Impact of Grafting, Salinity and Irrigation Water Composition on Eggplant Fruit Yield and Ion Relations

Scarcity of fresh water in arid and semi-arid regions means that we must use more saline waters for irrigation and develop tools to improve crop salt tolerance. The objectives of our study were to (1) Evaluate fruit production, salt tolerance and ion composition of eggplant cv Angela, both nongrafted and when grafted on tomato cv Maxifort rootstock and (2) Evaluate eggplant specific toxicity effect of Cl^- and Na⁺ ions under saline conditions. We salinized the irrigation water with either a Na⁺-Ca²⁺- Cl^- composition typical of coastal Mediterranean ground waters as well as a mixed Na⁺-Ca²⁺-SO₄^2- Cl^- type water, a composition more typical of interior continental basin ground. For each water type we evaluated 5 different salinity (osmotic) levels of -0.003 (control), -0.15, -0.30, -0.45 and -0.60 MPa. There were no statistically significant differences in the fruit yield relative to the water type, indicating that Cl^- ion toxicity is not a major factor in eggplant yield associated with salinity. This conclusion was confirmed by the determination that leaf Cl content was not correlated with relative yield. The electrical conductivity of the saturation extract (EC_e) at which yield is predicted to be reduced by 50% was 4.6 dS m^-1 for the grafted plants vs. 1.33 dS m^-1 for the nongrafted plants. The relative yield was very well correlated to leaf Na concentrations regardless of grafting status, indicating that Na is the toxic ion responsible for eggplant yield loss under saline conditions. The increased salt tolerance of cv Angela eggplant when grafted onto tomato Maxifort rootstock is attributed to a reduced Na uptake and increased Ca and K uptake with Maxifort rootstock.