catalase and peroxidase activities in leaves. The significant increase in peroxidase activity after plant inoculation with facultative pathogens was shown. 3. A significant increase in the content of chlorophyll-a in soybean leaves after inoculation with P. agglomerans 9185 and pre-sowing treatment with I-Se was observed. The significant reduction of chlorophyll-b in leaves due to the inoculation of plants with P. savastanoi pv. glycinea 9190 and pre-sowing treatment of the seeds with I-Se was shown. The most significant increase in the content of carotenoids in leaves was detected after inoculation of plants with facultative pathogens — P. agglomerans 9185 and P. syringae pv. syringae 8531. 4. Significant stimulation of both maximum quantum yield of PSII photochemistry (Fv /Fm) and the rate of carbon assimilation (Rfd) due to the pre-sowing seed treatment with I-Se and inoculation of plants with different strains of phytopathogens was observed. It resulted from the activation of antioxidant systems and increased need for assimilates due to changes in plant metabolism.