Effects of cold storage methods on vase life and physiology of cut waratah inflorescences (Telopea speciosissima, Proteaceae)

Scientia Horticulturae, 29 (1986) 163--171

163

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

EFFECTS OF COLD STORAGE METHODS ON VASE LIFE AND PHYSIOLOGY OF CUT WARATAH INFLORESCENCES (TELOPEA SPECIOSISSIMA, PROTEACEAE)

JOHN D. FARAGHER

Horticultural Research Institute, Knoxfield, Department of Agriculture and Rural Affairs, P.O. Box 1 74, Ferntree Gully 3156, Vic. (Australia) (Accepted for publication 20 December 1985)

ABSTRACT Faragher, J.D., 1986. Effects of cold storage methods on vase life and physiology of cut waratah inflorescences (Telopea speciosissima, Proteaceae). Scientia Hortic., 29: 163--171. The effects of long-term, dry cold storage on the vase life and physiology of waratah inflorescences (Telopea speciosissima R.Br.) was investigated. Storage at 0 or 2°C and 100% RH for 2 weeks did not reduce the subsequent vase life at 20°C, but storage at 0°C for 4 weeks reduced it from 8 days in fresh inflorescences to less than 6 days. Storage at 4°C for 4 weeks further shortened vase life to 3 days, and storage at 80% RH reduced vase life compared with storage at 100% RH. Harvest maturity had no significant effect on post-storage vase life. Storage also reduced subsequent flower opening on the inflorescence. The shorter vase life of cold-stored waratahs was associated with earlier changes in properties of the inflorescence which normally accompanied senescence of fresh waratahs; decreases in water uptake and flower and bract fresh weights, and increases in nett water loss, perianth abscission and ethylene production by flowers. That is, cold storage advanced subsequent senescence of the inflorescence at 20°C, apparently because ageing had occurred during cold storage. Keywords: flower senescence; flower storage; protea.

INTRODUCTION W a r a t a h ( T e l o p e a speciosissima R . B r . , P r o t e a c e a e ) is a p r o m i s i n g n e w c u t - f l o w e r c r o p , p a r t i c u l a r l y in A u s t r a l i a w h e r e it is i n d i g e n o u s . F u t u r e m a r k e t i n g o f w a r a t a h s m a y r e q u i r e several w e e k s c o l d s t o r a g e t o l e n g t h e n t h e p e r i o d o f s u p p l y a n d t o a l l o w e c o n o m i c a l sea s h i p m e n t t o e x p o r t m a r k e t s . T h e r e s p o n s e o f w a r a t a h s , a n d o t h e r P r o t e a c e a e f l o w e r s , to longt e r m c o l d s t o r a g e has n o t b e e n t h o r o u g h l y i n v e s t i g a t e d . W a r a t a h s w e r e s t o r e d a t 0.5°C f o r 9 - - 1 0 d a y s a n d t h e s u b s e q u e n t vase life was s h o r t e n e d b y 30% ( W o r r a l l , 1 9 8 3 ) . R e s u l t s o f e x p e r i m e n t s w i t h Protea sp. are v a r i a b l e a n d i n c o n s i s t e n t . M e y n h a r d t ( 1 9 7 6 ) r e p o r t e d t h a t several s p e c i e s c o u l d

0304-4238/86]$03.50

© 1986 Elsevier Science Publishers B.V.

164 be successfully stored at 2°C for 6 weeks, but Jacobs (1981) reported that some of those listed by Meynhardt (1976) and other species had an unsatisfactory vase life after 3 weeks at 2°C. It has also been suggested that higher storage temperatures, of 2--8°C, may be more appropriate for P r o t e a (Halevy and Mayak, 1981). The aims of the present study were: (1) to investigate the effects of cold storage, and the components of the storage technique (temperature, humidity and duration), on the vase life and quality of the inflorescence; (2) to investigate the possible physiological mechanisms affecting vase life and flower quality after cold storage.

MATERIALS AND METHODS - - The waratah inflorescence is a terminal raceme of 150-200 red flowers surrounded by red bracts, and is illustrated by Faragher {1986). In this work, the term inflorescence includes flowers, bracts, stems a n d leaves, and the term flower refers to the individual flowers of the raceme. Inflorescences were cut from up to 40 seed-grown plants and transported to the laboratory, with stems in water, within 1 h. Inflorescences were cut when between 25 and 33% of the flowers were open, as this was the normal stage of development at commercial harvest. In an experiment to test the effect of maturity on response to cold storage, inflorescences were cut when 6, 27 or 48% of flowers had opened. Stems were cut to 30 cm in length, one-third of the leaves were removed and the inflorescences were dipped in Rovral fungicide (iprodione, May and Baker, Australia, 1 g 1-1).

