The Vase Life of Cut Gerbera Flowers is Extended by Combined Treatment with Gibberellin A₃ and Calcium Chloride

Abstract

Treatment with calcium chloride (CaCl₂) is known to suppress the occurrence of flower stem bending and extend the vase life of cut gerbera. To clarify whether vase life extension by CaCl₂ is improved by combined treatment with gibberellin A₃ (GA₃), the effect of treatment with 50 mg·L⁻¹ GA₃, 5 g·L⁻¹ CaCl₂ or in combination on the vase life of the cut gerbera ʻMinouʼ was investigated. To inhibit bacterial proliferation, which is known to shorten vase life, an isothiazoline antimicrobial compound was included in the vase solution. Treatment with GA₃ alone delayed the opening of tubular florets and increased the area of unopen florets, but stem elongation which led to stem bending shortened vase life. Treatment with GA₃ in combination with CaCl₂ suppressed the occurrence of stem bending. Combined treatment with GA₃ and CaCl₂ extended the vase life of cut gerbera more than treatment with CaCl₂ alone. To clarify whether GA₃ delays petal senescence, the effect of GA₃ at 10 and 50 mg·L⁻¹ on petal senescence was investigated using shortened stems. GA₃ at both concentrations significantly delayed petal senescence. Combined treatment with GA₃ and CaCl₂ also significantly extended the vase life of the cut gerbera ʻKimseyʼ and ʻSandyʼ. It was concluded that combined treatment with GA₃ and CaCl₂ is a suitable treatment for extending the vase life of cut gerbera.

Introduction

When purchasing cut flowers, many consumers place a high value on their vase life (Imanishi et al., 1992; Mochizuki-Kawai et al., 2012). The vase life of cut gerbera flowers is thought to be short. In a questionnaire survey of general consumers, more than 80% of respondents answered that the vase life of cut gerbera flowers is less than one week and approximately 25% answered that it is less than three days (Tonooka, 2020). However, the vase life of cut gerbera has also been reported to be longer than one week (Jones and Hill, 1993; Ogasawara et al., 2012). Wilting petals and bending flower stems are signs that cut gerbera flowers are losing their ornamental value. Wernett et al. (1996) reported that the vase life is relatively long when the cut flowers lose their ornamental value due to petal wilting, but it is relatively short when they lose their ornamental value due to stem bending. According to the questionnaire survey, 71% of respondents believe that bending flower stems reduce the ornamental value of cut gerbera flowers (Tonooka, 2020). Therefore, the occurrence of flower stem bending is a major issue to consider in terms of the vase life of cut gerbera.

Bacterial proliferation causes impairment in water relations, which shortens the vase life of cut gerbera (Tonooka et al., 2019; van Doorn and de Witte, 1994). The addition of bacteria to vase water promotes flower stem bending and reduces the vase life of cut gerbera (van Doorn and de Witte, 1994). Antimicrobial compounds inhibit bacterial proliferation in vase water, resulting in the suppression of flower stem bending and the extension of vase life (Tonooka et al., 2019; van Doorn and de Witte, 1994; van Meeteren, 1978). These findings suggest that bacterial proliferation reduces the vase life of cut gerbera.

It has been reported that covering cut gerbera with a sleeve suppresses transpiration and extends their vase life (Perik et al., 2012). Gerbera flowers are harvested without leaves, but stomata were found to be distributed in ray petals and flower stems (Huang et al., 2018). These findings suggest that transpiration from these tissues may shorten the vase life of cut gerbera.

Calcium is known to crosslink pectin and enhance cell wall strength (Thor, 2019; Wyn Jones and Lunt, 1967). In addition, calcium inhibits stomatal opening (Ruiz et al., 1993), and suppresses transpiration in chrysanthemum (van Meeteren et al., 1999). In cut gerbera flowers, spraying, dipping, or injecting with calcium chloride (CaCl₂) solution suppresses the occurrence of flower stem bending and extends vase life (Gerasopoulos and Chebli, 1999). Pulse and continuous treatments with CaCl₂ extend the vase life of cut gerbera (Geshnizjany et al., 2014; Perik et al., 2014).

