Low sodium chloride priming increases seedling vigor and stress tolerance to Ralstonia solanacearum in tomato

Abstract

Seed germination is the initial step of seedling development in plants. Seed priming with salts has been used to synchronise seed germination. In general, a long-term treatment with a relatively high salt concentration, such as 1 M NaCl, is employed. To improve the efficiency of this treatment, we examined the effect of seed priming with a lower NaCl concentration than conventional method in tomato (Solanum lycopersicum). Tomato seeds were soaked for 24 h at 25°C in the dark in 100–1000 mM of NaCl solution (NaCl-priming) or distilled water (hydro-priming). To estimate the effect of NaCl-priming on seed germination and subsequent seedling growth, the germination rate, seedling emergence, plant height, and hypocotyl and root length were investigated under NaCl-, hydro- and non-priming treatments. At 4 d after sowing, the seedling emergence was markedly promoted by 300 mM of NaCl-priming. The NaCl-priming also significantly enhanced the seed germination rate at 48 h after sowing. Seedling growth, as indicated by plant height, stem diameter and hypocotyl and root length, was promoted by NaCl-priming. These results suggest that priming with low saline has similar effects as conventional priming methods. A comprehensive gene expression analysis showed that the genes related to seedling growth and stress responses were up-regulated by NaCl-priming at 144 h after the start of the treatment, followed by advanced and uniform seed germination. The seedlings exhibited an increased tolerance to Ralstonia solanacearum, the causative agent of bacterial wilt of tomato, compared with the hydro-primed and non-primed seedling.