An Alternative Postharvest Handling Strategy for Cut Flowers – Dry Handling after Harvest A.J. Macnisha, A. de Theije and M.S. Reid Department of Plant Sciences University of California Davis, CA 95616 USA
C.-Z. Jiang Crops Pathology & Genetics Research Unit USDA-ARS Davis, CA 95616 USA
Keywords: bruising, hydration, opening, Rosa, solution uptake, vase life Abstract The most traditional first step after harvesting flowers is to place the cut stems into water or a postharvest solution. Although this step is thought to reduce desiccation, and thereby extend postharvest life, there has been no detailed study of this hypothesis. We harvested rose flowers from commercial farms near Bogotá, Colombia and Quito, Ecuador. Flowers were either hydrated as per conventional practice, or not provided with immediate postharvest hydration. They were then processed and transported to Davis, California, following standard commercial practices. Despite substantial loss of water during transport, dry-handled flowers rehydrated fully, and performed at least as well in the vase as flowers handled according to the standard protocol. Our data suggest that the value of immediate hydration of harvested flowers should be carefully examined, not only for roses, but for other important species. INTRODUCTION It is customary to hydrate cut flowers after harvest. This practice can restore the loss in flower turgidity that occurs during dry handling of stems in the greenhouse and help limit water deficit stress associated with subsequent dry shipment (Halevy and Mayak, 1981; van Doorn, 1997). Hydration after harvest also ensures continued growth and development (e.g. petal expansion, flower opening) of cut flowers (Mayak and Halevy, 1971; Evans and Reid, 1988). In addition, hydration provides an opportunity to administer water soluble chemical inhibitors of ethylene action (e.g. silver thiosulfate) and leaf senescence (e.g. cytokinin) to flowers (Reid, 2002). Although immediate postharvest hydration is thought to extend the longevity of flowers by reducing desiccation, there has been no detailed study of this hypothesis. Given the considerable cost of infrastructure and time taken to provide postharvest hydration it seems important to validate this practice. Indeed, it is possible that hydrating some flower species prior to conventional dry shipment may not always be desirable. Hydrating flowers after harvest may increase the risk of introducing bacterial occlusions into stems, either directly from contaminated solutions (Zagory and Reid, 1986; de Witte and van Doorn, 1988) or by continued growth of bacteria in xylem conduits during dry shipment (van Doorn and de Witte, 1991; van Doorn and D’hont, 1994). In the current study, rose flowers were used to test the hypothesis that dry handling of harvested stems would not compromise flower quality and longevity. MATERIALS AND METHODS Plant Material and Hydration Treatments Flowering stems of Rosa hybrida ‘Black Magic’, ‘Charlotte’, ‘Freedom’, ‘Osiana’ and ‘Vendela’ were harvested between 0800 and 1200 from plants in greenhouses in Bogotá, Colombia and Quito, Ecuador. Cut stems were immediately placed into buckets containing a commercial hydration solution (2 ml/L Chrysal Clear Professional 1, Pokona
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Proc. IX th Int’l Symp. on Postharvest Quality of Ornamental Plants Eds.: C.-O. Ottosen et al. Acta Hort. 847, ISHS 2009
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Chrysal) or held dry. Stems were taken to the postharvest building within 1 h. Flowering ends of stems were dipped for 10 seconds in a fungicide solution (1 ml/L Sportak®, Bayer CropScience), graded for uniformity, combined into bunches of 25 stems and re-cut to 60 or 70 cm. Bunched stems were placed back into the hydration solution or kept dry for 24 h at 2°C. Bunches were packed into commercial flower boxes containing temperature dataloggers and shipped from the farms to the University of California in Davis by airplane and refrigerated truck within 8 days. Temperatures during shipment typically varied between 2 and 17°C. Rehydration and General Processing Upon arrival at the Davis laboratory, flower bunches were removed from boxes and inspected for visual quality. Stems were re-cut by trimming about 2.5 cm from their base to remove air emboli. They were