Inflorescences.

treatments. - - Several independent experiments were carried out to investigate the effects of cold storage duration, humidity and temperature and the effect of flower maturity. In each experiment, fresh, unstored flowers were the controls and 6--8 replicate inflorescences were used. The storage conditions for each experiment are shown in the tables. Cold storage was without water. The temperatures used were 0.0 + 0.5, 2 + 1 or 4 -+ 1°C. Humidities were 85 -+ 5% inside a fibreboard carton, or close to 100% with free water present in a loosely closed polyethylene bag (low-density polyethylene ca. 38 pm thick). Storage durations were 0 (fresh), 2 or 4 weeks. After cold storage, stems were re-cut to 3 cm and placed in deionised water. For observation of vase life, flower opening and changes in physiological properties, inflorescences were held in water at 20 -+ 1°C and 60% RH, with continuous white fluorescent light of 5 W m -2 irradiance. In one experiment the effect of chlorine bactericide on vase life after cold storage was investigated, and sodium dichloroisocyanurate was added to the vase water at 25 mg 1-1 available chlorine. The vase water, or chlorine solution, was changed every second day. Experimental

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M e a s u r e m e n t s . - - The end of vase life was defined as when there was readily

discernible wilting and color change from bright-red to blue-red in at least one-third of the flowers and all of the bracts. Generally, wilting and blueing occurred at the same time, and these changes occurred in the bracts when they were also visible in one-third of the flowers. Flower opening was expressed as the percentage of flowers on the inflorescence which had opened. Fresh weight and ethylene production were measured on representative bracts and the outermost (oldest) flowers, which were sampled from the inflorescence at intervals during vase life. Water uptake, transpiration and nett water loss (transpiration minus uptake) by the inflorescence were measured. Measurements were made as described previously (Faragher, 1986). Perianth abscission was evaluated in two ways, firstly by noting the time when it was first visible in the oldest flowers, and secondly by calculating an abscission rating, i.e. the percentage of flowers in which abscission had occurred in a sample of two flowers from each of eight inflorescences RESULTS

o f c o l d storage o n vase life, f l o w e r o p e n i n g a n d quality. -- Vase life was not shortened by 2 weeks storage, but was shortened when storage duration was increased to 4 weeks (Table I). Vase life was shortened when

Effects

TABLE I E f f e c t o f cold storage d u r a t i o n o n vase life of w a r a t a h s . Storage was at 2°C a n d 100% RH. M e a n s f o l l o w e d b y a d i f f e r e n t l e t t e r differ significantly (P < 0.05, D u n c a n ' s m u l t i p l e range test) Storage d u r a t i o n (weeks)

Vase life (days)

0 2 4

8.3 a 8.2 a 4.3 b

TABLE II

E f f e c t of h u m i d i t y in cold storage o n vase life o f w a r a t a h s . Storage was at 2°C for 2 weeks. M e a n s f o l l o w e d b y a d i f f e r e n t l e t t e r differ significantly (P ~< 0.05, D u n c a n ' s m u l t i p l e range test) Storage t r e a t m e n t

Vase life (days)

No storage 100% R H 80% R H

8.3 a 8.2 a 6.5 b

166 storage h u m i d i t y was r e d u c e d f r o m 100 to 80% R H (Table II) and w h e n storage t e m p e r a t u r e was increased f r o m 0 to 4°C (Table III). I n f l o r e s c e n c e m a t u r i t y (6, 27 o r 48% flowers o p e n w h e n c u t ) had n o significant e f f e c t on vase life after cold storage f o r 4 weeks at 2°C and 100% R H (P ~< 0.05, D u n c a n ' s multiple range test, d a t a n o t s h o w n ) . Cold storage r e d u c e d subs e q u e n t flower opening, c o m p a r e d with u n s t o r e d inflorescences, in waratahs c u t at three maturities (Table IV}. O t h e r m i n o r effects o f cold storage o n quality were the occasional fungal i n f e c t i o n despite fungicide t r e a t m e n t , and wilting o f the inflorescence during storage at 80% RH, a l t h o u g h the inflorescences regained t u r g o r after transfer t o water. TABLE III Effect of cold-storage temperature on vase life of waratahs. Storage was for 4 weeks at 100% RH. Means followed by a different letter differ significantly (P < 0.05, Duncan's multiple range test) Storage treatment

Vase life (days)

No storage 0°C 4°C

7.9 a 5.8 b 3.1 c

TABLE IV Effect of cold storage on flower opening during vase life of waratahs. Inflorescences were cut at three stages of maturity, with 6, 27 or 48% of flowers open. Storage was for 4 weeks at 2°C and 100% RH. For each maturity, mean values followed by a different letter differ significantly (P < 0.05, Duncan's multiple range test) Inflorescence maturity (% flowers open)

