In Tunisia, more particularly in semiarid and arid areas, the drought accentuated by the surface evaporation of water lead to gradual increase in salinity of the soil which a major hurdal in development of vegetation. In these highly salted ecosystems, some plants are growing naturally; however, various species show different tolerance levels to salinity during their development. Seed germination is the stage which is most susceptible to this abiotic constraint. The aim of this study is to investigate the influence of increasing NaCl concentrations from 0 to 200 mM on the germination behavior of some halophytic plants species (Acacia cyanophylla, Acacia ampliceps, Medicago arborea, Hedysarum carnosum, Casuarina glauca and Ceratonia siliqua) whose seeds, were collected from Tunisian stands. The germination is evaluated through the daily and the cumulated rates of germination, the corrected seed germination rate and the recovery rate. The effect of salt stress revealed that the elevation of NaCl concentration induces a reduction of germination capacity as good as germination speed. In this setting, 200 mM concentrations of NaCl constitute a physiological limit of germination for all studied species. However, the interspecific variability is relatively important. According to the principal component analysis (PCA), seeds of C. glauca were the most salt tolerant, followed by M. arborea. Seeds of A. ampliceps were the least salt tolerant. The increase of the recovery rate with high salinity supposed that the latter has an osmotic reversible effect and not a toxic irreversible one on the studied species seeds.
Key words: Halophytes, salt stress, germination, Tunisia.
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