Introduction
Vase life of cut gerbera flowers often ends due to scape bending that precedes the wilting of ray flower. In addition, vase life of cut gerbera ends when started to showing ray flower drop, wilting, curling, and discoloration.
Scape bending is the main reason of shortening vase life of cut flower of several gerbera cultivars (Kim et al. 2004). Cut gerbera flower produced in Korea is fixed with a metal pin into the scape and then taped to protect scape from bending and these increase the postharvest cost (Yoon et al. 1996). Scape bending has been related to lack of mechanical support in the scape of cut gerbera flower (Perik et al. 2012). One of general cause of cut flower death is breakdown of cells and membranes and their loss of vital functions (Rogers 1973). Cell walls determine the mechanical strength of the plant structure (Cosgrove 2005).
Vase life of gerbera was affected by scape hardness, so several studies to extend vase life of gerbera through preand postharvest calcium chloride (CaCl2) treatments were carried out and obtained the result of prolonging vase life through reducing scape bending (Perik et al. 2012). But the effect of external calcium treatment on hardness of gerbera scape is not still clear related to calcium movement to cellular tissue. It might be due to calcium ions binding with pectin and increasing cell wall hardness (Madani et al. 2014), but the effect of calcium on pectin fractions of gerbera scape has not yet been described.
Therefore, this experiment was conducted to investigate the correlation between calcium and pectin in gerbera scape bending. Ornamental value loss of cut gerbera was divided into two kinds of type, scape bending and not bending.
Materials and Methods
Plant material
Gerbera ‘Harmony’ was bred by the National Institute of Horticultural and Herbal Science, Rural Development Administration, in 2010 (Park et al. 2013). It has been grown at the greenhouse, University of Seoul, since October of 2014. Plants were cultivated in coir media by Netherland nutrient solution and were drip-irrigated five times per day. Flowers were harvested at optimum commercial maturity of showing two outer mature stamens (De Jong 1978).
After harvest, flowers were transported wet to the laboratory in one hour. Flowers were 11 ± 1 cm of flower head diameter and scape length of 60 ± 5 cm. Flowers were placed in glass bottles about 23 cm in height. These bottles were contained 250 mL of distilled water and placed in a environmental-controlled growth chamber (HB-301SP, Hanbaek scientific CO., Korea): 24.8 ± 0.8℃ air temperature (AT), 26.3 ± 1.3% relative humidity (RH), 1,250 μmol·m-2·s-1 PPFD under fluorescent light, and 12h photoperiod. The experiment was for 2 weeks, from 25 July to 2 August.
Determination of Vase life
The vase life started as soon as harvest and counted until flowers started showing symptoms of ray flower drop, wilting, curling, discoloration, and scape bending (Kim et al. 2004). When flowers lose their ornamental value, the vase life was finished (Park and Cho 2004). The scape bending defined as over 90 ° in s cape angle was measured every day.
Cation and pectin contents in scape
The scape was cut in 5 equal lengths (S1 to S5) and each scape section was wet digested in 50% HClO4-H2SO4 according to RDA (2013). Cation content of each scape section was measured by an atomic absorption spectrophotometer (Analyst 400, Perkin-Elmer Co., USA). Pectin contents were analyzed using modified carbazole colorimetric method according to Bitter and Muir (1962). 0.5 mL of each water soluble pectin fraction (WSP) and water insoluble pectin (WIP) fractions were mixed with 3 mL of H2SO4 and cooled in r efrigerator, then heated in water b ath at 30℃. After 1 0 minutes, 0.1 mL of carbazole reagent was added and it was left for 2 hours for maximal color development. The absorbance of sample was measured at 530 nm wavelength using UV-VIS spectrophotometer (UV-2450, Shimadzu, Japan).
Statistical analysis
Results were compared by analysis of variance (ANOVA) using the SAS statistical software package (Statistical analysis system version 9.4, SAS Institute Inc. Cary, NC). The Duncan’s New Multiple Range Test (DMRT at P < 0.05) was used for comparisons of treatment means.
