Postharvest cut Eucalyptus foliage

Agr. Med. Vol. 137, 124-131 (2007) POSTHARVEST PHYSIOLOGY AND TECHNOLOGY OF CUT EUCALYPTUS BRANCHES: A REVIEW S. Pacifici1, A. Ferrante2, A. Mensuali-Sodi1*, G. Serra1 1 2 Scuola Superiore S. Anna, Piazza Martiri della Libertà 40, 56125 Pisa, Italy Dept. Produzione Vegetale, Università degli Studi di Milano, Italy SUMMARY - Cut Eucalyptus branches are important ornamental filler used in bouquet and floral decorations. Italy is at the first place as country production for cut foliage export in Europe and one of the first in the world wide. Floriculture industry must be very competitive and quality must be guaranteed from the growth to the end-user. In floriculture, marketing and product distribution are critical issues for all countries. The production area and selling markets may be very far from each others with long transportation periods. The storage and packaging systems play an important role for preserving quality and reducing transportation costs. In this review the postharvest physiology of cut eucalyptus branches are reported. Especially ethylene and respiration pattern such as the pulse treatments that can be useful for preserving quality. Key words: cut foliage, eucalyptus, ethylene, storage, packaging, vase life INTRODUCTION Cut greens are an important component of the floricultural industry, largely used for decoration as filler in floral compositions. They provide freshness and colour variety to arrangements and bouquets. Cut eucalyptus species are especially important for preparing arrangements of flowers that are naturally without leaves, such as gerberas and orchids. In many countries of the north Europe, in particular the UK, cut greens can be used for indoor decorations during winter time, providing a striking contrast to the wintry outdoor landscape. The increase of economic importance of cut foliage production in the Italian ornamental industry is a result of the reorganization of the internal production in response to a crisis period in the cut flower production. Word wide flower market has been becoming stronger and stronger for the flowers coming from the developing countries such as Colombia, Kenya etc., which can produce flowers at lower costs. Moreover, the globalization of the flower market led Italian growers to seek for alternative crops such as cut foliage. In addition, consumers are paying more attention to the appearance of floral compositions and foliage is now almost as important design element as the flowers themselves. The Italian area for cut foliage production was 1542 ha in 2005, with a total production of 1.3 million units with 85% of this cultivation realized in plain area, and regions principally involved were Liguria (58%), Campania (8.56%) and Tuscany (6.34%) (ISTAT, 2009). Data ISMEA-ISTAT reported that Italy in the 2006 imported 15% and exported 85% (on the economic value basis) cut foliage (Barsotto et al., 2008). Cut greens include many ornamental species and the most important are: Asparagus spp., Eucalyptus spp., Ruscus spp., Hedera spp., Polypodium spp. (ISTAT, 2006). *Corresponding author. Tel. +39050/2216512; Fax: +39050/2216524; E-mail: [email protected] 124 S. PACIFICI, A. FERRANTE, A. MENSUALI-SODI, G. SERRA BOTANY Eucalyptus belongs to Myrtaceae family and is native of the Australia and Tasmania. The most important species used for cut foliage production are: E. polverulenta (cv. Baby blue), E. cinerea, E. gunnii, E. nicholii, E. parvifolia, E. perriniana, E. pupulifolia and E. stuartiana. These ornamental trees are also popular for gum and essential oils production that can be extracted from leaves. Eucalyptus grows in mild, warm and tropical climates, but cannot live at temperatures lower than -5°C. In the recent years the cultivation area of eucalyptus for cut branches production is growing up. The plant is characterized by heterophylly that means the changing of leaf shape during development. Young leaves are sessile and rounded shaped, while the old leaves are provided of peduncles and have low ornamental value. Eucalyptus is a monoic plant with wind pollination and undergoes easily hybridization. Different species of eucalyptus are characterized by good adaptability to different soils and climatic