Effect of nickel and grafting combination on yield, fruit quality, antioxidative enzyme activities, lipid peroxidation and mineral composition of tomato

Soil contamination by heavy metals negatively affects crop productivity, besides representing serious threat to human health. Grafting tomato onto appropriate rootstocks may raise Ni tolerance through limiting heavy metal uptake by roots and/or its translocation to the shoot and by detoxification. A greenhouse experiment was conducted to determine the influence of long-term Ni exposure (0, 25, or 50mM) on crop productivity, fruit quality, leaf chlorophyll content, fluorescence, electrolyte leakage, catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) activities in leaf, proline content, membrane lipid peroxidation, and mineral composition of tomato plants cv. Ikram, either self-grafted or grafted onto three rootstocks: Black Beauty, Unifort, and Maxifort. Significant reduction in yield was observed in response to an increase in Ni concentration with more detrimental effects at 50mM Ni. The fruit dry matter and total soluble solids content increased under severe Ni stress. The depression of crop performance under Ni toxicity was attributed to a decrease in leaf pigments (SPAD index), efficiency of PSII, macro and microelements, and increase in lipid peroxidation and membrane damage. Plants grafted onto tomato rootstocks Maxifort and Unifort exhibited higher chlorophyll content, photochemical activity of PSII, antioxidant activity of APX and GPX, lower accumulation of MDA, and a better nutritional status (higher Ca and Fe, and lower Ni) in the leaf tissues in comparison with selfgrafted plants and those grafted onto Black Beauty. Plants grafted onto tomato rootstocks Unifort and especially Maxifort could minimize the nickel toxicity by improving nutritional status and detoxification processes.