Calcium amendment and NaCl salt pre-treatment improves salinity tolerance in potato genotypes
Pre-exposure to low but non-toxic levels of calcium and NaCl salt have been demonstrated to ameliorate the adverse effects of subsequent NaCl stress on plant growth and nutrient uptake. The effect of CaCl2, NaCl and CaCl2 + NaCl on subsequent salt stress tolerance, growth, water status and ion accumulation of four contrasting potato genotypes, 9506, ‘Norland’, ABA-deficient mutant and ABA normal sibling were investigated to provide an additional tool to induce NaCl salt stress tolerance. NaCl pre-treatment was generally the most effective in inducing salt stress resistance reflected by positive response measurements in all genotypes. ‘Norland’ and ‘9506’ enhanced growth up to 70% via root mass under salt stress and expressed elevated water status under NaCl pre-treatment, possibly via Na+ accumulation in the roots. Unlike ‘Norland’, the 9506 genotype also tolerated the presence of Na+ in the shoot. However, NaCl was excluded from the shoot of ‘9506’ after CaCl2 pre-treatment and may indicate a genotype-dependent Ca+2 requirement for Na+ exclusion. In the ABA normal sibling, salt stress resistance was largely regulated by two mechanisms under all pre-treatments: a) shoot Na+ exclusion and root Na+ accumulation; b) enhanced water status which was expressed by an elevation of leaf and shoot water content. This response to pre-treatment was facilitated by: a 40% - 100% increase in root mass, enhanced K+ uptake into the roots, enhanced K+/Na+ ratio in the root and shoots and increased leaf osmotic potential. The ABA-deficient mutant expressed only one mechanism of salt stress resistance in response to pre-treatments in which leaf and shoot water content increased. That the pre-treatments of the ABA-deficient mutant were not able to adequately increase shoot K+ and exclude Na+ from the shoot relative to the ABA normal sibling and other genotypes suggests that ABA is a requirement for this mode of salt stress defence.
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