then placed into a commercial rehydration solution (10 ml/L Chrysal Clear Professional 2, Pokon-Chrysal) for 24 h at 0°C. Stems were trimmed to 40 cm-length. All except the uppermost three leaves were detached from stems. Twelve stems were randomly sampled from each hydration treatment and placed individually into vases containing a commercial vase solution (10 g/L Chrysal Clear Professional 3, Pokon-Chrysal). Flower stems were maintained at 20°C, 50% relative humidity, and were illuminated with 18 µmol/m2 s-1 of light provided by overhead cool white fluorescent bulbs (12 h/day). Assessments Flower bunches were weighed immediately after harvest, and before and after shipment and rehydration. ‘Vendela’ flowers and vases were also weighed on every second day of vase life to enable calculation of flower weight and solution uptake. The number of petals showing bruising following dry shipment was also determined for ‘Vendela’ flowers. Flower opening and vase life was determined for each cultivar. Flower opening was subjectively assessed every second day using a modified version of the scale described by Kuiper at al. (1996) whereby 1=closed flower with sepals vertically adhered; 2=slightly open flower with sepals beginning to fold down; 3=half open flower; 4=external petals almost horizontal, intermediate petals totally opened and internal petals starting to open; and 5=completely open flower showing reproductive organs. Vase life was judged as the time (days) from placement in vases to the loss of visual appeal (viz. petal wilting, abscission, blueing and disease, flower drooping). RESULTS Changes in Flower Weight during Handling and Shipment Cut ‘Charlotte’ rose flower bunches lost 1.3% weight during the ca. 1 h dry transport from the greenhouse to the postharvest building, while matching bunches that received hydration throughout this period gained 5.0% weight (Table 1). Dry-handled and hydrated ‘Charlotte’ stems then increased in weight by 4.5 and 5.1%, respectively, following the fungicide dip treatment and 24 h dry storage or hydration at 2ºC to depart the farm at 1.9 and 10.1% above harvest weight, respectively (Table 1). Flower bunches lost ca. 5.0% weight during the 8-day dry shipment from Colombia to California. Dryhandled flowers then displayed higher rates of uptake during rehydration as evidenced by a significantly greater increase in weight (Table 1). Nevertheless, the total increase in weight from harvest to the completion of rehydration was significantly lower for dryhandled flowers than for the conventionally hydrated stems. Similar changes in weight were observed for all other tested cultivars (data not shown). Petal Bruising ‘Vendela’ stems that were hydrated after harvest had 2.5 times as many bruised petals per flower as stems that were handled dry at the farm (Fig. 1).
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Flower Opening ‘Vendela’ stems that were hydrated after harvest arrived in California displaying more open flowers that those that were dry-handled (Fig. 2). However, dry-handled ‘Vendela’ flowers opened more rapidly during vase life than stems that were hydrated prior to shipment (Fig. 3). A similar response was observed for ‘Black Magic’ flowers (data not shown). Rates of flower opening during vase life were independent of the farm hydration treatment for ‘Charlotte’, ‘Freedom’ and ‘Osiana’ stems (data not shown). Vase Life Dry-handled ‘Black Magic’ and ‘Osiana’ flowers had a significantly longer vase life (by 3.4 and 2.8 days, respectively) than stems that received hydration at the farm (Table 2). Relative to stems that received the standard hydration treatment, dry handling did not effect the vase life of ‘Charlotte’, ‘Freedom’ and ‘Vendela’ flowers. Changes in Flower Weight and Solution Uptake during Vase Life Dry handling ‘Vendela’ flowers after harvest did not significantly affect changes in the fresh weight of stems during vase life (data not shown). However, the dry-handled stems maintained significantly higher rates of solution uptake during vase life compared to stems that received conventional hydration (Fig. 4). DISCUSSION The findings of our study support the hypothesis that dry handling has no negative impact on the postharvest quality and longevity of cut rose flowers. These results are in contrast to the long-held view that harvested flowers