RESPONSE OF ALFALFA CULTIVARS TO SALINITY DURING GERMINATION AND POST-GERMINATION GROWTH

During post-germination growth, alfalfa (Medicago sativa L.) cultivars may exhibit a different salinity tolerance from that expressed during germination. To explore this possibility, 86 cultivars and experimental populations of alfalfa were exposed to nine levels of NaCl ranging from 0 to 342.2 mM during germination. Cultivars that exhibited the highest (14 cultivars) and the lowest (8 cultivars) NaCl tolerance from the germination study were exposed to 0, 88, and 132 mM after the completion of germination under 0 NaCl to determine post-germination NaCl tolerance. There were no significant correlations between percent germination of these cultivars at 88 or 132 mM NaCl and their subsequent growth parameters. The IC50, or the NaCl concentration that inhibited germination of 50% of the viable seeds, of the cultivars was negatively correlated only with shoot-to-root ratio when the plants were exposed to 132 mM NaCl after germination. Post-germination performance of cultivars that needed high NaCl concentration to inhibit 50% of their seed germination (high IC50 group) was not significantly different from the low IC50 group under 88 or 132 mM NaCl treatments. The ability of alfalfa cultivars to germinate at high NaCl concentrations was not related to their post-germination performance under salt stress, except for the negative correlation between IC50 and shoot-to-root ratio at 132 mM.