Genetic Variation for the Tolerance to NaCl Stress In Relation to CaCl2: Rooted Vs Non-Rooted In Vitro Studies

Micro-propagated plantlets have been used for screening potatoes for salinity (NaCl) tolerance. For this purpose nodal cuttings are placed in media containing varying concentrations of NaCl. Thus ability of the cuttings to induce roots, inpart, determines the tolerance of a given clone to salinity stress. We compared the response of rooted vs non-rooted nodal cuttings to salinity stress. Rooted or non-rooted nodal cuttings of ‘Russet Burbank, Dark Red Norland, Snowden, Atlantic, Supperior’ potato plants were propagated in vitro on a media containing 30 mM NaCl in the presence and absence of CaCl₂ (1mM and 3mM). In addition, these salinity treatments were compared with the response of plantlets to 60 and 80 mM mannitol. Rooted nodal cuttings were produced by growing these cuttings in a normal MS medium for 11 days. These rooted- cuttings were then removed and transferred to media containing various salinity treatments. Ten replicates were used for each treatment and observations were made up to 43 days after transfer to media. Our results show: (i) Under non stress condition transfer of rooted nodal cuttings suffered from a transfer shock (growth inhibition) However this growth reductions was cultivar dependent, Norland and Atlantic being the most sensitive; (ii) Rooted cuttings displayed more tolerance to 30 mM NaCl stress that the non-rooted cuttings; (iii) CaCl₂ mitigated NaCl stress injury in both rooted and non-rooted cuttings; (iv) Injury by NaCl does not appear to be due to osmotic stress. We suggest that rooted cutting may better simulate plant response to saline water irrigation and could be used for screening for salinity tolerance.