Differential effects of excess calcium applied to whole plants vs. excised fruit tissue on blossom-end rot in tomato

Abstract Blossom-end rot can cause serious yield and quality losses to processing tomato producers, fresh market growers, and home gardeners alike. Blossom-end rot is often associated with calcium deficiency, though salt stress and even high concentrations of calcium salts can also cause blossom-end rot. The goal of this study was to characterize the negative effects of excess calcium compared to inadequate calcium at the whole plant and cellular level. Four calcium chloride levels (0 ppm, 10 ppm, 100 ppm, and 500 ppm) were applied daily to highly blossom-end rot susceptible processing tomato plants, starting at first flowering. Fruit were harvested 21–22 days after pollination. Blossom-end rot incidence and severity were lowest in the 10 ppm treatment. Blossom-end rot incidence was highest in the 0 ppm treatment and blossom-end rot severity was significantly increased in 500 ppm and 0 ppm treatments compared to 10 ppm CaCl2. No significant difference was found in the calcium content of tomato fruit harvested from plants treated with various levels of calcium. The soil drainage solution from the 500 ppm treatment had the highest conductivity, which was nearly 10 times higher than that of the 0 ppm and 10 ppm treatments. Daily plant water use was reduced in the 500 ppm treatment. Application of moderate calcium to tomato plants effectively reduced blossom-end rot incidence and severity, but excess levels of calcium did not reduce incidence and further increased blossom-end rot severity compared to moderate calcium application. Calcium applied to immature tomato fruit pericarp discs also inhibited blossom-end rot symptom development; however, excess calcium did not induce blossom-end rot symptoms. These results indicate that excess calcium induces blossom-end rot development due to effects at the whole plant level, but not due to excess calcium in the fruit tissue.