Current Trends in the Application of Chitin and Chitosan in Agricultural Biotechnology

A comprehensive comparative evaluation was performed to assess the effectiveness of various methods for the combined application of chitin, chitosan, and strains of the genus Bacillus for plant disease protection. The application of chitin and chitosan to soil—both individually and in combination with the B. subtilis VKM B-2604D strain—demonstrated significant efficacy in reducing the incidence of Fusarium wilt in tomato and cucumber plants. The most pronounced protective effect, characterized by a 2–3-fold reduction in disease incidence, was observed when these components were applied together. Application of a B. subtilis VKM B-2604D + chitin/chitosan formulation achieved a 1.7-fold reduction in the incidence of gray rot in tomato (cv. Kupets), whereas the B. subtilis VKM B-2604D strain alone reduced it by only 1.4-fold. Introducing colloidal chitin into the nutrient medium for the large-scale submerged cultivation of B. subtilis strains significantly enhanced their antagonistic activity against Alternaria solani and Clavibacter michiganensis. A formulation comprising B. subtilis VKM B-2604D and VKM B-2605D with colloidal chitin exhibited a higher fungistatic effect against Cochliobolus sativus compared to the original strain. Foliar application of B. subtilis VKM B-2604D and VKM B-2605D + colloidal chitin formulation increased wheat resistance to dark brown spot and brown rust by 1.5–2.0 times compared to the original strains. The hydrolysis of colloidal chitin by bacterial chitinases yields chitooligosaccharides, which serve as effective elicitors of induced plant resistance. These compounds activate genes encoding protective proteins, including plant chitinase, and enhance the generation of reactive oxygen species, primarily H2O2. Hydrogen peroxide, in turn, functions as a signaling molecule, activating protein genes through redox control of transcription factors or via interaction with other signaling components. This study demonstrates that formulations based on chitin, chitosan, and selected active strains of endophytic antagonistic bacteria hold considerable promise for developing novel biopreparations with enhanced biological efficacy that strengthen plants’ natural defense responses.