Storage treatment

Flower opening (%)

6

No storage Storage

45 a 16 b

27

No storage Storage

60 a 40 b

48

No storage Storage

72 a 53 b

Effects o f cold storage on physiology o f the inflorescence. -- The effects o f storage d u r a t i o n on the s u b s e q u e n t p h y s i o l o g y o f the inflorescence d u r i n g vase life at 20°C are s h o w n in Fig. 1. A f t e r 2 weeks storage, the fresh weights o f flowers and bracts during vase life were n o t significantly less t h a n t h o s e o f fresh, u n s t o r e d waratahs ( c o m p a r i s o n o f m e a n s b y t-test, at P ~< 0.05, at t h e same sampling times} (Fig. 1A,B}. H o w e v e r , after 4

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weeks storage, fresh weights were significantly less than those in fresh~ unstored waratahs (Fig. 1A,B). Perianth abscission was visible immediately after removal from both 2 and 4 weeks storage, b u t did not occur in fresh flowers until after 4 days at 20°C (Fig. 1A). Water uptake by the influorescence was less after 2 weeks storage than in fresh inflorescences, but after 4 weeks storage uptake was similar to that in the fresh inflorescences (Fig. 1C). The cumulative nett water loss from the inflorescences increased with time at 20°C (Fig. 1D). Inflorescences stored for 2 weeks had the same water loss as fresh inflorescences, b u t those stored for 4 weeks had a much greater nett water loss (Fig. 1D). The increase in ethylene production by flowers during senescence was advanced and stimulated by prior storage (Fig. 1E). After 4 weeks storage, the maximum rate occurred immediately after transfer from 2 to 20°C, and was approximately five times the maxim u m rate in fresh flowers. The effects of storage temperature on the physiology of inflorescences at 20°C are shown in Fig. 2. As storage temperature was increased from 0 to 4°C, the fresh weight of flowers and bracts decreased more rapidly during vase life (Fig. 2A,B). This was associated with earlier perianth abscission as storage temperature increased (Fig. 2A). The percentage of abscised perianths in a sample of the oldest flowers from inflorescences (abscission rating) increased most rapidly in stored flowers, particularly in those stored at 4°C (Fig. 2C). Water uptake was less after storage at both 0 and 4°C than in fresh inflorescences (Fig. 2D). Nett water loss was not significantly greater in inflorescences stored at 0°C than in fresh ones, but it was greater after storage at 4°C (Fig. 2E). Chlorine bactericide added to the vase water increased the vase life of fresh waratahs b u t did n o t significantly increase vase life after cold storage for 4 weeks at 2°C and 100% RH (P < 0.05, t-test, data not shown). DISCUSSION

Cold storage was successfully used to hold waratahs without loss of vase life for 2 weeks, and with a small, acceptable loss of life for 4 weeks. The loss of vase life after extended cold storage was the only major, adverse effect of storage. Cold storage also reduced flower opening, but this is probably not a commercial disadvantage. Vase life was very sensitive to

Fig. 2. Effects of storage t e m p e r a t u r e on changes in the waratah inflorescence during vase life at 20°C. o, fresh n o t stored (Fr); o, storage at 0°C and 100% R H for 4 weeks; s,, storage at 4°C. Values are means of 8 replicates -+ standard errors. A. F l o w e r fresh weight, o u t e r m o s t flowers. The t i m e w h e n perianth abscission was first visible is indicated by arrows and the letter a. B. Bract fresh weight. C. Perianth abscission rating, o u t e r m o s t flowers (see Materials and Methods for calculation). D. Water u p t a k e by the inflorescence. E. N e t t water loss (cumulative) f r o m the inflorescence.

