Diversity of Salt Tolerance During Germination in Medicago ciliaris (L.) and Medicago polymorpha (L.)

Abstract

Variability of salt tolerance in eight wild populations of two annual Medicago species (Medicago ciliaris and Medicago polymorpha) was evaluated at germination stage using tree treatments of salinity: 50, 100 and 150 mM of NaCl. Results showed that germination is clearly affected by high salt stress; their germination rate doesn’t exceed 7% at 150 mM. The greatest variability in tolerance was observed at moderate salt stress (50 mM of NaCl) and the decrease in germination seems to be more accentuated in Medicago polymorpha than Medicago ciliaris. Whereas, the Tunisian population of Medicago ciliaris was the best tolerant in all ecotypes studied in this work. This population prospected on soils affected by salinity, exhibits a particular adaptability to salt environment, at least at this stage in the life cycle. This intra-specific variation in salt tolerance may be used to select genotypes particularly suitable for cultivation on lands relatively affected by salinity. On the other hand, when ungerminated seeds from NaCl treatments were transferred to distilled water, they recovered largely their germination at all the populations studied after only 2 days. This, indicate that the germination inhibition was related to osmotic stress rather than ion toxicity. In addition, seed germination in all populations tended to be extremely rapid than that observed in distilled water which indicate that this pretreatment raises dormancy.