Effect of microorganisms with fungicidal and insecticidal actions on biological activity of soil of root zone of maize

Abstract

Intensive agricultural production and high crop yields increase the anthropogenic load not only on agrocenoses, but also natural ecosystems. Obtaining the highest quality agricultural products with high yields is the foundation of efficient management. However, one of the obstacles to obtaining such products are diseases of crops, the pathogens of which are transmitted through seed or accumulate in the soil. Pre-sowing treatment of seeds with pesticides of protective and insecticidal action has a significant advantage over the treatment of vegetative plants, as it is less time-consuming and economically feasible.

Farmers, in today's conditions, to combat pests and plant diseases, fungal and bacterial origin, are offered a wide range of chemical seed disinfectants. The vast majority of modern chemical pesticides eliminate existing problems, but lead to the deterioration of the ecological state of agrocenoses. Therefore, the biological method of protection based on the use of living microorganisms and products of their metabolism is becoming more and more widespread in agricultural technologies during the cultivation of cereals.

The aim of our work was to determine the effect of the composition of promising strains of microorganisms that have protective and insecticidal effects on the biological activity of the soil of the root zone of maize plants.

Maize hybrids Khorol SV (FAO 270) and Vizier (FAO 350) were used in the study. The area of the experimental plots is 25.2 m2 with a row spacing of 0.7 m and a seed sowing rate of 50 thousand seeds per ha. Repeatability of the experiment - 3 times. Agricultural techniques are generally accepted for the conditions of the Forest-Steppe. Pre-sowing treatment of maize seeds was performed with a mixture of chemicals (Maxim XL and Cruiser, Syngenta) and a complex of microorganisms № 1 (Paenibacillus polymyxa 6M, Pseudomonas fluorescens K-11, titer ‒ 3.2 * 109 CFU / ml, use rate ‒ 0, 5 l per 100 kg of seeds) and № 2 (Bacillus thuringiensis 2729 and Streptomyces spp., titer ‒ 4.7 * 109 CFU / ml, utilization rate 1.25 l per 100 kg of seeds). Research scheme: 1. control (corn seeds without treatment), 2. pre-sowing treatment of seeds with a mixture of drugs Maxim XL+Cruiser; 3. pre-sowing treatment of seeds with a complex of compositions of microorganisms № 1 and № 2.

Soil samples were taken in the phase of ejection of the panicle in accordance with generally accepted methods. Determined: the number of micromycetes, the carbon content of microbial biomass, the intensity of carbon dioxide emissions from the soil, phytoxicity and antifungal activity. Statistical processing of experimental results was performed in the program Statistica 6.0.

The root zone of plants has the highest activity where all the positive and negative aspects of the relationship between microorganisms and plants are manifested. And the quantitative characteristic of these relationships is the biological activity of the soil.

It is shown that pre-sowing treatment of maize seeds Maxim XL+Cruiser inhibited the development of micromycetes in the soil by 2.4–3.3 times compared to the control. However, the use of a complex of compositions № 1 and № 2, in terms of efficiency was not inferior to chemicals and contributed to a reduction in the number of micromycetes by 1.8–2.2 times. Thus, the protective function of the complex of compositions of microorganisms № 1 and № 2 was manifested in inhibiting the development of microscopic fungi during the growing season of maize plants, which in turn indicates the successful colonization of the root zone of maize plants by microorganisms-agents of compositions № 1 and № 2. It was found that the biomass content of microorganisms depended on the means of pre-sowing seed treatment, type of hybrid and year of study. It should be noted that seed treatment Maxim XL + Cruiser reduced the microbial biomass by 27-32.5% depending on the maize hybrid. It was found that the use of a complex of compositions of microorganisms № 1 and № 2 contributed to an increase in carbon dioxide emissions by 5.4‒10.8% compared to the control and variants with chemical seed treatment. In turn, the emission index of soil carbon dioxide decreased under the action of chemicals by 13–18.8% relative to the control, which indicates a decrease in the intensity of microbiocenosis of the root zone of maize plants. It should be noted that the soil of the root zone of maize plants in the phase of panicle ejection did not have phytotoxic properties, which proves the lack of accumulation of spores of phytopathogenic fungi and bacteria in the soil. The antifungal activity of the soil of the maize root zone was determined by the inhibition of the development of the test culture and the zone of mycelial lysis around the soil lumps. In the control variant, where no seed treatment was performed, the transparent zones of growth inhibition of the phytopathogen ranged from 1.1 to 2.3 mm. Therefore, according to the scale of antifungal activity, the control variant is characterized by a low level. The use of a complex of compositions of microorganisms № 1 and № 2 contributed to the increase of antifungal activity of the soil, the zone of suppression of the test culture was 8.1 - 9 mm (which is 4-7.3 times higher than the control variant, and 1.5 times higher than the use of chemical drugs). Thus, in the conditions of temporary field studies it is proved that bioagents of the complex of compositions of microorganisms № 1 and № 2, introducing into the root zone of maize plants by pre-sowing seed treatment initiate changes in the soil microbiocenosis. Therefore, the complex of compositions of microorganisms № 1 and № 2 is a promising basis for the creation of a complex biological product with fungi-insecticidal properties. The complex of compositions of microorganisms № 1 and № 2 is recommended for agricultural producers as one of the modern methods of ecologically safe agriculture, which will provide biological control of plant diseases during the whole period of their growth, as well as during storage of agricultural products and seeds.