such as rose, chrysanthemum and gerbera are best handled in water under refrigeration before packing and shipping (Halevy and Mayak, 1981). Our data are, however, consistent with reports that dry storage can extend the postharvest life of some flowers (e.g. bud-stage carnation) (Goszczynska and Rudnicki, 1983; Halevy and Mayak, 1981). On the basis of the observed responses, we suggest that the value of immediate hydration of harvested roses and other species intended for storage or long-distance transport should be carefully examined. Dry-handled ‘Vendela’ rose flowers showed less transportation damage (largely petal bruising) on arrival in California (Fig. 1), presumably because of reduced petal turgor, growth and total volume (Mayak and Halevy, 1971; Evans and Reid, 1988; van Doorn, 1997). These results are in agreement with observations that flower development, including senescence, is reduced for dry-stored flowers (Nowak and Rudnicki, 1990). Moreover, the reduction in tissue damage has potential to reduce the development of Botrytis cinerea on petals during shipment and storage (Reid, 2002). Despite losing a substantial amount of water (5.0% weight) during processing and transport, dry-handled flowers were not visibly wilted on arrival (Fig. 2). The weight lost by dry-handled flowers was less than the critical level of desiccation (10-15%) previously found to reduce the longevity of a range of cut rose flower cultivars (Mokhtari and Reid, 1995; Borda et al., unpublished data). Dry-handled flowers rehydrated rapidly after shipment (Table 1) and displayed enhanced rates of solution uptake and flower opening during vase life (Figs. 3 and 4). Presumably dry handling resulted in more favorable water relations during vase life than for flowers hydrated after harvest. Relative to stems that received standard hydration, the significantly higher rates of vase solution uptake by dryhandled flowers may reflect a reduction in the number of bacteria that typically colonize cut flower stems (de Witte and van Doorn, 1988). Bacteria on flower stems and in contaminated postharvest solutions can enter xylem vessels during hydration and proliferate during subsequent dry storage (van Doorn and de Witte, 1991). The resulting bacteria-related stem occlusions can inhibit the opening and longevity of many cut flowers, including rose, in association with low rates of water uptake (van Doorn, 1997). The improved water relations of the dry-handled stems were translated into extended vase life for two (‘Black Magic’, ‘Osiana’) out the five tested cultivars (Table 2). In the remaining cultivars (‘Charlotte’, ‘Freedom’, ‘Vendela’), flowers that were dry 217
handled performed at least as well in the vase as stems handled using the standard protocol. This finding highlights the potential for the practice of dry handling to be extended to a broader range of rose cultivars. Our data are also consistent with observations that long-term transportation of cut flowers in water, whilst maintaining turgidity, is associated with a reduction in vase life relative to dry-shipped flowers (Halevy and Mayak, 1981). Accordingly, dry handling may also be worth examining for other floral species. For example, gerbera flowers, previously prescribed to be held in water before packing and shipping can also benefit from dry handling (Reid and Macnish, unpublished data). The benefits of dry handling are likely to be greatest when flowers are handled and transported at low temperatures. Cevallos and Reid (2001) reported that the vase life of dry-stored carnation, daffodil, iris, narcissus, rose and tulip flowers was greatest when storage temperatures were maintained below 10°C. In conclusion, our findings provide support for a re-evaluation of the practice of hydrating flower stems immediately after harvest. Our data showing that dry handling rose flowers is associated with reduced transportation-related damage and maintenance of optimal water relations during vase life highlight the potential of this alternative postharvest strategy for maximizing flower quality and longevity. Considering the higher volume and weight of flowers transported following hydration, which translates into higher costs of transportation and handling, the use of dry handling in combination with maintenance of the cool-chain represents an excellent opportunity