The Effect of 8-Hydroxyquinoline Sulphate and Gibberellic Acid on Postharvest Viola odorata L. Leaf Longevity

Abstract

The aim of the study was to evaluate the postharvest longevity of cut leaves of Viola odorata and determine their usefulness as a florist green. The research also involved the study of the influence of chemical compounds used as plant preservatives on the longevity of leaves of V. odorata. The leaf stalks of V. odorata were soaked in water or conditioned in a 200 mg·dm⁻³ solution of 8–hydroxyquinoline sulphate, or a 50 or 100 mg·dm⁻³ solution of gibberellic acid. After one day, the leaves were kept in water or 200 mg·dm⁻³ of 8–hydroxyquinoline sulphate. The leaves of V. odorata had a longevity of about 31 days in water. Both the conditioning in gibberellic acid and 8–hydroxyquinoline sulphate and the maintenance in 8–hydroxyquinoline sulphate reduced the vase life of cut V. odorata leaves. The application of conditioners resulted in a significantly greater reduction of the leaf mass. The Soil Plant Analysis Development value of the leaves was best affected by conditioning them in 100 mg·dm⁻³ gibberellic acid followed by keeping them in water. Cut leaves of V. odorata with water treatment may be used as a florist green.

1. Introduction

The development of the flower industry has resulted in an increased demand for new plant materials that could be used as decoration in flower arrangements. The cultivation of warmer-climate greenery in the temperate climate conditions is often unprofitable or even impossible. Therefore, such florist greens are replaced by temperate-climate plants grown in greenhouses and in open fields.

Viola odorata L. is a perennial indigenous to the temperate climate zone. Fragrant violets or white flowers develop in May. Their postharvest longevity is 3–7 days [1]. The leaves are small and not very showy at the beginning of the vegetation period, and could reach a diameter of up to 8 cm. They are ovate with serrated edges [2]. The mature leaf stalks of V. odorata look very attractive and therefore seem suitable for floral arrangements. However, the available literature provides no information on the postharvest longevity of V. odorata leaves and the methods for extending it.

To fill this information gap, this study assessed the effect of gibberellic acid (GA₃) and 8-hydroxyquinoline sulphate (8HQS), the most commonly used plant conditioners, on the postharvest longevity of the cut leaves of V. odorata as potential florist greenery. GA₃ improves postharvest longevity by, among other things, postponing the yellowing of leaves [3,4,5]. 8HQS is an antimicrobial agent used in the floral industry to increase the vase life of cut flowers [6,7].

2. Materials and Methods

2.1. Experimental Materials and Design

The experiment was conducted in July and August of two consecutive years in a growth chamber of the Department of Ornamental Plants, Dendrology and Pomology at the Poznań University of Life Sciences, Poznań, Poland. Fully developed leaves of V. odorata were harvested from an opened field culture run in the Department’s teaching garden. Leaf stalks were 19–20 cm long, while leaf blades were 7–8 cm in diameter. Each leaf was weighed.

The harvested leaves were soaked in water or conditioned in aqueous solutions of the following chemical agents: GA₃ at a concentration of 50 or 100 mg·dm⁻³ (Chmes, Poznań, Poland) and 8HQS (Acros Organics, New Jersey, USA) at a concentration of 200 mg·dm⁻³. During soaking or conditioning, the leaf stalks were immersed approximately 4 cm deep in the liquid for 24 h. After soaking in water and conditioning, one half of the leaves was kept in water, and the other half was kept in a 200 mg·dm⁻³ aqueous solution of 8HQS. One of the combinations was to soak the leaves in water and, after 24 h, treat them with 8HQS at a concentration of 200 mg·dm⁻³. The vase water and the 8HQS solution were replaced every three days.

The experiment consisted of eight treatment combinations with nine leaves. One leaf constituted one replication.

The experiment was run in a chamber at a temperature of 18 ± 1 °C and artificial white lighting of 10 h/d, with a quantum irradiance of 25 μmol·m⁻²·s⁻¹.

