The potential of seaweed extracts as a biostimulant for improving salt stress tolerance of Solanum lycopersicum L

Abstract

The present investigation aimed to examine the effects of seaweed extracts (SWE) on tomato plants under saline conditions (50 mM of NaCl). The current findings have shown that the SWE obtained from Jania rubens (J. rubens) gave better results compared to those prepared from the other two seaweeds; Dictyota dichotoma (D. dichotoma) and Gelidium sesquipedale (G. sesquipedale). Indeed, under salt stress, the application of fresh seaweed at 2% significantly (p ≤ 0.05) increased the plant height (26.28 cm ± 0.95) compared with the non-treated stressed control (17.65 cm ± 1.04). Based on these results the effect of J. rubens on some biological and biochemical parameters of tomato plants was evaluated. In fact, increased contents of chlorophylls, total soluble sugars (TSS), and total free amino acids (TFAA) were observed in seaweed-treated plants compared to the control plants. Moreover, the treatment of stressed plants with SWE revealed a significant (p ≤ 0.05) improvement in antioxidant enzyme activities such as superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione S-transferase (GST). The extract also showed an increase in the enzyme activities of glutamate dehydrogenase (GDH) and phosphoenolpyruvate carboxylase (PEPC), which are implicated in the nitrogen and carbon metabolism, respectively. Furthermore, the analysis of the chemical composition of the liquid seaweed extracts (fresh and dried) has shown that they contain bioactive compounds such as polyphenols, flavonoids, soluble sugars, and amino acids, which can be responsible for the tomato's tolerance to salinity. Therefore, the SWE tested in the present study can be used as a biostimulant to enhance the salt stress tolerance of tomato plants.