conditions, high productivity, good longevity and stem resprouting. PRODUCTION AND HARVEST Eucalyptus species are cultivated in Mediterranean area and grow until 350 meters over the sea level. Usually the young plants are planted in spring or at the end of summer. Eucalyptus should be grown in climate with high humidity otherwise suffers of leaf border burning. It can grow in wide range of soils and with limited water supply. The soil optimum pH ranges from 5.5 to 6.5. The yield of cut foliage varied from 2.87 to 4.79 kg plant-1 (Forrest, 2002). Advisable planting density for other eucalyptus species are: 1-1.5 plant m-2 in E. cinerea and E. stuartiana, 1 plant m-2 in E. populifolia. Eucalyptus foliage can be harvested all year around with lower production in summer (August). The harvest begins on the lower branches that should be harvested to 40- 60 cm long. Cut branches can be harvested in immature (apical leaves are not completely expanded) or mature stage (leaf fully expanded without soft tips). For commercialization the leaves of cut foliage must be free of spots and injuries (mechanical or pathogen damages). Branches are grouped in 10 bunches for transport and marketing. The weight of each bunch usually ranges from 250 to 500 g. Harvesting time has an important influence on postharvest water losses. Usually, harvesting should be done in the morning when the temperature is cooler and the transpiration and metabolism of the foliage are slowed down. Seasonal changing and the harvest period in the year affect the vase life of eucalyptus branches: cut foliages harvested in summer show shorter vase life than those collected in winter (Ferrante et al., 2000). The maturity stage of branches, at the harvesting time, strongly affects the vase life. Environmental conditions during the different developmental stages also influence the leaf metabolism, in particular transpiration, respiration end ethylene production (Ferrante et al., 1998). The immature compared with mature branches are more sensitive to water stress and during vase life show apical bending, while the mature branches mainly show leaf desiccation (Ferrante et al., 1998). In Table 1 is reported vase life of different eucalyptus species. POST-HARVEST PHYSIOLOGY AND TECHNOLOGY The vase life of the most part of cut eucalyptus species is often satisfactory and does not need to be extended (Wirthensohn et al., 1996). However, there are some species that may get beneficial effects from treatments with preserving solutions, especially during summer periods such as E. parvifolia and E. gunnii (Ferrante et al., 1998). The vase life of E. parvifolia during May-June is below 10 days (Ferrante et al., 2000). 125 AGRICOLTURA MEDITERRANEA Table 1. – Vase Cut eucalyptus branches, environment. such as other cut foliage, durSpecies ing postharvest life undergo E. aggregata many physiological changes E. albida that may induce several disE. cinerea orders leading them to die. The senescence studies carE. ciccifera ried out on cut flowers and E. cordata foliage have greatly helped E. crenulata to find technological strateE. dalrympleana gies to prolong vase life of E. globulus cut eucalyptus foliage. The E. gunnii quality and the vase life of E. leucoxylon cut eucalyptus foliage essenE. linearis tially depend from the leaf E. maidenii health status. Senescence E. nicholii symptoms of cut eucalyptus foliage can be leaf wiltE. ovata ing, desiccation, rolling and E. paniculata necrosis. E. parvifolia However, the postharvest E. perriniana life of cut eucalyptus foliage E. polyanthemos depends from many internal E. populnea and external factors, which E. polverulenta may act synergistically reducing the vase life. ThereE. robusta fore it is difficult to identify E. sideroxylon the major physiological disE. stuartiana order that limits the postE. urnigera harvest life. The intensity of leaf colour is closely correlated with the quality of ornamental cut foliage. The concentration of chlorophyll is directly correlated with consumer’s attractiveness. In the floriculture industry the use of chlorophyll meter may be useful for estimating the quality of cut greens. Comparison studies on chlorophyll measurements in E. parvifolia were performed using no invasive method (SPAD) or analytical determinations (Pacifici et al., 2008b). Results were not satisfactory and for this species SPAD values are not an indicator of leaf senescence. Cut foliage show chlorophyll degradation when they are already senescent, therefore the chlorophyll content cannot be used as marker for evaluating the quality of cut E. parvifolia branches (Ferrante et al., 2002b; Ferrante et al., 2003a,b; Pacifici et al., 2008a,b). life (days) of Eucalyptus spp in different temperature Vase life Literature 35-40 Bazzocchi et al., 1987 13-14 Wirthensohn et al., 1996 14-30 Wirthensohn et al., 1996; Ferrante et al., 1998 35-40 Bazzocchi et al., 1987 30-35 Bazzocchi et al., 1987 9-10 Jones et al., 1993 31-35 Bazzocchi et al., 1987 30-35 Bazzocchi et al., 1987 15-34 Ferrante et al., 2005 30-35 Bazzocchi et al., 1987 30-35 Bazzocchi et al., 1987 40-45 Bazzocchi et al., 1987 35-40 Bazzocchi et al., 1987 35-40 Bazzocchi et al., 1987 35-40 Bazzocchi et al., 1987 13-31 Ferrante et al., 2000; 2002b; 2005; Pacifici et al., 2008b 35-40 Bazzocchi et al., 1987 40-50 Bazzocchi et al., 1987 35-40 Bazzocchi et al., 1987 30-35 Bazzocchi et al., 1987 30-35 Bazzocchi et al., 1987 30-35 Bazzocchi et al., 1987 30-35 Bazzocchi et al., 1987 40-45 Bazzocchi et al., 1987 The main postharvest problem of cut eucalyptus is the weight loss (during storage and transportation) and reduced water uptake (during vase life). Since the cut eucalyptus such as all cut greens are sold by weight and any reduction is directly translated in economic losses. Among eucalyptus species there are E. youngiana and E. tetragona that are grown for cut flowering branches production and the flower life is the vase life-limiting factor (Delaporte et al., 2000; Delaporte et al., 2005). Respiration, ethylene production and sensitivity Cut branches after harvest continue to live and all metabolic processes rapidly decline if not correctly handled. Respiration of eu- 126 S. PACIFICI, A. FERRANTE, A. MENSUALI-SODI, G. SERRA calyptus cut branches kept at 20°C increase up to three days of vase life with a rate that ranges from 2.5 to 10 mol CO2 h-1 g-1 FW than slightly decreased (Ferrante et al., 2003b). The ethylene is another important parameter that may affect the vase life of many cut flowers and foliage. The ethylene production of cut eucalyptus varies with the stage of leaf maturity. Cut immature branches have higher ethylene production compared to mature branches. In cut Eucalyptus parvifolia, the immature branches produce 6 nl h-1 g-1 FW (after 24 h in vase), while the mature branches produce half amount of ethylene about 3 nl h-1 g-1 FW. Analogous results were found in immature and mature branches of E. gunnii (Ferrante et al., 1998). However, ethylene production varies also from species to species. In cut E. gunnii branches the amount of ethylene ranges from 4 to 11 nl h-1 g-1 FW during the first 24 hours after harvest (Jones et al., 1993; Ferrante et al., 1998), while the ethylene production in E. cinerea ranges from 2-3 nl h-1 g-1 FW. Cut eucalyptus species can be considered ethylene insensitive, because exogenous applications of ethylene induced visible damage at 20 µL L-1, reducing the vase life by 19% compared to control. Since the ethylene concentration during the distribution chain or at retailer markets does not overcome 3 µL L-1 the cut eucalyptus foliage can be reasonably considered ethylene insensitive. Different behaviour was observed when cut eucalyptus was treated with 1 mM 1-aminocyclopropane-1-carboxylic acid (ACC) the ethylene precursor. Treatment ACC strongly reduced the vase life and induced complete leaf abscission (Ferrante et al., 2002a). Ethylene production and respiration trends were opposite during vase life and eucalyptus cannot be ascribed to climateric or no climateric pattern (Ferrante et al., 2003b). Storage and packaging conditions Environmental conditions during storage and transportation are extremely important for preserving quality of ornamental per- ishables. Floriculture items have to be often transported for long distances before they reach the selling markets and are highly susceptible to quality losses. The packaging systems play an important role in preventing water losses, product damage and reducing transportation