Effects of grafting on root-to-shoot cadmium translocation in plants of eggplant (Solanum melongena) and tomato (Solanum lycopersicum)

Abstract

Heavy metal cadmium (Cd) pollution in farmland has become a serious threat to food security globally. In this work, a grafting technique was applied to eggplant (Solanum melongena) and tomato (Solanum lycopersicum) plants using Solanum torvum as rootstock to investigate effects of grafting on Cd accumulation in shoots. The un-grafted, self-grafted, and grafted plants were grown in soils containing 2 mg kg−1 Cd. Results showed that grafting on S. torvum could efficiently reduce Cd accumulation in leaves of eggplant and tomato, and the decrease was 89% and 72%, respectively. With S. torvum as rootstock, Cd concentrations were 1.11 mg kg−1 and 6.58 mg kg−1 in leaves of grafted eggplant and tomato, which were significantly decreased as compared with un-grafted plants (10.12 mg kg−1 and 23.19 mg kg−1, respectively, p < 0.05). In addition, Cd concentrations were 12.11 mg kg−1 and 29.47 mg kg−1 in leaves of self-grafted eggplant and tomato, respectively, which was similar to those in un-grafted eggplant, but more than those in un-grafted tomato (p < 0.05). This suggests that the S. torvum rootstock, and not the grafting operation, was responsible for efficient reduction of Cd accumulation in shoots of eggplant and tomato plants. Furthermore, total sulfur and sulfate (SO42−) concentrations analysis revealed that there was a similar trend between Cd accumulation and total sulfur or SO42− concentrations in leaves of plants tested. Additionally, a strong positive correlation between Cd accumulation and total sulfur or SO42− concentrations occurred in leaves of eggplant and tomato plants. Thus, sulfur, mainly SO42−, in leaves may play an important regulatory role in Cd accumulation of eggplant and tomato plants. This study provides the theoretical and technical support for applying grafting technique for the safe practice of farming in Cd-contaminated agricultural soil.