The Effect of High Temperature Stress on the Occurrence of Dead Heart before and during Flower Bud Differentiation in Garland Chrysanthemum (Chrysanthemum coronarium L.)

Abstract

Garland chrysanthemum (Chrysanthemum coronarium L.) were exposed to 30°C before, during, and after flower bud differentiation to test the effect of the stress on the occurrence of dead heart disorder. 1. Dead heart appeared when the plants at the dome-to late floret-forming stages were placed in an incubator kept at 30°C. No symptoms of dead heart appeared when plants were exposed to the stress during the vegetative or early corolla-forming stages. 2. Application of 0.3% CaCl₂ to shoot tips at weekly intervals decreased the occurrence of dead heart and increased plant height, but had no effect on the rate of flower bud development. 3. Plants with dead hearts at the bolting stage in the spring had smaller statures and flower bud diameters, they had shorter stems but more leaves than had healthy plants. The correlation between the number of injured leaves and total number of leaves on the main stem was significant, whereas there were no significant correlations between the number of injured leaves and plant height, stem length, and flower bud diameter. The correlation between the total numbers of leaves and flower bud diameters were significant in both the plants with and without dead hearts. There was a tendency that the more leaves the plants had, the greater probabilities of their exhibiting dead heart. These results indicate that the dead heart occurs when garland chrysanthemum is a reflection of nutritional competition between a large number of leaves and developing flower parts induced by high temperature.