  Wild populations of Medicago ciliaris and Medicago polymorpha were subjected
to four salt treatments 0, 50, 100 and 150 mM NaCl, plant growth and proline
concentration in leaves were assessed. The analyzed data revealed significant
variability in salt response within and between the two species, depending on
the salinity level. It was found that high NaCl concentrations affected all the
growth parameters. However, the reduction was more important at higher NaCl
concentrations and the highest reduction was obtained for the populations of
Medicago polymorpha where it reached around 90% in root length at 150 mM NaCl
for Pmar. The Tunisian population of Medicago ciliaris, prospected on soils
affected by salinity, was the best tolerant in all ecotypes studied in this
work. This population, exhibits a particular adaptability to salt environment
at both germination and seedling stage. Furthermore, the correlation among the
studied plants sensitivity and leaf proline concentration showed that high
proline contents were related to their reactivity to salt. Consequently, it
appeared that proline biosynthesis occurred presumably as a consequence of
disturbance in cell homoeostasis and reflected poor performance and greater
damage in response to salt stress. These findings indicated that this osmolytes
content may be used as another useful criterion to differentiate salt-tolerant
from salt sensitive plant in annual medics.
