Determination of salinity tolerance threshold in six medicinal plants

The effects of salinity on seed germination and tolerance of six medicinal plants were investigated. The experiment was factorial based on completely randomized designs with three replications. The first factor was salinity in five levels and second one was in six medicinal plants (Artichoke, Milk thistle, Fennel, Black cumin, Safflower and Flax). Salinity tolerance threshold for germination percentage in Artichoke, Milk thistle, Fennel and Black cumin was 4, 3.3, 10.6 and 16.5 ds m-1, respectively. But germination percentage in Safflower and Flax reduced very slowly and the amount of germination percentage was high (88 and 87 percent, respectively) under maximum salinity stress (22.22 dsm-1). Germination rate under salinity stress decreased linearly. Overall, dry weight and length of seedling reduced by the influence of salinity stress in seedling stage but salinity tolerance threshold and reduction ratio of these components were different in the plants. The results of cluster analysis showed that plants in stage of germination are categorized three groups: Safflower and Flax (tolerant to salinity), Fennel and Black cumin (moderately tolerant to salinity), Artichoke and Milk thistle (sensitive to salinity). The cluster analysis in the seedling stage showed that plants divided to four groups: Safflower (tolerant to salinity), Artichoke and Milk thistle (moderately tolerant to salinity), Fennel (moderately tolerant to salinity) and Black cumin and Flax (sensitive to salinity).