EFFECT OF GIBBERELLIC ACID ON THE QUALITY OF CUT FLOWERS OF ZANTEDESCHIA ELLIOTTIANA (W. WATS.) ENGL.

Beata Janowska, Marek Jerzy

ABSTRACT

Two experiments were carried out to determine the effect of gibberellic acid on the longevity of cut flowers of two Zantedeschia elliottiana (W. Wats.) Engl. cultivars: 'Black Magic' and 'Florex Gold'. The flowers were conditioned for 2, 4 and 20 hours in water solutions of 8-hydroxyquinoline citrate at concentrations of 200 mg l^-1, and then kept in water or gibberellic acid solutions at concentrations of 50 and 100 mg l^-1. Gibberellic acid and 8-hydroxyquinoline citrate had different effects on the quality of cut flowers of Zantedeschia elliottiana cultivars: 'Black Magic' and 'Florex Gold'. Gibberellic acid at concentrations of 50 and 100 mg l^-1 caused an elongation of peduncles of unconditioned inflorescences in 'Black Magic'. A similar response was observed in unconditioned flowers put in water. In cultivar 'Florex Gold', both concentrations of gibberellic acid caused a lengthening of flower peduncles irrespective of the duration of conditi

Key words: Zantedeschia elliottiana, gibberellic acid, cut flowers, quality..

INTRODUCTION

The longevity of cut flowers is usually shorter than that of flowers developing on a plant. Dozens of formulas have been devised in the world for preparations prolonging the postharvest longevity of flowers or improving the quality of bloom. It is impossible, however, to come up with a medium that would have exactly the same effect on all species of ornamental plants, hence individual preparations are employed to extend flower longevity [12]. Common components of media used for this purpose are 8-hydroxyquinoline esters: sulphate and citrate, which have bactericidal and fungicidal properties.

So far few studies have been conducted involving cut flowers of the golden calla lily with colourful spathes. Equally scarce are reports of the quality of cut flowers of this species. Studies of the postharvest longevity of Zantedeschia elliottiana leaves, however, show that gibberellic acid not only extends their longevity, but also improves their postharvest quality [5, 6].

MATERIALS AND METHODS

In 2001 and 2003, experiments were carried out in the Department of Ornamental Plants of the Agricultural University in Poznań to investigate the effect of gibberellic acid on the longevity of cut flowers of two cultivars of the golden calla lily (Zantedeschia elliottiana /W. Wats./ Engl.): 'Black Magic' and 'Florex Gold'.

The experiments were conducted at a temperature of 18-20°C and a 12-h photoperiod, employing luminescence light with a quantum irradiance intensity of 25 μmol m²s^-1. The relative air humidity was maintained at 70%.

Unconditioned flowers were placed in water or gibberellic acid solutions at concentrations of 50 and 100 mg l^-1. The remaining ones were conditioned for 2, 4 and 20 hours in water solutions of 8-hydroxyquinoline citrate at a concentration of 200 mg l^-1. The reaction of the solution was slightly acidic (pH 5.0). After conditioning the flowers were kept in water or gibberellic acid solutions at concentrations of 50 and 100 mg l^-1. Use was made of Gibrescol containing 98% of gibberellic acid (GA₃).

Water was changed every day and gibberellic acid solutions, every three days.

A single experiment consisted of 12 combinations with three replications carried out on 5, 10 and 15 July 2001 and on 5, 12 and 19 June 2003. On each date the longevity of 5 flowers was tested. Each treatment included a total of 15 flowers.

The postharvest quality of the flowers was determined as expressed by bloom weight, length of peduncles, and length and width of spathes. Also determined were the losses of flower weight, length of flower peduncles, and length and width of spathes. The losses and increments were given in per cent. The loss of ornamental qualities was set at that point in time when one third of the spathe had dried and/or wilted.

RESULTS

Flower peduncles lost weight as the experiment proceeded. The biggest weight loss in cultivar 'Black Magic' (28.7%) was recorded in flowers conditioned for 2 hours in a solution of 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 50 mg l^-1. A substantial weight loss was observed when flowers were not conditioned at all, or conditioned for 2 hours in a solution of 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 100 mg l^-1 (losses of 26.2% and 25.3%, respectively). The loss of weight was the lightest (15.8%) when flowers were conditioned for 4 hours in a solution of 8-hydroxyquinoline citrate and kept in water. In the remaining combinations, flowers lost from 19.0% to 22.4% of their weight (Table 1).

