Plant Probiotic Endophytic Pseudomonas flavescens D5 Strain for Protection of Barley Plants from Salt Stress

Soil salinity has become a global issue that is directly related to land degradation and results in many changes in climate, ecosystem services, and biodiversity. The present study focuses on the investigation of beneficial properties of a plant probiotic bacterial strain as an eco-friendly and sustainable approach to promote crop growth in saline soil. The endophytic halotolerant strain Pseudomonas flavescens D5 isolated from common chicory (Cichorium intybus L.) was able to grow on a medium containing 15% NaCl; produced indole-3-acetic acid (45.2 mu g mL(-1)) and polyhydroxyalkanoate (1.72 g L-1); and had amylolytic, cellulolytic, and proteolytic activities. Polyhydroxyalkanoate had a pronounced antifungal activity against Fusarium graminearum, F. solani, F. oxysporum, and Alternaria alternata. Under salt stress conditions, inoculation with Ps. flavescens D5 increased the shoot biomass of barley plants by 8-30%, root biomass by 7-20%, chlorophyll a by 18-52%, and chlorophyll b by 7-15%. The content of proline decreased by 1.5-1.8 times. An increase in the activity of antioxidant enzymes (catalase, guaiacol peroxidase, and ascorbate peroxidase) was determined. In inoculated plants growing in saline soil, the content of Na+ ions was lower by up to 54.8% compared to control. This strain is promising for stimulating plant growth and protecting them from diseases and other adverse environmental factors, including salt stress.