A plant-based biostimulant approach to improve salt stress tolerance in tomato: The role of Hypericum heterophyllum Vent. extract

Salt stress severely limits seed germination and early seedling establishment in tomato. Plant-derived extracts have recently attracted attention as eco-friendly biostimulants capable of enhancing stress tolerance. The present study investigated the effects of different concentrations of Hypericum heterophyllum whole-plant extract on seed germination, seedling growth, and changes in physiological and biochemical parameters in tomato under salt stress. Tomato seeds were primed with aqueous H. heterophyllum extract at 0.25, 0.5, 1, and 2% (w/v) and subsequently exposed to NaCl-induced (200 mM) salinity stress. Germination percentage, mean germination time, root and shoot length (at early and late seedling stages), membrane damage, total chlorophyll content, and total flavonoid and phenolic contents in tomato leaves were evaluated. Salt stress markedly reduced germination and seedling growth, whereas H. heterophyllum extract treatments significantly alleviated these inhibitory effects in a concentration-dependent manner. The 0.5% and 1% extract concentrations were the most effective in improving germination performance and seedling growth under salt stress. These treatments also decreased membrane damage and increased total chlorophyll content. Moreover, increasing extract concentration led to higher total phenolic and flavonoid contents under salt stress. Overall, these findings suggest that H. heterophyllum extract has strong potential as a natural biostimulant and could be considered a promising, sustainable strategy to enhance salt stress tolerance and improve crop establishment in agricultural production.