In cultivar 'Florex Gold' the biggest weight loss (34.3%) was observed in flowers which were not conditioned but merely kept in a solution of gibberellic acid at a concentration of 100 mg l^-1. The lightest loss of weight was recorded in flowers conditioned for 4 hours in a solution of 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 100 mg l^-1 (22.8%), as well as in flowers placed in water after 20 hours' conditioning in a solution of 8-hydroxyquinoline citrate (24.2%). In the remaining combinations, flowers lost from 25.0% to 30.5% of their weight (Table 2).

At the start of the experiment, flower stems of cultivar 'Black Magic' were 51.9 cm to 67.4 cm long. Their length was observed to have changed as the experiment drew to an end. In the case of flowers which were not conditioned but only kept in water or gibberellic acid at concentrations of 50 and 100 mg l^-1, the increment in flower peduncle length was the smallest in those kept in water (2.1%) and the higher in those kept in gibberellic acid (2.7% and 3.8%, respectively). Also flowers conditioned for 2 hours in a solution of 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 100 mg l^-1 had longer peduncles, by 3.4%, at the close of the experiment. In the remaining combinations, flower peduncles became shorter as a result of the advancing sliming of tissue. Loss of length was the most conspicuous in flowers placed in water after 2, 4 and 20 hours conditioning in a solution of 8-hydroxyquinoline citrate. Storing the plants in a solution of gibb erellic acid substantially reduced the adverse effect of 8-hydroxyquinoline citrate. Keeping the conditioned plants in a solution of gibberellic acid reduced flower peduncle shortening to 0.5% after 2 hours conditioning and to 1.3% after 20 hours conditioning. In the combination where gibberellic acid at a concentration of 100 mg l^-1 was used for storing flowers after 4 and 20 hours conditioning in 8-hydroxyquinoline citrate, the flower peduncles became shorter by 2.2% and 2.1%, respectively (Table 3).

In cultivar 'Florex Gold' the flower peduncles lengthened during the experiment. The smallest increment (0.8%) was recorded in the combination where flowers were placed in water after 4 hours' conditioning. The biggest increments of stems (2.2% and 2%) on finishing the experiment were observed in plants conditioned for 4 and 20 hours in a solution of 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 50 mg l^-1 (Table 4).

The spathes of 'Black Magic' tended to dry as a result of the advancing process of senescence, hence by the end of the experiment both their length and width had lessened (Tables 5 and 7). The lowest proportion of spathe length reduction was observed in flowers conditioned for 4 hours in a solution of 8-hydroxyquinoline citrate and kept in water as well as in a solution of gibberellic acid at a concentration of 100 mg l^-1 (about 3.0%). A similar response was observed in flowers of this variety placed in water after 20 hours' conditioning. In the remaining combinations, the length of the spathe was reduced a bit more (Table 5).

The biggest losses in spathe width in this variety, 50.0% and 54.2%, were recorded in flowers which were not conditioned at all, or conditioned for 2 hours in a solution of 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 50 mg l^-1. In the remaining combinations, by the end of the experiment flowers had spathes 26.9%-36.4% narrower than when it began (Table 7).

Depending on the combination, the spathes of cultivar 'Florex Gold' lengthened a bit. The biggest increment was observed in flowers which were conditioned for 20 hours and kept in gibberellic acid at a concentration of 50 mg l^-1. Only in two combinations, the control and the one where flowers were conditioned for 4 hours in 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 50 mg l^-1, was spathe length the same at the start and close of the experiment. A slight drying of spathe tips (1%) was observed in the combination where flowers were conditioned for 2 hours in 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 100 mg l^-1, and the one where they were conditioned for 4 hours in 8-hydroxyquinoline citrate and kept in water (Table 6). In this variety, during senescence the spathes tended to shrink and turn green. The shrinking was the least conspicuous in the combination where uncond itioned flowers were placed in a gibberellic acid solution at a concentration of 50 mg l^-1. In the remaining combinations, by the end of the experiment flowers had spathes 16.7%-34.1% narrower than when it began (Table 8).

