Improving the Antioxidants System, Growth, and Sugar Beet Quality Subjected to Long-Term Osmotic Stress by Phosphate Solubilizing Bacteria and Compost Tea

Abstract

Water stress alongside soil salinity constraint the productivity of crops. Application of beneficial microbes and natural extracts are considered new effective strategies used to develop plant adaptation under abiotic stress. Sugar beet plants were treated with phosphate solubilizing bacteria (PSB) and compost tea (CT), in a 2-year field experiment to explore the potential role of PSB, CT, and PSB + CT in enhancing plant growth, physiology, productivity, and sugar quality of sugar beet plant subjected to three watering regimes (1-well-watering (WW), 2-moderate drought (MD) and 3- severe drought (SD)) in salt-affected soil. Drought stress either under MD or SD conditions augmented ion imbalance followed by reducing the relative water content (RWC), relative membrane stability index (RMSI), stomatal conductance (gs), and chlorophyll content, which conflicted on the vegetative growth, root yield, sugar yield and quality. However, there were increases in osmolytes and activity of enzymatic antioxidants. Application of CT is more effective than PSB in motivating the activities of CAT, POD, SOD enzymes, and total soluble sugars (TSS). In contrast, CT application under MD conditions reduced glycine betaine (GB) and proline levels, reflecting on promoting the growth, physiological functions, and yield, subsequently restoring their levels under WW conditions. The combined treatment PSB + CT under moderate drought reduced GB and proline levels and enhanced the antioxidant system, RWC, RMSI, gs, chlorophyll, TSS, total leaves area, root length, root diameter, root yield, sugar yield, and quality. All types of additions under severe drought could not restore the yield of root and sugar to their levels under well-watering conditions. It was concluded that the coupled application of PSB and CT has beneficial effects on growth and quality of sugar beet growing under moderate drought in salt-affected soil.