Infections of agricultural crops caused by pathogen ic fungi are among the most widespread and harmful, as they not only reduce the quantity of the harvest but also significantly deteriorate its quality. This study aims to develop unique seed-coating formulations incorporating biopolymers (polyhydroxyalkanoate and pullulan) and beneficial microorganisms for plant protection against phytopathogens. A microbial association of biocompatible endophytic bacteria has been created, including Pseudomonas flavescens D5, Bacillus aerophilus A2, Serratia proteamaculans B5, and Pseudomonas putida D7. These strains exhibited agronomically valuable properties: synthesis of the phytohormone IAA (from 45.2 to 69.2 µg mL⁻¹), antagonistic activity against Fusarium oxysporum and Fusarium solani (growth inhibition zones from 1.8 to 3.0 cm), halotolerance (5–15% NaCl), and PHA production (2.77–4.54 g L⁻¹). A pullulan synthesized by Aureobasidium pullulans C7 showed a low viscosity rate (from 395 Pa·s to 598 Pa·s) depending on the concentration of polysaccharide solutions. Therefore, at 8.0%, w/v concentration, viscosity virtually remained unchanged with increasing shear rate, indicating that it exhibits Newtonian flow behavior. The effectiveness of various antifungal seed coating formulations has been demonstrated to enhance the tolerance of barley plants to phytopathogens.

In this study, 382 isolates of bacterial endophytes from tissues of plants grown in the foothills and piedmont plains of the Trans-Ili Alatau were isolated. It was found that certain strains actively produce indole-3-acetic acid (IAA) in a medium containing l-tryptophan. Among the strains studied, 26 strains (66%) showed a positive response to production of IAA. Bacteria synthesized IAA in the range of 18.6 ± 1.1 to 82.4 ± 2.3 µg/ml. IAA was synthesized more actively by Streptosporangium sp. KK1 (44.1 µg/ml), Rhodococcus sp. KK 2 (42.5 µg/ml), Streptomyces tendae KK3 (44.9 µg/ml) strains. The most active auxin's producer is a Jeotgalicoccus halotolerans BAK1 strain, whose total level of IAA production reached 82.4 µg/ml. Such strains as Streptomyces griseorubiginosis KK4, Streptomyces sp. KK5 and Jeotgalicoccus halotolerans BAK1 were found to have a significant stimulating effect which was reflected in the increase of the length of the roots of soybean and barley. As a result, 8 promising strains with fungicidal, growth-stimulating, phosphorus dissolving and enzymatic activities were selected for the further development of highly microbiological preparations for crop research.

Due to the increasing use and accumulation of petrochemical plastics in the environment and the rapid depletion of natural resources, microbial polyhydroxyalkanoates have great potential to replace them. This study provides new insights in the field of obtaining of polyhydroxyalkanoates (PHAs) from endophytic bacterial strains and applying them as potential biocontrol agents against postharvest diseases of apples. Two strains—Pseudomonas flavescens D5 and Bacillus aerophilus A2—accumulated PHAs in amounts ranging from 2.77 to 5.9 g L⁻¹. The potential to use low-cost substrates such as beet molasses and soapstock for PHA accumulation was shown. The PHAs produced by the Ps. flavescens D5 strain had pronounced antagonistic activity against Penicillium expansum (antifungal property = 62.98–73.08%). The use of PHAs as biocontrol agents significantly reduced the severity of apple blue mold, especially in the preventive treatment option.

Among the different strategies of plant protection from phytopathogens, the use of beneficial fungi has been described as a sustainable, eco-friendly approach. The aim of the present work was to evaluate the antagonistic activity of beneficial fungal strains in vitro and in vivo. The studied strains (Beauveria bassiana T7, Beauveria bassiana T15, Metarhizium robertsii An1, Talaromyces pinophilus T14) had pronounced antagonistic activity against three phytopathogens (the growth inhibition was 18.2–51%). In pot experiments, the studied strains significantly reduced the level of stress in barley plants caused by phytopathogenic load. The beneficial effect of the strains consisted of an increase in the morphometric parameters of plants and a positive effect on photosynthetic pigments and proline levels. The 1-aminocyclopropane-1-carboxylate deaminase level of the strains varied from 0.95 to 2.73 µM α-KB mg protein⁻¹ h⁻¹. The most significant mechanisms of antagonistic action of the M. robertsii An1 strain were the following: the production of hydrolytic enzymes (chitinase and glucanase activity amounted to 0.23 U mL⁻¹ and 3.42 U mL⁻¹, respectively) and the synthesis of soluble volatile and non-volatile compounds with antifungal properties, including destruxin E, destruxin A, and hydroxyanthraquinones. The results obtained revealed the potential of the studied strains for their integration into a sustainable agricultural system.