Phytohormone gibberellin (GA) has various functions, including cell expansion and the promotion of seed germination and flowering (Hedden and Sponsel, 2015). Treatment with GA₃ delays leaf yellowing in cut Alstroemeria (Hicklenton, 1991), lily (Han, 1995), and Narcissus (Ichimura and Goto, 2000). Exogenous GA₃ promotes petal growth in rose (Goszczynska et al., 1990; Sabehat and Zieslin, 1995) and morning glory (Raab and Koning, 1987) and flower opening of statice (Steinitz and Cohen, 1982). Treatment with GA₃ extends the vase life of cut carnation (Saks et al., 1992) and rose (Goszczynska et al., 1990). Pulse treatment with GA₃ delays flower opening and extends the vase life of cut Allium (Sakamoto and Doi, 2007). Emongor (2004) reported that continuous treatment with GA₃ is effective in extending the vase life of cut gerbera without stem bending.

In the present study, we investigated the effect of continuous treatment with GA₃, CaCl₂, and the combination of these treatments, on the growth of petals, stem elongation, and vase life of cut gerbera flowers. To avoid the effects of bacterial proliferation, which shortens the vase life of cut gerbera, an antimicrobial compound was included in the vase solution.

Materials and Methods

Plant materials

Gerbera (Gerbera jamesonii Bolus ex Hook. F.) ‘Kimsey’, ‘Minou’, ‘Pinta’, and ‘Sandy’ were grown in a soilless culture system in a greenhouse at the Shizuoka Prefectural Agricultural and Forestry Research Institute under natural day light conditions as described in Umeda and Tonooka (2020). Ventilation or heating was set to begin at 25 and 15°C, respectively. Flowers were harvested when the most outer tubular flowers had opened. After harvest, flowers were not supplied with water and were used in the following experiments.

Chemical treatment and evaluation of vase life

Unless otherwise stated, flowers were cut to a length of 40 cm and individually placed in test tubes (diameter 40 mm, length 130 mm) containing 100 mL of test solution. The test solution contained 0.25 mL·L⁻¹ isothiazolinone antimicrobial compound, CMIT/MIT (Kathon CG, Rohm and Haas Japan, Tokyo, Japan) containing 5.7 mg·L⁻¹ 5-chloro-2-methyl-4-isothiazolin-3-one and 2 mg·L⁻¹ 2-methyl-4-isothiazolin-3-one as active ingredients. Each solution contained 0.25 mL·L⁻¹ CMIT/MIT with or without 50 mg·L⁻¹ GA₃ (GA3; Tokyo Kasei, Tokyo, Japan) and with or without 2 g·L⁻¹ CaCl₂. CaCl₂ concentration was determined based on previous published results (Tonooka et al., 2023) and the concentration of GA₃ was determined based on the results of preliminary experiments.

To evaluate vase life, nine flowers were used per treatment. The cut flowers were placed in test tubes and kept at 23°C with 70% relative humidity in a 12 h light period (6:00–18:00) with PPFD set to 10 μmol·m⁻²·s⁻¹. Vase life was determined from the start of treatment to the time when one of the following symptoms was observed: bending of the flower stem exceeded 90° (stem bending), abscission of one ray petal (abscission), breakage just below the flower head (neck breaking), or wilting of the petals (wilting).

To investigate the effect of GA₃ concentrations, flowers were cut to a length of 10 cm and individually placed in test tubes containing 0.25 mL·L⁻¹ CMIT/MIT in combination with 0 (control), 10, and 50 mg·L⁻¹ GA₃ (Tokyo Kasei, Tokyo, Japan). To evaluate vase life, eight flowers were used per treatment.

