Short communication
Postharvest vase life of two flowering
Eucalyptus
species
K.L. Delaporte, A. Klieber, M. Sedgley *
Department of Horticulture,Viticulture and Oenology,The Uni6ersity of Adelaide,Waite Campus,P.M.B.1,Glen Osmond,
Adelaide,SA5064,Australia
Received 4 November 1999; accepted 14 February 2000
Abstract
Continuous application of 0.5 – 5.0% sucrose in the vase solution reduced vase life ofEucalyptus tetragonaflowers, from \13 days for the reverse osmosis (RO) water control toB10 days; vase life ofEucalyptus youngianawas not
affected by up to 2% sucrose. Pulsing with 0.5 – 10% sucrose, in conjunction with cold dry storage at 3°C for 1 – 2 weeks, had no effect on vase life ofE.tetragonaflowers, which had a subsequent vase life of 11 – 12 days regardless of cold storage period. Citric acid in vase and pulsing solutions did not affect vase life of either species. Overall flower life was the vase life-limiting factor. The usefulness ofE.youngianafor flowers is limited due to excessive nectar and pollen drop. Significant differences in vase life of about 50% were found between individual plants ofE.tetragonaand
E.youngiana. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:Postharvest;Eucalyptus; Vase life; Sucrose; Cold storage; Citric acid; Floriculture
www.elsevier.com/locate/postharvbio
1. Introduction
Some species from the genusEucalyptusL. He´r are recognised on world floriculture markets as foliage filler crops, but little attention has been paid to the flowers and buds, which have poten-tial as features in floral arrangements (Sedgley, 1998). There are many species that may prove suitable, and research is required into production, postharvest handling and varietal selection.
Studies to date have focussed on the production and postharvest care of eucalypt foliage, indicat-ing low levels of sucrose may be beneficial to vase life (Jones et al., 1994; Wirthensohn et al., 1996), although levels of 10% caused leaf browning and damage (Jones and Sedgley, 1993; Jones et al., 1994). Dry storage at cool temperatures (1 – 5°C) is possible for up to 30 days with no reduction in vase life; however, higher storage temperatures reduce vase life significantly (Forrest, 1991; Jones et al., 1993, 1994; Wirthensohn et al., 1996).
A selection and crossing program was com-menced at the University of Adelaide over 10 years ago to identify and develop Eucalyptus spe-* Corresponding author. Tel.:+61-8-83037242; fax:+
61-8-83037116.
E-mail address:[email protected] (M. Sed-gley)
cies for a range of uses including cut foliage, flower and bud production (Ellis et al., 1991; Wirthensohn et al., 1999). There is considerable variation across species and genotypes, and the potential for development of hybrids and superior genotypes with significantly increased vase life has been demonstrated (Wirthensohn et al., 1996).
In this preliminary study the optimal posthar-vest holding conditions were inposthar-vestigated for two
Eucalyptus species with different floral appear-ances. Eucalyptus tetragona has clustered small flowers with white stamens, with opposite grey leaves and square stems covered in a thick layer of wax (Wirthensohn and Sedgley, 1996). In con-trast, Eucalyptus youngiana has large individual flowers of up to 8 cm in diameter with stamens varying from yellow to deep red.
2. Materials and methods
2.1. Plant material
E. tetragona (R. Br) F. Muell. material was from six seedling trees between 2.5 and 4.5 years
of age in the Laidlaw Plantation, The University of Adelaide, South Australia (latitude 34°58%S. longitude 138°38%E). Plants were grown under conditions of summer irrigation and quarterly fertiliser application. Material from E. youngiana
F. Muell. (six trees) was from 20- to 25-year-old seedling trees in the Monarto Woodland, Calling-ton, South Australia (latitude 35°58%S. longitude 139°25%E). Trees were under natural Mediter-ranean climate conditions with no supplementary irrigation or fertiliser.
Stems, between 15 and 40 cm in length, were harvested from all species when the first one or two flowers had opened. They were cut from the tree, left dry for up to 2 h, and brought to the laboratory as quickly as possible. The lower leaves were removed, the stems recut (diagonal cut removing lower 10 – 20 mm of stem) and placed in RO water until allocation to treatments.
