Effect of calcium on yield and incidence of fruit disorders in three tomato cultivars

Greenhouse experiments were conducted in Fall 1995 (1 experiment) and Spring 1996 (2 experiments), which will be referred to as "Experiment 1", "Experiment 2", and "Experiment 3", respectively. Three levels of calcium (low = 20 ppm; medium = 220 ppm; and high = 1,020 ppm; that represented very deficient, normal, and near toxic levels of calcium) were applied to three cultivars of tomato ('Mountain Supreme', 'Celebrity', and 'Sunrise'; selected to represent genetic differences in susceptibility to blossom-end rot (BER)) grown in modified Hoagland solutions utilizing a greenhouse hydroponic system.The source of basic nutrients was a 5-11-26 soluble fertilizer containing micronutrients. The ratio of N-P- K was adjusted to 1.0 : 0.6 ; 2.5 by adding NH₄NO₃ (34% N). Calcium was added as CaCl₂* 2H₂O. In experiment 1 leaf samples were collected below the 1st, 3rd, and 5th flower Clusters. Leaf samples for experiments 2 and 3 were collected above the 1st and 5th flower cluster. Both leaf and fruit calcium contents were analyzed by inductively coupled plasma emission spectrophotometry (ICP). Tomato fruits were harvested 2 or 3 times a week at the breaker stage. Total yield was measured as fruit weight, and marketable fruits were determined based on fruit size and the absence of physiological disorders. Fruits with a diameter > 6.3 cm and free from BER and cracking were categorized as marketable. Leaf and fruit calcium concentrations were increased by the medium calcium treatment. Leaf calcium concentration did not significantly differ among the tomato cultivars studied. Fruit calcium concentration responses of the three cultivars were different between Fall and Spring experiments. In experiment 1 (Fall 1995), across treatments 'Mountain Supreme' had a higher fruit calcium concentration than 'Celebrity'. No significant differences in fruit calcium occurred in experiments 2 and 3 (Spring 1996). In all the experiments conducted, the medium calcium treatment reduced the incidence of BER. The total weight of marketable fruit was not affected by the medium calcium treatment in experiment 1, but it was increased by the medium calcium treatment in experiments 2 and 3. In all three experiments the high calcium treatment reduced the total fruit weight per plant, average fruit weight, total weight of marketable fruit per plant, and average marketable fruit weight. 'Celebrity', across treatments, was consistently more susceptible than 'Mountain Supreme' to incidence of fruit disorders.