Effect of the Salinicola socius SMB35T bacteria on the growth of winter rape at low positive temperature

This study demonstrates the ability of the Salinicola socius SMB35T strain to synthesize the phytohormone indole-3-acetic acid. Moreover, its production depended on the bacterial growth phase. The effect of inoculation with the auxin-synthesizing bacterium S. socius SMB35T on the growth and cold tolerance of winter rapeseed was studied in vitro. The effect was found to be dose-dependent: the use of 40 mg of bacterial biomass for treating 1 g of seeds significantly reduced the height of shoots, and a trend towards a decrease in root length was noted, while the use of bacteria at a concentration two times lower leveled the negative effect and formed a trend towards an increase in the average root length and shoot height. The effect of bacterial treatment of rapeseed on growth (germination and biomass) under cold stress was studied. Seed inoculation with a growth-promoting concentration of the bacterium resulted in a 13.3% increase in seed germination and a 15.1% increase in seedling biomass under cold conditions. However, the use of the S. socius SMB35T strain did not increase the levels of osmolytes, such as sucrose and proline, in rapeseed seedlings. On the contrary, a significant decrease in sucrose content by 35.5% was observed. These results suggest other mechanisms of bacterial-plant interaction that lead to increased cold tolerance in early plant development. Thus, determining concentration specificity and subsequently studying alternative molecular mechanisms of bacterial-plant interactions are key to development of effective microbial preparations.