2.2. Vase life of flowers and lea6es
The number of flowers on each stem was recorded at harvest, after pulsing and then daily as one of four stages: 1, not open; 2, operculum
Table 1
Effect of continual sucrose on vase life of flowers and leaves, flowers opening after harvest and time to negative weight change for
E.tetragonaandE.youngianastems
Time to negative weight Flowers open after
Vase life (days)a
harvest (%) change (days)
Flowers Leaves
Control+citric acid (pH 3.5)
3.9a 10.2bc 13.1b 73.1a
0.5% sucrose+citric acid (pH 3.5)
4.0a 66.3a
11.1bc 1.0% sucrose+citric acid (pH 3.5) 9.5bc
54.0a 3.3a
8.1c
2.0% sucrose+citric acid (pH 3.5) 10.2c 8.8c 10.1c
5.0% sucrose+citric acid (pH 3.5) 62.3a 3.9a
E. youngiana
68.2a 2.7a
8.1a
Control (pH 6–7) 12.7a
8.3a 12.4a
0.5% sucrose+citric acid (pH 3.5)
11.1a 13.5a
1.0% sucrose+citric acid (pH 3.5) 53.9a 3.3a
2.0% sucrose+citric acid (pH 3.5) 10.7a 12.7a 56.4a 3.8a
Table 2
Effect of sucrose pulsing and cold storage on vase life of flowers and leaves, flower opening after harvest and time to negative weight change forE.tetragonastems
Flower open after
Vase life (days)a Time to negative weight change (days)
0.5% sucrose+citric acid (pH 3.5)
11.0a
2.0% sucrose+citric acid (pH 3.5) 17.2a 87.0a 10.1a 16.6a 83.8a
11.4a 10.2a
10.0% sucrose+citric acid (pH 3.5)
Cold storage
aData are averages of three stems each of six plants (as replications) with five sucrose×three cold treatments. Different superscripts indicate significant differences in a column atPB0.05.
lift; 3, flower fully open; 4, flower wilt or stamen drop. Vase life of flowers was considered termi-nated when more than 50% of the flowers were at stage 4, i.e. stamens were wilting and dropping from the hypanthium, or inferior ovary, of the flower. The percentage of flowers open for each stem was calculated as the maximum number of flowers at stage 2 and 3 throughout the assessment period, divided by the total number of flowers on that stem. The general appearance and colour of the leaves was recorded daily, and vase life of leaves was considered terminated when more than 50% of leaves showed 50% desiccation and brown-ing. Fresh weight and water uptake of each stem were measured daily, allowing the calculation of the first day of negative weight gain, indicating the onset of vascular blockage. Solutions were renewed daily as no biocide was used.
2.3. Experimental treatments
2.3.1. Continual sucrose
Stems of E. tetragona and E. youngiana were placed in solutions containing reverse osmosis (RO) water (pH 6 – 7) (control), RO water+0.05 g l−1 citric acid (CA) (AnalaR, BDH Chemicals, Australia) (pH 3.5), 0.5% sucrose (AR Bulk, AJAX
Chemicals, Australia)+RO water+CA (pH 3.5), 1.0% sucrose+RO water+CA (pH 3.5) or 2.0% sucrose+RO water+CA (pH 3.5), with an addi-tional solution of 5.0% sucrose+RO water+CA (pH 3.5) forE.tetragona. Vase life was assessed at 22°C in a controlled temperature environment, with 12-h day/night cycles under standard fluores-cent lights (5.5mmol m−2s−1), representing super-market display conditions.
2.3.2. Sucrose pulsing and cold dry storage
2.4. Statistical analysis
The statistical designs (Randomised Complete Block Design) were: (1a) continual sucrose (E.
tetragona) — five plants (as replicates) with six sucrose treatments and three stems per treatment (5×6×3=90 stems) with stems per plant ran-domly assigned to sucrose treatments; (1b) contin-ual sucrose (E. youngiana) — six plants (as replicates) with five sucrose treatments and three stems per treatment (6×5×3=90 stems) with stems per plant randomly assigned to sucrose treatments; and (2) sucrose pulsing and cold stor-age (E.tetragona) — three storage periods for six plants (as replicates) with five sucrose treatments and three stems per treatment (3×6×5×3=
270 stems) with stems per plant randomly allo-cated to pulses and storage periods. General analysis of variance was used to determine the
effect of the treatments on the criteria measured. One-way analysis of variance was used to deter-mine differences between plants within a species. The data were tested using GENSTAT 5 Release 4.2. (PC/Windows NT, 1997, Lawes Agricultural Trust, Rothamsted Experimental Station) with L.S.D. used where appropriate.
3. Results and discussion
The maximum vase life of E. tetragonaflowers and leaves, was observed at 13 and 17 days in RO water respectively, with no effect of citric acid (Table 1). Sucrose addition, even at low levels, reduced the vase life. Continual high sucrose (5.0%) induced leaf margin browning, and has-tened desiccation. Continual sucrose did not in-crease the percentage of flowers open after harvest
Table 3
Effect of plant on vase life of flowers and leaves, flower opening after harvest and time to negative weight change forE.tetragona
andE.youngianastems
Vase life (days)a Flower open after Time to negative weight harvest (%) change (days)
Flowers Leaves
E. tetragonacontinual sucrose
11.9bc 40.9c
E. tetragonasucrose pulsing and cold storage
Plant 2 14.0a 20.0a 79.7b 11.0a
E. youngianacontinual sucrose
Plant 1 8.5bc 15.5a 41.5bc 2.7b
and had no effect on time to weight change. The maximum vase life of E. youngiana flowers and leaves was greater than 11 and 13 days, respectively, but contrary to E. tetragona, con-tinuous sucrose exposure up to 2% did not af-fect vase life. The other parameters were also unaffected. The most limiting vase life criterion was flower life, with flowers showing symptoms of stamen desiccation and drop, as well as hy-panthium desiccation and abscission, at the end of their life.
