Biological background to using chitosan inducers to increase the efficiency of biofungicides

Microbiological preparations form the basis of modern technologies phytosanitary optimization of agroecosystems, therefore, increasing their efficiency in protecting crops from a wide range of plant pathogens is an urgent task of crop production. The All-Russian Research Institute of Plant Protection (VIZR) has developed Vitaplan, a biological product based on the composition of two strains, the Bacillu subtilis VKM B-2604D and B. subtilis VKM B-2605D with a different composition of active complexes and a mechanism of action that are highly effective against a wide range of plant pathogens. The aim of the study is to substantiate increasing the biological effectiveness of new Vitaplan formulations supplemented with chitosan as an inducers of plant resistance. In this work, for the first time, two new formulations were developed, the Vitaplan, CF + colloidal chitin and the Vitaplan, CF + 0.1 % chitosan salicylate with increased antagonistic and elicitor activity compared to the original biological Vitaplan, CF. The effect of disease resistance inducers, such as colloidal chitin and chitosan salicylate, on the biological activity of Vitaplan has been investigated. The colloidal chitin (1 %) added to the deep culture medium increased the antagonistic activity of B. subtilis VKM B-2604D and VKM B-2605D against the tomato bacterium Clavibacter michiganensis subsp. Michiganensis (Smith) Davis et al. (strain 101) and the fungus Alternaria solani Sorauer, and also ensured effective suppression of the growth of Cochliobolus sativus mycelium up to 84.9-88.1 % on day 5 and day 7 of the experiment, which is comparable to the efficiency of Vitaplan CF (80.9-87.5 %, respectively). Chitosan salicylate at a concentration of 0.1 % had a moderate fungistatic activity, with only 36.5-46.0 % suppression of the growth of the C. sativus mycelium. The study of the immunomodulatory activity of various Vitaplan CF preparative forms in protecting wheat against the brown spot pathogen Cochliobolus sativus (S. Ito & Kurib.) was carried out under various infectious loads. Depending on the infectious load of the pathogen, preliminary spraying of wheat plants with Vitaplan, CF at a dilution of 1:10 followed by infection with the brown spot pathogen reduced the leaf lesion area to 50-80 % compared to 65-100 % in control. Adding 1.0 % colloidal chitin to the culture medium for the producer strains reduced leaf damage to 40-50 %, which indicates a higher immunomodulatory activity of this form of Vitaplan compared to Vitaplan CF at a dilution of 1:10. Chitosan salicylate proved to be an effective inducer of disease resistance, reducing damage to wheat plants by dark brown spots to 10-20 %, depending on the infectious load. The addition of chitosan salicylate at a concentration of 0.1 % to original form Vitaplan, CF at a 1:10 dilution also had a positive effect on the antagonist with a 2.0-2.5-fold increase of its biological activity. The biological effectiveness of the new formulation Vitaplan CF (1:10) + chitosan salicylate (0.1 %) in protecting wheat from brown spot when spraying plants is determined by two mechanisms, i.e., by i) direct pathogen suppression due to antibiotics and enzymes the B. subtilis VKM B-2604D and B. subtilis VKM B-2605D produce, and ii) through the induction of plant systemic resistance. The chitosan salicylate in the Vitaplan biological increases the inducing activity of this new formulation compared to the original form. Thus, the prospect of combining active selected strains of microbial antagonists of plant pathogens and chitosan complexes to increase the biological efficiency and expand the spectrum of action of drugs has been experimentally confirmed and theoretically substantiated.