DISCUSSION

One of the symptoms of senescence of cut flowers is a decrease in their fresh weight caused by a negative water balance due to transpiration exceeding water uptake [1, 7, 10, 13, 15]. The cutting disrupts the water column in vascular bundles, which in turn leads to the sucking in of air bubbles which block capillaries and obstruct the free flow of water. Also bacteria and fungi in the water can be the cause of capillary blocking and hindered water flow. That is why bactericidal and fungicidal preparations are used to prevent this development.

In the experiment reported, a solutions of 8-hydroxyquinoline citrate was used to condition Zantedeschia elliottiana flowers. Flowers of the 'Black Magic' cultivar lost most weight when conditioned for 2 hours in an 8-hydroxyquinoline citrate solution and kept in gibberellic acid at a concentration of 50 mg l^-1. They suffered the smallest loss when placed in water after 4 hours conditioning. In 'Florex Gold', the biggest loss of weight was observed in flowers which were not conditioned but only kept in a solution of gibberellic acid at a concentration of 100 mg l^-1. The smallest loss of weight in this variety was recorded in flowers conditioned for 4 hours in a solution of 8-hydroxyquinoline citrate and kept in gibberellic acid at a concentration of 100 mg l^-1, as well as in flowers placed in water after 20 hours conditioning in a solution of 8-hydroxyquinoline citrate.

The gibberellic acid used in the experiment at concentrations of 50 and 100 mg l^-1 brought about a lengthening of peduncles in unconditioned flowers of cv. 'Black Magic' and of peduncles and spathes in cultivar 'Florex Gold'.

In the studies by Goszczyńska et al. [4] and Łukaszewska and Kokosa [12], the addition of gibberellic acid to a medium containing sugar not only extended the vase-life of Narcissus, but also lengthened the cups in 'Trumpet' cultivars. Studies on Tulipa show that the best medium is one including 8-hydroxyquinoline citrate, gibberellic acid and Ethrel, which prevents excessive growth of stems and excessive opening of the bud. Gibberellic acid improves the opening of tulip buds, thus making them more ornamental [8, 12, 14]. In Nerine, gibberellic acid applied in a medium containing saccharose and 8-hydroxyquinoline citrate improves the quality of inflorescences because it brings about an elongation of peduncles and petals and a flatter arrangement of flowers in the umbel [9, 12]. No such effect has been observed in Hippeastrum hybridum and Hippeastrum x chmielii, but gibberellic acid significantly extends the post-harvest longevity of their flowers [11]. Acco rding to Tjia and Funnell [16], flowering stems of Zantedeschia aethiopica and Z. elliottiana placed in pure water tend to split. To prevent this, they suggest adding sugar and 8-hydroxyquinoline citrate to the medium. However, even such a solution does not lengthen the vase-life of flowers. According to them, calla lilies should be conditioned in this solution for one night at a temperature of 5-10°C. The authors state that the post-harvest longevity of Zantedeschia aethiopica is limited to 6-7 days, while in Z. elliottiana the spathes start to turn green after as few as 7-8 days, which decreases their decorativeness. Funnell and Downs [3] count Zantedeschia hybrids among species insensitive to ethylene. Funnell [2] as well as Łukaszewska and Kokosa [12] emphasise that in Zantedeschia aethiopica sugar added to the medium leads to rapid desiccation of tissue and spathe necrosis. In the present study stem splitting was not observed, and spathe greening was only observe d in 'Florex Gold' irrespective of the duration of conditioning and the concentration of gibberellic acid. However, stems tended to become slimy in the 'Black Magic' cultivar conditioned in an 8-hydroxyquinoline citrate solution. This development was counteracted by storing the flowers in gibberellic acid solutions.

CONCLUSIONS

1. Gibberellic acid and 8-hydroxyquinoline citrate had different effects on the quality of cut flowers of Zantedeschia elliottiana cultivars: 'Black Magic' and 'Florex Gold'.

2. Gibberellic acid at concentrations of 50 and 100 mg l^-1 caused an elongation of peduncles of unconditioned inflorescences in 'Black Magic'. A similar response was observed in unconditioned flowers put in water. In cultivar 'Florex Gold', both concentrations of gibberellic acid caused a lengthening of flower peduncles irrespective of the duration of conditioning.

3. The conditioning of 'Black Magic' flowers in 8-hydroxyquinoline citrate solutions was detrimental to their quality irrespective of the duration of the treatment.

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