Effect of chitosan salicylate on the antagonistic activity of <i>Bacillus subtilis</i> against the dark brown spot <i>Bipolaris sorokiniana</i>

The aim of the study was to develop a method for enhancing the antagonistic activity of B. subtilis strains by including chitosan salicylate (CS) in the nutrient medium during submerged cultivation to improve the efficiency of multifunctional biopreparations based on them. In this regard, the effect of different concentrations of CS (0.05 %; 0.1 %; 0.2 %; 0.5 %) on the growth, development and antagonistic activity of the studied strains was assessed. High antagonistic activity of the studied B. subtilis strains against the causative agent of dark brown spot Bipolaris sorokiniana was shown, which provided a fungal growth inhibition zone with a diameter of 41 mm and effective suppression of conidia germination – up to 52.0 % compared to the control (87.1 %). The optimal concentration of CS (0.05 and 0.1 %) for inclusion in the medium was experimentally established, increasing the initial level of antagonistic activity by ~ 20 %, which was confirmed by an increase in the fungal growth inhibition zone from 41 mm to 45…47 mm while maintaining the efficiency of inhibiting ascomycete conidia (50.0 % and 45.0 %), respectively. Increasing the CS concentration in the nutrient medium to 0.2 % and 0.5 % led to a more than 2-fold decrease in the diameter of the fungal growth inhibition zone, which was 17.5…17.7 mm. In addition, in these experimental variants, the B. subtilis strains practically did not inhibit the germination of B. sorokinia conidia. The decrease in the antagonistic activity of B. subtilis strains discovered during the studies when cultivated on a nutrient medium containing CS at a concentration of 0.2 % and 0.5 % is apparently caused by its direct negative effect at these concentrations on the growth and development of cultures, which is confirmed by a 10-fold decrease in bacterial cell titers – to 2.2…3.3 × 1010 CFU/ml compared to the initial ones – 1.8…2.2 × 1011 CFU/ml.