Results and Discussion
Vase life and postharvest quality
Vase life of cut gerbera was reduced to half (7.2 to 3.6 days) when scape bending occurred (Table 1). This result was similar to previous study in which scape deformation reduced the vase life of 10 cultivars of cut gerbera (Kim et al. 2004). Fresh weight of cut flowers was not different regardless of scape bending occurrence. At the end of vase life, the angle of bending scape was 101.6° whereas that of not bending scape was 38.4° (Table 1). Scape bending occurred mainly at the section of S1 and S2 of flowering scape. The result coincides with previous research showing that scape bending occurred at about 12 cm below the floral head in 45 cm length of scape of cut gerbera (Perik et al. 2012).
For scape diameter and dry weight at the end of vase life, there were no distinct differences among the types of ornamental value loss. But there was significant difference in scape section as the upper sections of scape were to be thinner and lighter than the lower sections (Table 2). When scape bending occurred, the scape hardness in the all sections was decreased, typically in S1 (0.32 to 0.24 kg) and S2 (0.37 to 0.31 kg) sections of scape (Table 2). Scape diameter and dry weight were no significance among the types of ornamental value loss but significance was found in scape hardness. From all measurements, significance was found in scape sections. There was no significance when considering both types and sections (Table 2).
Scape bending occurred mostly in the S1 and S2 sections of the scape due to decline in scape hardness. Previous studies on cut gerbera revealed that the upper parts of gerbera scapes had fewer vascular bundles and less lignin and cellulose content compared to the lower parts of scape (Marousky 1986), and that younger cells in the upper scape continue to elongate after harvest, but are unable to develop stable cell wall (Steinitz 1982). These factors may attribute to lower scape hardness in upper parts of gerbera scape, which lead to bending. In case of roses, stem bending occurred more frequently in cultivars with lower stem hardness (Kim and Lee 1996).
Cation and pectin contents in scape
Table 3 showed the composition of cations in cut gerbera at the end of vase life. Potassium contents were not significant in each scape section or the type of ornamental value loss. While magnesium contents were not different from the type of ornamental value loss, those were showed the significant difference among each scape section and the highest magnesium content was observed in the S1 section. Calcium contents were generally decreased when scape bending occurred. The most decline of calcium content was 2.9 mg·L-1 in the S1 section, followed by 2.6 mg·L-1 in the S2 section. Cho (2005) reported that gerbera cultivars with shorter vase life were lower calcium content in scape compared to gerbera cultivars with longer vase life, but potassium and magnesium contents were no difference among gerbera cultivars. It is suggested that damage to the scape is related to the decrease in calcium content.
Table 4 showed the pectin contents in scape at the end of vase life. WSP contents were lower overall in the occurrence of scape bending and significant difference was found. The high WSP contents were observed in the S1 and S2 sections of scape in both of two types of ornamental value loss. By the way, the WIP contents were overall low in scape bending occurrence and significance was recognized. Especially the S1 section of the bending scape showed the lowest WIP content (1.24 μg·mg-1). Total pectin contents were low in scape bending type, but there was no significant difference in scape sections. Differences of total pectin contents in S1 and S2 section of scape were 1.66 μg·mg-1 and 1.32 μg·mg-1 respectively, which were more difference when compared to the lower part of the scape. The similar results were found in peach that contents of total pectin and WIP were decreased while WSP increased during maturation and storage (Kim et al. 1992). The ratio of the water-insoluble pectin divided by the water-soluble pectin (WIP/WSP) indicated that the lower value, the more aged cell wall (Manganaris et al. 2006).
In bent scape, WIP/WSP ratio of upper two sections of the scape, S1 and S2 sections, were 1.07 and 1.29 respectively, while in scape that did not show bending, same sections of scapes showed WIP/WSP ratio of 1.30 and 1.39 respectively. However, no statistically significant difference was found between bent and unbent scape in S1 and S2 sections. Regardless of occurrence of scape bending, WIP/WSP ratio of S1 and S2 sections of the scape were significantly lower compared to that of lower sections. The content of alcohol insoluble materials and cell walls decreases during ripening and storage of fruit, and the polysaccharide constituting cell walls is degraded by the action of cell wall degrading enzymes and becomes low molecular weight, and insoluble materials decrease while soluble materials increase (Shewfelt 1965). Pectin, a major constituent of middle lamella, is degraded by polygalacturonase and polyuronide is liberated during maturation and storage of pectin, resulting in increased soluble pectin and decreased insoluble pectin (Knee et al. 1977). In cut carnation, high level of insoluble pectins in petal cell walls correspond to long vase life (Jona et al. 1980), WSP contents in petal increased during development and senescence of flower (de Vetten and Huber 1990).
