Foliar application of iron as a remedy for zinc toxic tomato plants

Abstract

Two tomato [Lycopersicon esculentum) cvs. Blizzard and Liberto, were grown hydroponically in a Controlled Temperature (CT) room for five weeks to investigate the effectiveness of foliar application of supplementary iron (Fe) to the leaves of plant grown at high zinc concentration (5 mg L⁻¹). Zinc (Zn) concentrations were 0.5 or 5 mg L⁻¹ in complete nutrient solution. One week after application of Zn at 5 mg L⁻¹, supplementary iron ( 28 mg L⁻¹ for a week and 56 mg L⁻¹ for a week) was supplied via leaves to the plants grown at 5mg L⁻¹ Zn. The plants grown at 5mg L⁻¹ Zn produced less dry matter and chlorophyll than those at 0.5mg L⁻¹ for both cultivars. Foliar application of supplementary iron resulted in increases in dry matter and chlorophyll concentrations for both cultivars. These increases were greater in Liberto than in Blizzard. Zinc concentration in plant tissues increased to toxic levels for both cultivars in the high zinc treatment. Application of supplementary Fe as a foliar spray decreased Zn concentration in the leaves and roots of plants grown at high Zn, but its concentrations were still at detrimental levels. Iron concentration in leaves declined to the deficient level in the high (5 mg L⁻¹) Zn treatment, but was markedly increased in the roots. Application of supplementary Fe corrected Fe deficiency in leaves of plants grown at 5mg L⁻¹ Zn and reduced root Fe concentrations.