Abstract
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.
Highlights
Under natural conditions, plants are subjected to several types of environmental stress
At 0 mM NaCl, seed germination was delayed by 1 day for Acacia cyanophylla, Acacia ampliceps, Medicago arborea and Hedysarum carnosum, by 3 days for Ceratonia siliqua and by 4 days for Casuarina glauca
The effect of salt stress on the delay in germination was reported for others halophytic plants species like Atriplex lentiformis, where the speed of germination is slower in salinity treatments than in control (Mahmood, 1995)
Summary
Plants are subjected to several types of environmental stress (biotic, abiotic). Salinity in the soil is one of the non-living environmental stresses that affect crop production especially in arid and semiarid regions. Plants can develop strategies to grow in saline environments, but after successful seed germination, which is a key stage for plant establishment (Sattar et al, 2010). Salt stress is one of the most serious environmental factors limiting the germination of seeds and the growth of plants due to affecting the water and mineral status of the seeds and/or plants that leads to osmotic stress and an excess of sodium ions. Increase in salinity levels causes a reduction in seed germination percentage and delay germination process initiation, while salt stress can cause complete inhibition of the germination process (Pujol et al, 2000)
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