Time to tubular floret opening and relative area of unopened tubular florets

The time required for tubular floret opening was the number of days from the start of treatment until all tubular florets bloomed. The diameter of the unopened tubular florets was measured at the beginning of treatment and every two days thereafter. The unopened tubular floret area was calculated by multiplying the square of the radius by π. The relative area of unopened tubular florets was calculated as the ratio of the unopened tubular floret area at the start of treatment.

Measurement of fresh weight, water uptake, transpiration, and elongation of flower stems

The fresh weight of cut flowers was measured at the start of treatment and every two days thereafter. The relative fresh weight was expressed as the percentage of fresh weight to initial fresh weight. The amount of water uptake was measured every two days and corrected by subtracting the weight of the water evaporated from a test tube without any cut flowers. The amount of transpiration was calculated by subtracting the increase in fresh weight from the amount of water uptake. The rate of water uptake and transpiration was calculated by dividing the fresh weight of flowers at the start of treatment. The length of cut stems was measured at the start of treatment and every two days thereafter. Flower stem elongation was calculated by subtracting the flower stem length at the start of treatment.

Measurement of petal length and width

Petal length and width were measured non-destructively at the start of treatment and every two days thereafter. The relative petal length or width was expressed as the percentage of petal length or width to initial petal length or width, respectively.

Statistical analysis

The Studentʼs t-test, Tukey-Kramer’s multiple range test, and two-way ANOVA were conducted using the BellCurve for Excel software (Social Survey Research Information, Tokyo, Japan).

Results

Effect of GA₃ and CaCl₂ on the vase life of the cut gerbera ʻMinouʼ

Irrespective of CaCl₂ treatment, the time it took for tubular florets to open was longer in GA₃-treated flowers than in GA₃-untreated flowers (Table 1). In the control and CaCl₂ treated flowers, the relative area of unopened tubular florets was almost constant during the first day, and decreased thereafter (Fig. 1A). In contrast, the relative area of unopened tubular florets in GA₃ or GA₃ and CaCl₂-treated flowers increased during the first two days, and decreased thereafter (Figs. 1A and 2).

Table 1

Effect of treatment with 50 mg·L⁻¹ GA₃ and 5 g·L⁻¹ CaCl₂ on time to complete tubular floret opening, vase life, and ornamental value loss symptoms in the cut gerbera ‘Minou’.

Fig. 1

Effect of treatment with 50 mg·L⁻¹ GA₃, 5 g·L⁻¹ CaCl₂ and in combination on the relative area of unopened tubular florets (A), stem elongation (B), relative fresh weight (C), water uptake (D), and transpiration (E) of cut gerbera ‘Minou’ flowers. Values are means of nine replicates ± SE. Different letters at each time point indicate significant differences (P < 0.05) using Tukey-Kramer’s multiple range test.

Fig. 2

Tubular florets of cut gerbera ‘Minou’ five days after the start of treatment. A: Control, B: 5 g·L⁻¹ CaCl₂, C: 50 mg·L⁻¹ GA₃, D: 50 mg·L⁻¹ GA₃ and 5 g·L⁻¹ CaCl₂. Scale bars represent 5 mm.

Length of flower stems in the control increased during vase life (Fig. 1B). Elongation of flower stems was markedly suppressed by CaCl₂ treatment, but was markedly promoted by GA₃ treatment.

In the control and GA₃-treated flowers, the relative fresh weight of flowers increased for the first four days and decreased thereafter. In contrast, in flowers treated with CaCl₂ or GA₃ and CaCl₂, the relative fresh weight of flowers increased for the first eight days and was almost constant thereafter (Fig. 1C). Irrespective of treatments, water uptake and transpiration decreased during the first four or six days, and were relatively low thereafter (Fig. 1D, E). Treatment with GA₃ and CaCl₂ promoted decreases in water uptake and transpiration. The decreases in water uptake and transpiration were suppressed by GA₃ treatment.