to improve the postharvest performance of selected cut flowers. ACKNOWLEDGEMENTS We thank Rosen Tantau (Ecuador and Colombia) and the Elite Flower for providing flowers and logistical assistance with experiments. Literature Cited Cevallos, J.C. and Reid, M.S. 2001. Effect of dry and wet storage at different temperatures on the vase life of cut flowers. HortTechnology 11:199-202. de Witte, Y. and van Doorn, W.G. 1988. Identification of bacteria in the vase water of roses, and the effect of the isolated strains on water uptake. Scientia Hort. 35:285-291. Evans, R.Y. and Reid, M.S. 1988. Changes in carbohydrates and osmotic potential during rhythmic expansion of rose petals. J. Am. Soc. Hort. Sci. 113:884-888. Goszczynska, D. and Rudnicki, R.M. 1983. Long-term storage of bud-cut carnations. Acta Hort. 141:203-212. Halevy, A.H. and Mayak, S. 1981. Senescence and postharvest physiology of cut flowers. Part 2. Hort. Rev. 3:59-153. Kuiper, D., van Reenen, H.S. and Ribot, S.A. 1996. Characterisation of flower bud opening in roses; a comparison of Madelon and Sonia roses. Postharvest Biol. Technol. 9:75-86. Mayak, S. and Halevy, A.H. 1971. Water-stress as the cause for failure of flower bud opening in iris. J. Am. Soc. Hort. Sci. 96:482-483. Mokhtari, M. and Reid, M.S. 1995. Effects of postharvest desiccation on hydric status of cut roses. p.489-495. In: A. Ait-Oubahou and M. El-Otmani (eds.), Postharvest physiology, pathology and technologies for horticultural commodities: Recent Advances. Institut Agronomique et Veterinaire Hassan II, Agadir, Morocco. Nowak, J. and Rudnicki, R.M. 1990. Postharvest handling and storage of cut flowers, florist greens, and potted plants. Timber Press Inc., Portland, Oregon, U.S.A. Reid, M.S. 2002. Postharvest Handling Systems: Ornamental Crops. p.315-326. In: A.A. Kader (ed.), Postharvest technology of horticulture crops, 3rd ed. University of California, Oakland, California, U.S.A. van Doorn, W.G. 1997. Water relations of cut flowers. Hort. Rev. 18:1-85. van Doorn, W.G. and de Witte, Y. 1991. Effect of bacterial suspensions on vascular occlusion in stems of cut rose flowers. J. Appl. Bacteriol. 71:119-123. van Doorn, W.G. and D’hont, K. 1994. Interaction between the effects of bacteria and dry 218
storage on the opening and water relations of cut rose flowers. J. Appl. Bacteriol. 77:644-649. Zagory, D. and Reid, M.S. 1986. Role of vase solution microorganisms in the life of cut flowers. J. Am. Soc. Hort. Sci. 111:154-158.
Tables
Table 1. Changes in weight of ‘Charlotte’ rose flower bunches during processing for export at the farm in Colombia, shipment, and rehydration upon arrival in California. Flowers were harvested and immediately hydrated or not hydrated in a postharvest solution for 24 h at 2°C. Flowers were then shipped dry from Colombia to California where they were rehydrated for 24 h at 0°C. Weight proportion (%) data are expressed relative to the initial harvest weight. Farm treatment No hydration Plus hydration Z
During transport from greenhouse -1.3 aZ +5.0 b
During storage or hydration +3.2 a +5.1 b
During shipment -4.8 NSY -5.1
During rehydration in California +11.2 b +6.6 a
Total after rehydration +8.3 a +11.6 b
Means (n=3) followed by different letters are significantly different (P0.05).
Y
Table 2. Vase life (days) of ‘Black Magic’, ‘Charlotte’, ‘Freedom’, ‘Osiana’ and ‘Vendela’ rose flowers at 20°C. Flowers were harvested and immediately hydrated or not hydrated in a postharvest solution for 24 h at 2°C. Flowers were then shipped dry from Colombia or Ecuador to California where they were rehydrated for 24 h at 0°C and placed into a vase solution. Farm treatment No hydration Plus hydration Z
‘Black Magic’ 6.7 bZ 3.3 a
‘Charlotte’ 6.1 NSY 5.1
‘Freedom’ 14.4 NS 13.7
‘Osiana’ 20.2 b 17.4 a
‘Vendela’ 16.3 NS 16.1
Means (n=12) followed by different letters are significantly different (P0.05).
Y
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Bruised petals per flower
Figures
3
b
2 1
a
0 No hydration
Plus hydration
Fig. 1. Number of petals per ‘Vendela’ rose flower that showed bruising after an 8-day dry shipment from Ecuador to California. Flowers were harvested and immediately hydrated or not hydrated in a postharvest solution for 24 h at 2°C prior to shipment. Data (Means±S.E.M., n=24) followed by different letters are significantly different (P
