This review examines the properties of endophytic bacteria of the genus Bacillus as objects of biocontrol and ways to expand the spectrum of their protective action based on complexes with chitosan derivatives. The mechanisms of direct and indirect effects of bacteria on the protective potential of plants are described, the role of the pro-/antioxidant system in the formation of systemic protective reactions is analyzed. The immunostimulating properties of chitosan derivatives and its modifications with organic molecules and metal nanoparticles are analyzed. The prospects of using Bacillus spp. bacterial complexes with nano- and submicron particles of chitosan derivatives to expand the spectrum of protective action of new biofungicides and immunostimulants based on them are shown.

Phytophthora infestans is, worldwide, one of the main causal agents of epiphytotics in potato plantings. Prevention strategies demand integrated pest management, including modeling of beneficial microbiomes of agroecosystems combining microorganisms and natural products. Chitooligosaccharides and their derivatives have great potential to be used by agrotechnology due to their ability to elicit plant immune reactions. The effect of combining Bacillus subtilis 26D and 11VM and conjugates of chitin with hydroxycinnamates on late blight pathogenesis was evaluated. Mechanisms for increasing the resistance of potato plants to Phytophthora infestans were associated with the activation of the antioxidant system of plants and an increase in the level of gene transcripts that encode PR proteins: basic protective protein (PR-1), thaumatin-like protein (PR-5), protease inhibitor (PR-6), and peroxidase (PR-9). The revealed activation of the expression of marker genes of systemic acquired resistance and induced systemic resistance under the influence of the combined treatment of plants with B. subtilis and conjugates of chitin with hydroxycinnamates indicates that, in this case, the development of protective reactions in potato plants to late blight proceeds synergistically, where B. subtilis primes protective genes, and chitosan composites act as a trigger for their expression.

Influence of mediators of the signal systems of salicylic (SA) and jasmonic (JA) acids and their mixture on reactive oxygen species’ (ROS) (superoxide radical and O2·− H2O2) generation and activity...

The effect of the bacteria Bacillus subtilis in combination with salicylic (SA) and jasmonic (JA) acids on the state of the pro/antioxidant system (the content of hydrogen peroxide, the activity of catalase, peroxidase, superoxide dismutase), the transcriptional activity of the genes PR-1, PR-6, and PR-9, and changes in the leaf proteome in connection with the development of potato resistance to the causative agent of late blight, the oomycete Phytophthora infestans (Mont.) de Bary, upon a moisture deficiency was studied. Plants grown from microtubers were sprayed with a suspension of B. subtilis (10⁸ cells/mL) and a mixture of bacteria with SA (10^–6 M), JA (10^–7 M), SA + JA. Three days after treatment, the plants were infected with P. infestans (10⁵ spores/mL) and cultivated under artificial soil drought conditions created with a reduction in irrigation. The biochemical parameters in plants were assessed when the soil moisture reached 40 ± 5% of full moisture capacity (7 days after infection). A decrease in the degree of P. infestans development on leaves was detected upon treatment with B. subtilis in combination with SA and JA. The mechanism of the activation of the defense systems of potato plants by bacteria of the genus Bacillus and signaling molecules under drought conditions was associated with the accumulation of H₂O₂, an increase in the activity of antioxidant enzymes, and the expression of PR-protein genes. In the proteome of potato leaves, differences were found in the presence of 19 polypeptides in the pI range from 4.0 to 9.0 with molecular weights from 30 to 125 kDa. Treatment with B. subtilis in combination with JA most significantly changed the protein spectra in both healthy and infected plants. The revealed differences in the activation of the synthesis of protective proteins under the influence of B. subtilis bacteria and signaling molecules indicate the existence of differential pathways for the formation of resistance to P. infestans in potato plants with their participation.

Viral diseases of potatoes are among the main problems causing deterioration in the quality of tubers and loss of yield. The growth and development of potato plants largely depend on soil moisture. Prevention strategies require comprehensive protection against pathogens and abiotic stresses, including modeling the beneficial microbiome of agroecosystems combining microorganisms and immunostimulants. Chitosan and its derivatives have great potential for use in agricultural engineering due to their ability to induce plant immune responses. The effect of chitosan conjugate with caffeic acid (ChCA) in combination with Bacillus subtilis 47 on the transcriptional activity of PR protein genes and changes in the proteome of potato plants during potato virus Y (PVY) infection and drought was studied. The mechanisms of increasing the resistance of potato plants to PVY and lack of moisture are associated with the activation of transcription of genes encoding PR proteins: the main protective protein (PR-1), chitinase (PR-3), thaumatin-like protein (PR-5), protease inhibitor (PR-6), peroxidase (PR-9), and ribonuclease (PR-10), as well as qualitative and quantitative changes in the plant proteome. The revealed activation of the expression of marker genes of systemic acquired resistance and induced systemic resistance under the influence of combined treatment with B. subtilis and chitosan conjugate indicate that, in potato plants, the formation of resistance to viral infection in drought conditions proceeds synergistically. By two-dimensional electrophoresis of S. tuberosum leaf proteins followed by MALDI-TOF analysis, 10 proteins were identified, the content and composition of which differed depending on the experiment variant. In infected plants treated with ChCA, the synthesis of proteinaceous RNase P 1 and oxygen-evolving enhancer protein 2 was enhanced in conditions of normal humidity, and 20 kDa chaperonin and TMV resistance protein N-like was enhanced in conditions of lack of moisture. The virus coat proteins were detected, which intensively accumulated in the leaves of plants infected with potato Y-virus. ChCA treatment reduced the content of these proteins in the leaves, and in plants treated with ChCA in combination with Bacillus subtilis, viral proteins were not detected at all, both in conditions of normal humidity and lack of moisture, which suggests the promising use of chitosan derivatives in combination with B. subtilis bacteria in the regulation of plant resistance.