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

Two tomato (Lycopersicon esculentum) cvs. Blizzard and Liberto, were grown hydroponically in a Controlled Temperature (CT) room for five weeks to inve stigate the effectiveness of foliar application of supplementary iron (Fe) to the leaves of plant grown at high zinc concentration (5 mg L-1). Zinc (Z n) concentrations were 0.5 or 5 mg L-1 in complete nutrient solution. One w eek 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 grow n at 5mg L-1 Zn. The plants grown at 5mg L-1 Zn produced less dry matter an d chlorophyll than those at 0.5mg L-1 for both cultivars. Foliar applicatio n: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 l evels for both cultivars in the high zinc treatment. Application of supplem entary Fe as a foliar spray decreased Zn concentration in the leaves and ro ots of plants grown at high Zn, but its concentrations were still at detrim ental 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 root s. Application of supplementary Fe corrected Fe deficiency in leaves of pla nts grown at 5mg L-1 Zn and reduced root Fe concentrations.