GA₃ treatment caused stem bending and significantly shortened vase life (Table 1; Fig. 3). CaCl₂ treatment did not significantly extend vase life, but combined treatment with GA₃ and CaCl₂ significantly extended it.

Fig. 3

Cut flowers of the gerbera ‘Minou’ treated with GA₃, CaCl₂, and their combination. Upper panel: control, middle upper panel: 50 mg·L⁻¹ GA₃, middle lower panel: 5 g·L⁻¹ CaCl₂, lower panel: 50 mg·L⁻¹ GA₃ and 5 g·L⁻¹ CaCl₂. Left panel: 12 days after start of treatment, right panel: 18 days after start of treatment.

Effect of GA₃ concentrations on the vase life of the cut gerbera ʻMinouʼ

To clarify whether GA₃ is effective in extending vase life, the effect of GA₃ concentrations on the vase life of gerbera using cut flowers with shortened stems (10 cm) was investigated.

GA₃ treatments increased the relative area of unopened tubular florets, and 50 mg·L⁻¹ GA₃ was more effective than 10 mg·L⁻¹ GA₃ (Fig. 4A). Irrespective of concentration, GA₃ treatment markedly promoted stem elongation (Fig. 4B). However, stem bending was not caused by GA₃ treatments (Table 2).

Fig. 4

Effect of GA₃ concentrations on the relative area of unopened tubular florets (A), stem elongation (B), and relative fresh weight (C) of cut gerbera ‘Minou’ flowers. Values are means of nine replicates ± SE. Different letters at each time point indicate significant differences (P < 0.05) using Tukey-Kramer’s multiple range test.

Table 2

Effect of GA₃ concentrations on time to complete tubular floret opening, vase life, and ornamental value loss in the cut gerbera ‘Minou’.

The relative fresh weight of cut flowers in the control increased during the first five days, and decreased thereafter. GA₃ treatment at both concentrations suppressed the decrease in relative fresh weight (Fig. 4C). The vase life of cut flowers was significantly extended by GA₃ at both concentrations (Table 2).

Effect of GA₃ and CaCl₂ on the growth of ray petals

The length of ray petals in the control flowers increased during the first four days, and was almost constant thereafter (Fig. 5A). GA₃ treatment significantly promoted the increase in ray petal length. This effect was suppressed by CaCl₂. In contrast, petal width was not significantly affected by these chemical treatments (Fig. 5B).

Fig. 5

Effect of treatment with 50 mg·L⁻¹ GA₃ and 5 g·L⁻¹ CaCl₂ on relative ligulate length (A) and width (B) of cut gerbera ‘Minou’ flowers. Values are means of nine replicates ± SE. Different letters at each time point indicate significant differences (P < 0.05) using Tukey-Kramer’s multiple range test.

Effect of GA₃ and CaCl₂ on the vase life of three gerbera cultivars

In ‘Kimsey’, the relative area of unopened tubular florets decreased with time, and treatment with GA₃ and CaCl₂ suppressed this decrease (Fig. 6A). The relative area of unopened tubular florets was significantly higher in GA₃ and CaCl₂ than in the control in ‘Pinta’ and ‘Sandy’.

Fig. 6

Effect of treatment with 50 mg·L⁻¹ GA₃ and 5 g·L⁻¹ CaCl₂ on the relative area of unopened tubular florets (A), stem elongation (B), relative fresh weight (C), water uptake (D), and transpiration (E) of the cut gerbera ‘Kimsey’ (left), ‘Pinta’ (center) and ‘Sandy’ (right) flowers. Values are means of six replicates ± SE. ** and * indicate significant differences at P < 0.01 and P < 0.05, respectively, by t-test.

In ‘Kimsey’ and ‘Sandy’, the stem length of the control flowers gradually increased with time, and GA₃ and CaCl₂ slightly affected stem length (Fig. 6B). In ‘Pinta’, the stem length of the control flowers markedly increased. In contrast, treatment with GA₃ and CaCl₂ suppressed stem elongation.

