Seaweed Extract Improves Growth and Productivity of Tomato Plants under Salinity Stress

Biostimulants constitute an emerging group of crop management products used to enhance productivity under abiotic stress conditions. The ability of some biostimulant products, such as seaweed extracts (SE), to enhance crop tolerance to salinity stress has been documented. SE contain a series of bioactive compounds and signaling molecules, as well as mineral and organic nutrients, that greatly benefit plants. A greenhouse experiment was conducted in order to evaluate SE-mediated tolerance mechanisms in tomato plants under salinity stress. The experiment was divided into two developmental phases (vegetative and reproductive) and included four treatments: control (plants with neither treatment), SE (plants treated with seaweed extract), NaCl (plants irrigated with 300 mM NaCl), and SE + NaCl (plants treated with seaweed extract and irrigated with 300 mM NaCl). Tomato plants treated with the SE from Padina gymnospora showed an increase in root and shoot length (18 cm and 13 cm), root and shoot area (33 cm2 and 98 cm2), and shoot and root fresh weight (1.0 and 3.8 g) under the control and salinity stress conditions. The decrease in productivity (number of fruits) associated with salinity stress was reduced from 28.7% to only 3.4% in SE-treated plants. The positive effects of SE application also included early flowering and enhanced fruit weight and quality. Our findings suggest that optimized photosynthetic performance and antioxidant defense systems (proline, total phenols, and flavonoids) appear to be major factors modulating SE responses to salinity tolerance in tomato plants with promising agricultural applications.