There was no effect of citric acid or sucrose pulsing on any of the criteria measured on stems of E. tetragona that were subsequently held in water, with or without cold storage (Table 2). Vase life ranged from 10 to 11 days for flowers and from 15 to 17 days for leaves. Although statistically significant differences were recorded for each of the cold storage periods for the criteria of vase life of leaves, percent flowers opening after harvest and time to negative weight change, the limiting factor was the life of the flowers. Regardless of cold storage of up to 2 weeks at 3°C, vase life was 11 days; this would allow for distribution by air anywhere in the world.
Both E. tetragona and E. youngiana exhibited considerable differences between plants (Table 3). For example, E. tetragona plant 2 was iden-tical in both trials and showed the longest vase life in both. Plant 5 was identical in both trials, and in both trials showed medium vase life of flowers. Visual observations of these plants showed very similar morphology, with minor variation in flower size and number of flowers per stem. The six plants tested for E. youngiana
showed variation in vase life of flowers from 7 to 11 days. The most noticeable variation was shown in the percentage of flowers opening after harvest, where values ranged from 35 to 82%. With the exception of plant 1, those plants with the longest vase life had the lowest number of flowers opening after harvest, and the greatest time to negative weight change, indicating a possible positive correlation between flower opening and rate of senescence.
Visual observations of E. tetragona did not reveal any detrimental features of the species,
with little nectar production, insignificant pollen release and limited stamen drop. Undesirable features recorded for E. youngiana included the secretion of considerable quantities of nectar from each flower during the first 3 days after opening, and the dropping of large quantities of pollen during the same period.
For the two species tested, pre-harvest health of the plant, time of harvest and genotype may have an effect on subsequent vase life. Improve-ment of postharvest longevity is possible through testing a range of genotypes and selec-tion of those with a long vase life for further development and breeding. It is likely that vase life is influenced by a combination of a number of heritable components, as was found in ger-bera (Wernett et al., 1996). Eucalypt breeding and selection could be used to develop geno-types with superior floral attributes and posthar-vest life.
Acknowledgements
This research was supported by the Playford Memorial Trust and the Australian Landscape Trust. Thanks also to State Flora and Forestry SA, for access to the Monarto Woodland and Biometry SA for statistical advice.
References
Ellis, M., Sedgley, M., Gardner, J.A., 1991. Interspecific pol-len-pistil interaction in Eucalyptus L’He´r. (Myrtaceae): the effect of taxonomic distance. Ann. Bot. 68, 185 – 194. Forrest, M., 1991. Post harvest treatment of cut foliage. Acta
Hort. 298, 255 – 261.
Jones, M., Sedgley, M., 1993. Leaf waxes and postharvest quality ofEucalyptusfoliage. J. Hort. Sci. 68, 939 – 946. Jones, R.B., Truett, J.K., Hill, M., 1993. Postharvest
han-dling of cut immature Eucalyptus foliage. Aust. J. Exp. Agric. 33, 663 – 667.
Jones, R.B., Truett, J.K., Allen, T., 1994. Extending Euca
-lyptusvase life. Aust. Hort. 92, 43 – 47.
Wernett, H.C., Wilfred, G.J., Sheehan, T.J., Lyrene, P.M., Martin, F.G., White, T.L., Powell, G.P., Wilcox, C.J., 1996. Postharvest longevity of cut flower Gerbera II. Heritability of vase life. J. Am. Soc. Hort. Sci. 121, 222 – 224.
Wirthensohn, M.G., Sedgley, M., 1996. Epicuticular wax structure and regeneration on developing juvenile Euca
-lyptusleaves. Aust. J. Bot. 44, 691 – 704.
Wirthensohn, M.G., Sedgley, M., Ehmer, R., 1996. Produc-tion and postharvest treatment of cut stems of Eucalyp
-tusL. He´r. foliage. HortScience 31, 1007 – 1009.
Wirthensohn, M.G., Collins, G., Jones, G.P., Sedgley, M., 1999. Variability in waxiness ofEucalyptus gunniifoliage for floriculture. Sci. Hortic. 82, 279 – 288.
