Response of some tomato cultivars to sodium chloride stress under in vitro culture condition.

The response of calli of six tomato cultivars (Lycopersicon esculentum Mill.) to salt stress was investigated under in vitro conditions. Callus relative growth rate (RGR), dry matter percentage (DM), osmotic potential and proline content were evaluated. Significant differences were found among cultivars regarding above traits. ‘PS-10’ had the highest RGR, while ‘Roma’ had the lowest amount of this trait under salt levels. Any increase in salinity levels in the media led to decrease of RGR and in contrast increased DM and osmotic potential in all treatments compared to control. In all cultivars, proline levels increased in response to salinity stress. High callus formation was correlated with low proline content. ‘PS-10’ and ‘Imperial’ had the highest callus formation and the lowest proline content. Significant differences were recorded in regeneration potential of cultivars under salt treatments. ‘PS-10’ possessed the highest and ‘Roma’ had the lowest regeneration rate. It is concluded that the more the salt tolerant genotype the more is the reduction in osmotic potential and proline content.   Key words: Tomato, callus, in vitro, sodium chloride stress.