Improvements in physiological and nutritional developments of tomato cultivars grown at high zinc by foliar application of phosphorus and iron
Tomato (Lycopersicon esculentum) cvs. "Blizzard", "Liberto", and "Calypso" were grown hydroponically in a controlled temperature (C.T.) room for five weeks. The objective was to investigate the effectiveness of foliar-applied phosphorus (P) and iron (Fe) (SPFe) sprayed to the leaves of seedlings grown at high (77 μmol L) zinc (Zn). Zinc concentrations added to nutrient solution were 7.7 or 77 μmol L. One week after application of root zone Zn at 77 μmol L, SPFe at 10 and 0.5 mmol L, respectively, were sprayed on the leaves of seedlings in high zinc treatment twice a week for three weeks. Significant reductions in dry weight, chlorophyll contents and daily water use were recorded for the seedlings grown at 77 μmol L Zn compared with those at 7.7 μmol L for all three cultivars. Membrane permeability (electrolyte leakage) increased in the seedlings grown at 77 μmol L Zn compared to 7.7 μmol L. The SPFe as a foliar application led to significant increases in dry weight, chlorophyll concentrations and daily water use for all three cultivars. Membrane permeability, based on electrolyte leakage, impaired by high zinc was maintained with SPFe treatment. Leaf Zn increased to toxic levels for all three cultivars in the high Zn treatment. The SPFe lowered zinc concentrations in the leaves and roots of seedlings grown at high Zn, but concentrations of Zn were still at critical toxic levels. Leaf P and Fe declined to deficient levels in the high (77 μmol L) Zn treatment, but were significantly increased in the roots. SPFe corrected both P and Fe deficiencies in leaves of seedlings grown at 77 μmol L Zn and reduced root P and Fe concentrations.