2.2. Measurements

The vase life of leaves was measured in days. The leaves were removed from the experiment when yellow or brown spots as well as curling or drying leaf blade margins were observed on them. Each leaf was weighed before removal. A Soil Plant Analysis Development (SPAD) meter was used to indicate the relative chlorophyll content in the center part of the leaves. The SPAD chlorophyll index was recorded every four days. The first measurement was conducted at the onset of the experiment, and the last one on the day the leaf was removed from the experiment. These measurements were taken using an N–tester (Yara-Poland, Szczecin, Poland). After the experiment, the percentage change in the mass of fresh matter and the SPAD index was calculated in relation to the initial mass and initial SPAD value. The postharvest longevity of the leaves varied, so three combinations were compared in terms of the SPAD index during 28 days (water + water, 50 mg·dm⁻³ GA₃ + water, 100 mg·dm⁻³ GA₃ + water). The SPAD index was also measured for all combinations during the first 16 days of the experiment.

2.3. Statistical Analysis

The results were subjected to a two-way analysis (conditioning × vase solution) of variance using Statistica (software version 13.3, StatSoft, Kraków, Poland), while means were grouped using the Duncan test at the significance level p = 0.05.

3. Results and Discussion

The longevity of cut leaves of Viola odorata kept in water was 31 days (

Table 1. Effect of postharvest treatment on longevity of Viola odorata leaves (days).

Conditioning	Vase Solution		Mean
	Water	8HQS
Water	31.3 f	17.9 bc	24.6 b
GA3 50 mg·dm−3	29.0 ef	5.8 a	17.4 a
GA3 100 mg·dm−3	24.4 de	12.9 b	18.7 a
8HQS 200 mg·dm−3	20.0 cd	17.4 bc	18.7 a
Mean	26.2 b	13.5 a

Mean values marked with the same letter in the columns do not differ at the significance level p = 0.05 according to the Duncan’s test.

). Sacalis [1] reported that leaves of Rumohra adiantiformis had a vase life of 3–4 weeks. The vase life of Viola leaves is a satisfactory value. In turn, the longevity of Hedera helix leaves, being of a comparable size, is 2–4 weeks [1].

The postharvest longevity of V. odorata leaves depended on the chemical agents applied in the conditioning and storage stage. Leaves conditioned in the 50 mg·dm⁻³ gibberellic acid solution and then kept in water had the same statistical longevity as the control combination (leaves immersed in water in both phases). However, the use of the 100 mg·dm⁻³ gibberellic acid solution as a conditioner shortened the longevity of the leaves. According to other studies, florist greens vary in their response to chemical agents, depending on the plant species. In an experiment by Henschke et al. [8], gibberellic acid (100 mg·dm⁻³) reduced the longevity of cut shoots of Glyceria maxima ‘Variegata’ and Spartina pectinata ‘Aureomarginata’, but such a treatment increased the longevity of shoots of Miscanthus sinensis ‘Zebrinus’. The lack of effect of GA₃ conditioning on the extension of the vase life may be the result of the leaf blade’s capacity to synthesize this growth regulator in the leaves.

GA₃ plays an important role in creating the water balance of cells [9]. In Zantedeschia elliottiana, irrespective of its cultivar, the postharvest longevity was extended as a result of gibberellic acid conditioning [10]. A positive effect of gibberellic acid was also reported by Isapareh et al. [11], Abshahi et al. [12], Al–Hasnawi et al. [9] and Aziz et al. [5] when investigating the application of this compound to, respectively, Alstroemeria ‘Bridal’ (50, 100 mg·dm⁻³ GA₃), Cycas (5 mg·dm⁻³ GA₃), Gladiolus hybridus (50 mg·dm⁻³ GA₃) and lily (100 mg·dm⁻³ GA₃). The findings of the above studies also suggest that the effect of GA₃ depends on the plant species.

The leaves of V. odorata also had a reduced longevity after being conditioned in 8HQS. Opposite results were found by Ulczycka–Walorska and Krzymińska [13] and by Mirjalili et al. [7], who investigated the longevity of Waldsteinia geoides (200 mg·dm⁻³ 8HQS) and Rosa ‘Angelina’ (200 mg·dm⁻³ 8HQS), respectively. Treatment with 8HQS (200 mg·dm⁻³) did not extend the longevity of ornamental grasses [8].