170 storage duration, temperature and humidity. Storage for 4 weeks under the optimum conditions of 0°C and 100% RH shortened vase life from 8 days in fresh waratahs to 6 days. This 2-day, 25%, loss of life is probably the maximum which could be tolerated commercially, and so 4 weeks is probably the maximum feasible storage life. It may be valuable to know the more detailed effects of storage duration, for example the effects of 3, 4 and 5 weeks storage. When storage temperature was higher than 0°C, or humidity reduced from 100 to 80% RH, vase life was markedly shortened, so in practice the careful use of optimum storage conditions will be critical for subsequent life of waratahs. It has been assumed that the major effect of storage in polyethylene bags was to increase the humidity to close to 100% RH, but changes in 02 or CO2 concentrations in the bags cannot be ruled out. The loss of vase life in m y experiments was less than that reported by Worrall (1983), who found a 30% loss of life after 10 days storage at 0.5°C. The slower loss of life in m y experiments could be due to higher storage humidity, use of more mature inflorescences, or other differences between the inflorescences. The actual vase life of 6--8 days appears short for flowers of the Proteaceae, which are assumed to have long lives. This is probably because waratahs do senesce more rapidly than other Proteaceae flowers, and because relatively severe conditions were used to measure vase life with continuous 20°C, air circulation and light. Senescence of cold-stored waratahs during vase life at 20°C followed the same pattern as senescence in fresh, unstored inflorescences, but the events were advanced. The sequence of senescence events appears to involve decreased water uptake, nett water loss, perianth abscission and increased ethylene production as initial events, followed inevitably by loss of fresh weight in flowers and bracts, blueing and the end of vase life. The regulation of the initial events of waratah senescence is unclear. Nett water loss is an expected result of decreased water uptake. However, in at least one case, water loss increased but uptake did not decrease (4 weeks storage, Fig. 1C,D), so it appears that transpiration was increased, possibly as a result of increased cell membrane permeability during senescence (Mayak and Halevy, 1980; Faragher and Mayak, 1984). Abscission could be caused by nett water loss, or by the increased ethylene production in flowers (Halevy and Mayak, 1981; Reid, 1985). Ethylene promotes senescence of other flowers (Mayak and Halevy, 1980; Halevy and Mayak, 1981), but its role in waratahs remains to be determined. There was some evidence that ageing and senescence had proceeded during cold storage since abscission had started, flower ethylene production rates had increased and water uptake had decreased at the time of transfer from cold storage to 20°C. This suggests that the major effect of cold storage on the physiology of the waratah inflorescence was to allow ageing to occur in storage, so that when it was transferred to 20°C, ageing was already advanced and thus vase life was shortened. There was

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one other effect of cold storage on waratahs, which was to increase the rate of ethylene production by flowers after transfer to 20°C. This also occurs in roses (Faragher and Mayak, 1984) and several fruits, and it appears to be a typical response of some plant tissues to low temperatures (Wang, 1982). However, the significance of this ethylene in waratah flower senescence is not known. Chlorine bactericide treatment of vase water increased the life of fresh inflorescences, probably because it increased water uptake (Faragher, 1986). However, it did n o t increase vase life or water uptake of cold-stored waratahs. Thus, it appears that the effect of cold storage, which reduces water uptake, is somewhat different to the effect of ageing on uptake in freshly cut waratahs. It is concluded that dry cold storage of waratah inflorescences is feasible for a period of up to 4 weeks at 0°C and 100% RH, with only a 25% loss of vase life. At higher storage temperatures or lower humidities, loss of vase life would be greater unless storage time was shortened. The effects of cold storage are primarily due to advanced senescence, probably as a result of continued ageing during storage. ACKNOWLEDGEMENTS

I gratefully acknowledge the valued technical assistance of Fran Richardson, critical advice on the manuscript from Dennis Richards, and the supply of flowers by Mrs. J. Frank of Clematis and Mr. D. Nichols of Austflower, Gembrook.

REFERENCES Faragher, J.D., 1986. Post-harvest physiology of waratah inflorescences (Telopea speciosissima, Proteaceae). Scientia Hortic., 28 : in press. Faragher, J.D. and Mayak, S., 1984. Physiological responses of cut rose flowers to exposure to low temperature: changes in membrane permeability and ethylene production. J. Exp. Bot., 35: 965--974. Halevy, A.H. and Mayak, S., 1981. Senescence and post-harvest physiology of cut flowers. Part 2. Hortic. Rev., 3: 59--143. Jacobs, G., 1981. Post-harvest handling of proteas. In: P. Mathews (Editor), Growing and Marketing of Proteas, Vol. 1. Proteaflora Enterprises, Melbourne, pp. 40--51. Mayak, S. and Halevy, A.H., 1980. Flower senescence. In: K.V. Thimann (Editor), Senescence in Plants. CRC Press, Boca Raton, FL, pp. 131--156. Meynhardt, J.T., 1976. Proteas -- picking and handling. In: Farming in South Africa, Flower Ornamental Shrubs and Trees Series. No. B5/1976. Dep. Agric. Tech. Serv., Pretoria, S. Africa, 3 pp. Reid, M.S., 1985. Ethylene and abscission. HortScience, 20: 45--50. Wang, C.Y., 1982. Physiological and biochemical responses of plants to chilling stress. HortScience, 17 : 173--186. Worrall, R.J., 1983. Growing waratahs commercially. Aust. Hortic., 81 : 101--103.