For the three cultivars, the relative fresh weight of flowers in the control increased during the first day and decreased thereafter (Fig. 6C). In contrast, the relative fresh weight of flowers treated with GA₃ and CaCl₂ continued to increase over 12 days. In the three cultivars, GA₃ and CaCl₂ treatment slightly affected water uptake and transpiration of cut flowers (Fig. 6D, E). In ‘Kimsey’ and ‘Sandy’, the vase life of cut flowers was significantly extended by GA₃ and CaCl₂ treatment (Table 3).

Table 3

Effect of treatment with 50 mg·L⁻¹ GA₃ and 5 g·L⁻¹ CaCl₂ on time to complete tubular floret opening, vase life, and ornamental value loss in the cut gerbera ‘Kimsey’, ‘Pinta’, and ‘Sandy’.

Discussion

In a preliminary experiment, we found that treatment with GA₃ delayed the opening of tubular florets, but promoted stem bending due to stem elongation, which shortens vase life. In contrast, it has been reported that treatment with CaCl₂ suppresses the occurrence of stem bending and extends the vase life of cut gerbera (Geshnizjany et al., 2014; Perik et al., 2014). In the present study, we investigated the effect of combined treatment with GA₃ and CaCl₂ on stem bending, opening of tubular florets, and the vase life of cut gerbera. Because bacterial proliferation promotes stem bending and shortens the vase life of cut gerbera (Tonooka et al., 2019), two antimicrobial compounds, CMIT/MIT, were added to the vase solution.

The bending of cut gerbera flowers occurs at a position approximately 10 cm below the flower head (Tonooka et al., 2023). Treatment with GA₃ alone promoted stem elongation of cut gerbera, resulting in stem bending (Figs. 1 and 3). In contrast, stem bending was not observed in cut gerbera with shortened length. These results suggest that stem bending is caused by the promotion of stem elongation. Similarly, promotion of stem elongation by GA₃ treatment has been reported in cut tulip (Okubo and Uemoto, 1985; van Doorn et al., 2011). However, Emongor (2004) reported that continuous treatment with GA₃ did not cause stem bending, which differed from our results. This difference may be attributable to the GA₃ concentrations because GA₃ concentrations in the study of Emongor (2004) were much lower than in our study. In addition, this difference may be attributable to differences in cultivars.

Treatment with CaCl₂ alone and combined treatment with GA₃ and CaCl₂ suppressed stem elongation and stem bending (Figs. 1 and 3). CaCl₂ is known to induce stomatal closure and suppress transpiration (Ruiz et al., 1993; van Meeteren et al., 1999). In our study, water uptake was markedly decreased by CaCl₂ treatment (Fig. 1). The rate of water uptake depends on the transpirational pull, temperature and solution composition (van Doorn, 1997). Therefore, the suppression of water uptake is likely to be due to the inhibition of transpiration caused by CaCl₂. For cell expansion, water uptake is necessary. Water uptake is necessary for the cell expansion associated with stem elongation (Chen et al., 1999; Litvin et al., 2016). Therefore, we propose that the inhibition of stem elongation by CaCl₂ is possibly due to the suppression of water uptake, which is caused by the suppression of transpiration.

Treatment with CaCl₂ suppressed flower stem bending and extended the vase life of cut ‘Minou’ flowers (Table 1). In this cultivar, CaCl₂ treatment suppressed transpiration. CaCl₂ treatment has been reported to suppress transpiration from leaves (van Meeteren et al., 1999). Calcium is also known to increase the strength of the cell wall (Wyn Jones and Lunt, 1967). Tonooka et al. (2023) reported that the suppression of flower stem bending with CaCl₂ treatment can be attributed to suppression of transpiration and an increase in the maximum breaking strength.

