عنوان مقاله [English]
Introduction: Carnation (Dianthus caryphyllus L.), from Caryophyllaceae family, is one of the most important cut flowers in the world that its short vase life reduces the economic value. Postharvest longevity of cut flowers can be prolonged using carbohydrates (sugars) in a vase jar. Cut flowers undergo some physiological and biochemical changes that often lead to an early senescence. To delay the aging process in cut flowers, it is necessary to evaluate many aspects of preparation for storage conditions, especially preservative solutions that affect the quality and longevity of these flowers. Many flowers are harvested before they are fully developed, to ensure a long postharvest life and to minimize mechanical damages that might occur during handling. The growth and development of flower buds on cut flowers require food (especially carbohydrates), which is stored in the leaves and stems. These stored carbohydrates can be mobilized for the flower bud to use but maybe they are insufficient when the buds are harvested at a tight-bud stage. To maintain metabolic activities, including respiration, even for cut flowers that have reached full development, it is necessary to provide adequate reserves to achieve acceptable postharvest life. When stored materials are low, leaves and flowers age faster and the petals fade. Under these conditions, supplements can be provided to the flowers by adding sugars such as glucose, fructose and sucrose to the vase solutions. However, it is important to note that a sugar solution is also suitable for the growth of microorganisms, so that an antimicrobial agent should be added to the vase solution as well. Many researches were carried out on prolonging the vase life of cut carnation flowers with different preservative solutions together with an antimicrobial agent. Studies on postharvest longevity of cut carnation flowers using sugars as preservative solutions is low. Therefore, the aim of the present study was to evaluate the effect of sugars (glucose, fructose and sucrose) and application time on vase life and some physiological parameters of carnation cv. “Yellow Candy” cut flowers.
Materials and Methods: A factorial experiment based on completely randomized design in three replicates was performed in order to investigate the effect of different levels (0, 50 and 100 g/L) of three types of sugars (glucose, fructose, and sucrose) and two sugar application times (the first and second 24 h) on vase life of carnation cv. "Yellow Candy" cut flowers. Some other traits such as water uptake, dry mater, relative fresh weight, protein and carotenoid of petal, leaf chlorophyll, POD and SOD enzymes activity and MDA were also measured. The statistical analysis of data was performed using Statistical Package for Social Sciences (SPSS) v 16.0. Least significant difference (LSD) test at P < 0.05 was used to find out the significance of differences among the mean values.
Results and Discussion: Results showed that the effect of different levels of sugars on all evaluated traits was significant. Each three levels of sugars at each two applied times caused to increase vase life and relative traits. Maximum vase life (18 days) was obtained in 50 g/L glucose at the first 24 h with no statistically significant differences with the 100 g/L sucrose and fructose at the first 24 h. The highest water uptakes and dry matter, the lowest POD and SOD activity and minimum MDA were obtained in treatment of 50 g/L glucose at the first 24 h. The highest petal protein content, chlorophyll a, b, and total chlorophyll were achieved in treatment of 50 g/L glucose at the second 24 h. The use of sugars at the first 24 h was more effective in improving the vase life than at the second one. Therefore, application of glucose, preferably in the early hours of harvesting flowers, can be recommended as a prolonged postharvest carnation "Yellow Candy" cut flowers. Positive effect of external holding solutions in vase jar particularly sugars together with an antimicrobial agent on prolonging the vase life of many cut flowers have been shown. Treatment of some cut flowers with sucrose increased glucose and fructose in petals. External sugars can be provided to cut flowers by dissolving a known amount of sugar, along with an antimicrobial agent, into the vase solution. The optimum concentration of sugar varies significantly depending on the flowers being treated. Concentration of 2% sugar is used to keep most flowers in the vase solution. However, some other flowers require higher concentrations, such as 4 to 6%. Some flowers are damaged when treated with concentrations higher than 1%. Therefore, it is important to examine each flower before treating it to determine the optimal concentration of sugars. Sugars are a source of energy and carbon for cut flowers and play an important role in decreasing the protein degradation and ethylene production, maintenance of osmotic balance, increasing water uptake, and finally delaying in senescence process.