Influence of Bacillus subtilis bacteria on growth and development of horse mint (Mentha longifolia L.) and lemon balm (Melissa officinalis L.) under hydroponic cultivation

The aim of the study is to evaluate the effect of Bacillus subtilis bacteria (strains 104 and 26D) on the growth and development of medicinal plants (Mentha longifolia L. and Melissa officinalis L.) when grown hydroponically in closed agroecosystems. Strains 104 and 26D B. subtilis had different effects on growth processes (increase in the area and number of leaves, biomass gain), as well as on the content of photosynthetic pigments. Treatment with strain 104 had the most effective effect on productivity, increasing biomass gain by 84.0 % in horse mint and by 52.8 % in lemon balm compared to the control plants. The highest concentration of Chl a, Chl b and total Chl(a+b) (10.60, 3.66 and 14.26 mg/g wet biomass, respectively) was observed in mint leaves treated with B. subtilis 26D, while in lemon balm the maximum accumulation of chlorophylls was observed in B. subtilis 26D and 104 compared to the control. These data indicate that the effect of the bacterial culture on plants is speciesspecific. That is, the treatment with B. subtilis (strains 104 and 26D) does not cause the same effects or reactions to the same extent in the studied plants, the responses are characteristic of an individual combination of plants and bacteria. Understanding these processes will help to develop effective methods for increasing the productivity and quality of essential oil crops under controlled cultivation conditions.