Rapid Leaf Senescence Symptoms Are Related to Carbohydrate Depletion in Cut Chrysanthemums, and Strategies for the Symptoms Reduction

Chrysanthemum (Chrysanthemum ×morifolium) is the second-largest exported cut flower worldwide; however, some cultivars exhibit rapid leaf senescence during their first week of vase life. This phenomenon negatively impacts consumer perception of plant quality, and its cause has been unknown. Experiments were performed in Colombia on cut chrysanthemums shipped to the U.S. for vase-life evaluation. After 10 d, the severity of leaf senescence symptoms was recorded. Experiments examined the effect of flower form [disbud (one flower per stem) versus spray (5-10 flowers per stem)], the effect of time of harvest (A.M. versus P.M.), and sugar sources (dextrose, fructose, mannitol, and sucrose) at different concentrations in vase solutions on senescence symptom development. Results showed that spray-form stems showed higher leaf senescence severity than disbud-form stems; morning harvest increased symptom severity compared to noon harvest; stems placed in a vase solution without sugars displayed more severe symptoms than stems treated with sugars in the vase solution except for mannitol treatments. Carbohydrate concentrations in leaves were collected throughout the experiment. Results showed starch, glucose, fructose, and sucrose reduction from harvest through storage and shipping until the stems were placed in vase solutions. In summary, the results demonstrate that the rapid leaf senescence of chrysanthemums is related to carbohydrate depletion in the leaves during the postharvest environment. Postharvest treatments such as hydration time and environment, the application of plant growth regulators, sucrose in the hydration solution, post-shipping holding solution, and vase solutions were evaluated. The most effective strategies for reducing leaf senescence symptoms for most of the cultivars evaluated were afternoon harvesting, adding plant growth regulators, such as thidiazuron, and a mixture of cytokinins and gibberellic acid at 10 or 20 ppm in the hydration solution for 4 h after harvest, and the addition of 0.025 and 0.05 g/mL sucrose into vase solutions