Responses of tomato CVs grown to fruit-harvest stage under zinc stress in glasshouse conditions
A glasshouse pot experiment, with three tomato cultivars (CVs), Blizzard, Calypso, and Liberto, was carried out to investigate the effects of three levels of Zn (0.01, 0.5, and 30 mg L-1), supplied in nutrient solution, on plant growth, fruit yield, and nutrient composition. Maximum plant growth and fruit yield in all three cultivars were in the 0.5 mg L-l treatments. Plants treated with Zn at 30 mg L-1 had lower total dry matter content at fruit set as compared with the 0.5 mg L-1 treatment (reduced by 34% in Calypso, 30% in Blizzard, and 21% in Liberto). The percent reduction was similar at the low-Zn treatment (27, 27, and 29%, respectively), and plants exhibited Zn deficiency symptoms. Fruit yield was significantly reduced under both conditions of Zn stress, but only in Calypso was the yield significantly lower at the high rather than at the low-Zn treatment. Zinc concentrations in all plant parts (in particular in roots) increased with increasing Zn concentration in nutrient solution. Concentrations of phosphorus (P), magnesium (Mg), potassium (K), and iron (Fe) in the leaves and fruit of plants grown at 30 mg L-1 Zn were significantly lower than the 0.5 mg L-1 treatment and, with the exception of P in the leaves, lower than in the 0.01 mg L-1 treatment. Zinc stress appears to affect the distribution of macro- and micronutrients in tomato plants with corresponding adverse effects on growth and yield. In this experiment there were no consistent cultivar differences at these zinc concentrations.