Reduction of cadmium translocation from roots to shoots in eggplant (Solanum melongena) by grafting onto Solanum torvum rootstock

A Survey in Japan showed that approximately 7%, of eggplant fruits contain cadmium (Cd) concentrations above the international limit for fruiting vegetables. This study was conducted to develop a method to reduce Cd concentration in eggplant fruits. We determined Cd concentrations in eggplants grown oil different rootstocks in Cd-polluted soil, unpolluted soil and nutrient culture. Grafting onto Solanum torvum reduced eggplant fruit Cd concentrations by 63-74% in Cd-polluted soil and unpolluted soil compared with grafting onto Solanum melongena and Solanum integrifolium. Stem and leaf Cd concentrations of scions on S. torvum were approximately 30% of those on S. integrifolium, so Cd translocation from roots to shoots was apparently reduced in plants grafted onto S. torvum. Stern and leaf Cd concentrations of S. torvum were also lower than those of cv. Senryou2 (S. melongena) and cv. Daitarou (S. melongena); thus, Cd translocation from roots to shoots was also reduced in self-rooted S. torvum plants. The Cd concentration of xylem sap in stems of S. torvum was 22% of that in stems of S. melongena, so the reduced Cd translocation from root to shoot could be accounted for by differential loading of Cd into the xylem in roots. We have developed a practical method for reducing the Cd concentration of eggplant fruits by grafting onto S. torvum rootstock. Further investigation is needed to elucidate the mechanism responsible for the low Cd translocation characteristics of S. torvum.