GA₃ treatment promoted an increase in the length of ray petals, but did not increase the width (Fig. 5). Similarly, Zhang et al. (2012) reported that exogenous GA₃ promoted the growth of inflorescence ray petals using an in vitro culture. The increase in ray petals was shown to be dependent on cell expansion (Zhang et al., 2012). These findings suggest that the promotion of petal growth by GA₃ is likely to be dependent on cell expansion.

GA₃ treatment delayed the senescence of ray petals (Table 2). In general, the onset of visible petal senescence is observed after the termination of petal growth in flowers, including rose (Ichimura et al., 2006), carnation (Fukai et al., 2007), and Delphinium (Ichimura et al., 2000). Therefore, the delay in petal senescence may be due to the promotion of cell expansion. This explanation is supported by findings that treatments with sugars combined with antimicrobial compounds promoted the expansion of petal cells and extended the vase life of cut rose (Norikoshi et al., 2016) and carnation (Fukai et al., 2007).

It has been reported that exogenous GA₃ suppressed ethylene production and extended the vase life of cut carnation (Saks and van Staden, 1993; Saks et al., 1992). Similarly, exogenous GA₃ significantly extended the vase life of cut Narcissus (Ichimura and Goto, 2000), which is sensitive to ethylene to some extent (Hunter et al., 2004). Gerbera flowers are slightly sensitive to ethylene (Woltering and van Doorn, 1988). Therefore, the delay in petal senescence caused by GA₃ may be involved in ethylene production or its action.

Gibberellins are known to be involved in floral development in plants (Mutasa-Gӧttgens and Hedden, 2009). Exogenous GA₃ promotes floral development in many plant species, including petunia (Weiss and Halevy, 1989) and Japanese radish (Nishijima, 2003). In cut gerbera, an increase in the relative area of unopened tubular florets was accompanied by an increase in the number of visible tubular florets (Figs. 1 and 2), suggesting that exogenous GA₃ promotes the development of tubular florets. Also, GA₃ treatment delayed the opening of tubular florets (Fig. 1). Therefore, the freshness of cut gerbera appears to be maintained by exogenous GA₃.

It has been reported that bacterial proliferation shortens the vase life of cut gerbera (Tonooka et al., 2019; van Doorn and de Wiite, 1994). To confirm the effect of GA₃ and CaCl₂ on vase life clearly, CMIT/MIT solution was used as the control. In our study, continuous treatment with GA₃ and CaCl₂ significantly extended the vase life of three out of four cut gerbera cultivars (Tables 1 and 3), indicating that this treatment is useful to extend vase life. However, this treatment did not significantly extend the vase life of cut ʻPintaʼ. Tonooka et al. (2023) reported that the vase life of ʻPintaʼ kept in distilled water was 18.1 days, which was the longest among eight gerbera cultivars. Therefore, the vase life of ʻPintaʼ seems to be sufficiently long without chemical treatment.

Our study demonstrated that continuous treatment with GA₃ and CaCl₂ extended the vase life of cut gerbera (Tables 1 and 3). Many cut flowers, including carnation and Delphinium, are treated with preservatives before shipping to extend vase life (Ichimura et al., 2011; Kato et al., 2022). The time available for treating cut flowers with preservatives before shipping is limited. Therefore, it is desirable that the time required for GA₃ and CaCl₂ treatment be as short as possible. To clarify whether pulse treatment with GA₃ and CaCl₂ is effective in extending the vase life of cut gerbera, further study is necessary.

Continuous treatment with GA₃ in cut gerbera caused stem bending due to marked elongation, which shortened vase life. However, GA₃ treatment delayed the opening of tubular florets and delayed the senescence of ray petals using shortened stems. Stem elongation caused by GA₃ treatment was suppressed by the combined treatment with CaCl₂. Thus, continuous treatment with GA₃ and CaCl₂ was effective in extending the vase life of cut gerbera.

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