Chloride Salts and Light Modulate Germination and Early Seedling Performance in Dittrichia viscosa

Soil salinity is one of the main environmental factors limiting plant germination and establishment, particularly in Mediterranean ecosystems. This study evaluated the germination, recovery, and early development of Dittrichia viscosa exposed to NaCl, KCl, CaCl2, MgCl2, and an equimolar mixture (0–360 mM) under a 12 h light–dark regime and continuous darkness. In the absence of salt, final germination was similar under both regimes, although it was faster in the dark. Increased salt concentration reduced and delayed germination, depending on the type of salt and the light regime used. KCl maintained the highest germination percentages under the light–dark regime at 90 and 180 mM, whilst CaCl2 and MgCl2 were the most inhibitory individual salts at 180 mM. The salt mixture was the most restrictive under both regimes. Following transfer to a salt-free medium, ungerminated seeds showed a high rate of recovery even after exposure to the highest concentrations of individual salts, indicating that the inhibition was largely reversible. The first two components of the principal component analysis (PCA) explained 71.89% of the variation, linking germination and its rate to seedling vigour. Overall, D. viscosa showed considerable germination tolerance to individual salts but high sensitivity to their combined action.