Effect of grafting on the growth and ion concentrations of cucumber seedlings under NaCl stress

To assess whether grafting raised the salt tolerance of cucumber seedlings by limiting transport of Na+ to the leaf and to test whether the salt tolerance of grafted plants was affected by the shoot genotype, two cucumber cultivars (Jinchun No. 2, a relatively salt-sensitive cultivar, and Zaoduojia, a relative salt-tolerant cultivar) were grafted onto rootstock pumpkin (Cucurbita moschata Duch. cv. Chaojiquanwang, a salt-tolerant cultivar). Ungrafted plants were used as controls. The effects of grafting on plant growth and ion concentrations were investigated under NaCl stress. Reductions in the shoot and root dry weights, leaf area and stem diameter of grafted plants were lower and concentrations of K+ and Cl- in the leaves were higher than those of ungrafted plants under the same NaCl stress. The Na+ concentration and Na+/K+ ratio in scion leaves and in the stems of grafted plants were lower, whereas those in rootstock stems and roots were higher than in ungrafted plants under the same NaCl stress. Shoot and root dry weight, leaf area and stem diameter were negatively correlated with leaf Na+ concentrations and Na+/K+ ratio, but were positively correlated with leaf K+ concentrations. The Na+ concentrations and Na+/K+ ratio were lower, whereas the K+ concentrations in the leaves of grafted Zaoduojia plants were higher than those in grafted Jinchun No. 2 plants under the same NaCl stress. The reductions in leaf area and stem diameter of grafted Jinchun No. 2 plants were more severe than those of grafted Zaoduojia plants. These results indicate that: (1) the higher salt tolerance of grafted cucumber seedlings is associated with lower Na+ concentrations and Na+/K+ ratio and higher K+ concentrations in the leaves, (2) grafting improved the salt tolerance of cucumber seedlings by limiting the transport of Na+ to the leaves, (3) the salt tolerance of grafted cucumber seedlings is related to the shoot genotype.