8HQS exhibits bactericidal and fungicidal activity [8]. Keeping V. odorata leaves in 8HQS after conditioning also had an adverse effect on their postharvest longevity. As was reported by Janowska and Jerzy [14], 8HQS (200 mg·dm⁻³) reduced the postharvest longevity of Zantedeschia elliottiana ‘Florex Gold’. In contrast, no effect of 8HQS was observed on the vase life of ‘Black Magic’. According to Hassan and Schmidt [15], the addition of 8HQS might extend the postharvest longevity of Dianthus caryophylus, especially when the solution is supplemented with sucrose (sucrose produces the necessary nutrients for cell growth).

The leaf mass decreased in the course of the experiment (

Table 2. Effect of postharvest treatment on the weight change of Viola odorata leaves (%).

Conditioning	Vase Solution		Mean
	Water	8HQS
Water	−5.9 cd	3.4 f	−1.3 c
GA3 50 mg·dm−3	−10.5 a	−7.5 bc	−9.0 a
GA3 100 mg·dm−3	−7.9 bc	−4.9 d	−6.4 b
8HQS 200 mg·dm−3	−8.9 ab	−2.2 e	−5.5 b
Mean	−8.3 a	−2.8 b

Mean values marked with the same letter in the columns do not differ at the significance level p = 0.05 according to the Duncan’s test.

). The exception was when the leaves were first soaked in water and then kept in 8HQS. The leaf mass percentage loss depended both on the method of conditioning and the liquid in which the cut leaves were kept afterwards. Conditioning in GA₃ and 8HQS increased the percentage loss of the leaf mass. This is in agreement with Bunya–Atichart et al. [16]. According to the authors, conditioning in gibberellic acid reduced the mass loss of Curcuma alismatifolia. However, GA₃ conditioning of Gerbera jamesonii [17] resulted in a mass increase. As for 8HQS, it might have a positive effect on changes in plant mass, as shown by Elhindi [18] and Asrar [19] for Lathyrus odoratus and Antirrhinum majus, respectively.

The analysis of changes in the SPAD values of V. odorata leaves showed that the application of chemical agents influenced this feature (Figure 1). The SPAD values after eight days of the experiment increased when gibberellic acid at a concentration of 100 mg·dm⁻³ was used as a conditioner and the leaves were kept in water afterwards. A positive response to the application of gibberellic acid was also observed in Weigella florida [20] and oriental lily [21]. GA₃ is able to prevent leaf yellowing [22]. The synergic effect can be reached in combination with other chemicals. The leaves of V. odorata conditioned in 50 mg·dm⁻³ GA₃ and later kept in water had lower SPAD values than the leaves in the other two combinations. A positive effect of conditioning the leaves in 100 mg·dm⁻³ GA₃ followed by keeping them in water was also observed by comparing the SPAD values obtained for other combinations during the first 16 days (Figure 2). However, the results were not correlated with postharvest longevity. Gibberellic acid was also found to have no influence on the SPAD values of Mathiola incana [22].

4. Conclusions

• The postharvest longevity of cut leaves of Viola odorata kept in water was approximately 31 days.
• Conditioning cut V. odorata leaves in gibberellic acid applied at a concentration of 50 or 100 mg·dm⁻³ and 8-hydroxyquinoline sulphate at a concentration of 200 mg·dm⁻³ significantly reduced their vase life.
• Keeping cut V. odorata leaves in 8-hydroxyquinoline sulfate after conditioning shortened their postharvest longevity.
• Conditioning cut leaves of V. odorata in gibberellic acid used at a concentration of 50 or 100 mg·dm⁻³ and 8-hydroxyquinoline sulphate at a concentration of 200 mg·dm⁻³ caused an increase in the percentage loss of their mass. Keeping cut leaves of V. odorata in 8-hydroxyquinoline sulphate after conditioning reduced their percentage mass loss.
• The leaf chlorophyll index depended on the interaction of experimental factors. The most advantageous effect on its value was observed for leaves conditioned in gibberellic acid applied at a concentration of 100 mg·dm⁻³ and then kept in water.
• Cut leaves of V. odorata with water treatment may be used as a florist green.