costs. The optimal environmental conditions for cut foliage are low temperatures and high relative humidity in order to minimize water losses. Temperature should be as low as possible considering the freezing point of species. However, the common storage and transportation temperature ranges from 0 to 5°C. Low temperatures reduce all physiological processes, especially respiration and ethylene production. Temperatures close to 0°C should be preferred for long shipping distance, while higher temperatures around 5°C may be used for local commercialization (Reid and Ferrante, 2002). Dry storage is not advisable in these species, because the high transpiration surface of cut foliage induces a rapid water loss and subsequent wilting (Ferrante et al., 2002b). Recent studies on E. parvifolia showed that cut branches can be dry stored if sealed in plastic bags and kept at 4°C (Pacifici et al., 2008a, 2008b). Optimal results were obtained when a mild vacuum was applied to sealed bags reducing volume. In these experiments the air inside the bags was reduced but not completely removed. Cut eucalyptus branches dry stored in plastic bags under mild vacuum satisfactory can be stored until 6 days without any negative effect on subsequent vase life (Pacifici et al., 2008b). This period of time may be enough for the most common transport destinations. The maximum vacuum storage duration depends from the development stages at harvest of E. parvifolia. In fact, immature cut branches can be stored only for 3 days (Pacifici et al., 2008a). Vacuum storage is a common practise for preserving vegetables and fruits. In vacuum storage bags or in storage chambers equipped with controlled atmosphere the gas concentration continuously changes, due to plant tissue respiration generating a pas- 127 AGRICOLTURA MEDITERRANEA sive modified atmosphere (Knee and Aggarwal, 2000). The most important advantage of vacuum packaging applied to the cut foliage industry is the increase of loading capacity per unit of volume, reducing the transportation costs without compromising the produce quality. Wet storage of cut foliage, instead, is the most used method at the selling point or in farm before transportation. Cut E. gunnii was satisfactory stored for 4 weeks (Forrest, 1991) and cut E. parvifolia for 4 weeks (Ferrante et al., 2002b), without affecting the postharvest life (Tab. 2). The effect of different storage conditions on the vase life of E. parvifolia is reported in Tab. 2. Water stress and postharvest treatments The water stress may be a major problem for several cut foliage. The water stress is often caused by xylem occlusion, which may be induced by bacterial growth in the vase water (van Doorn, 1997). Weight losses of cut foliage may be avoided using chemicals that improve the hydraulic conductance or reducing the leaf transpiration in vase by treatments with surfactants and weak acids. During transportation the pulse treatments should be addressed to reduce water losses limiting transpiration. Many treatments have been used for improving the vase life of cut eucalyptus species (Tab. 3). The compounds tested are the same of those used for preserving cut flowers, which were studied alone or in combinations (i.e. Forrest, 1991; Wirthensohn et al., 1996; Ferrante et al., 2002a). The commercial preservative solutions recommended for cut foliage are a mix of several chemical compounds and most of them are not declaimed for patent reasons. Sugar: it is usually used in commercial formulations and is a source of food/energy for Table 2. – Effect of different postharvest environment conditions on the vase life (days) of E. parvifolia. Storage T°C Time storage Vase life Literature Cold wet 5°C 4 weeks 12.5±1.60 Ferrante et al., 2002b Forrest 1991. Cold dry 5°C 2 weeks 2.0 Ferrante et al., 2002b Cold wet 4°C 6 days 12.0±0.60 Pacifici et al., 2008a Mild cold vacuum (dry storage) 4°C 6 days 11.2±0.60 Pacifici et al., 2008a Room temperature 14°C day – 10°C night - 21.5±2.20 Ferrante et al.,2005 Room temperature 20°C - 14.0±0.66 Pacifici et al., 2008a Ferrante et al., 2002b Table 3. – Postharvest treatments to extend cut Eucalyptus spp. vase life (% of the control). Treatments Concentrations Species Vase life Literature AOA 1 mM E. parvifolia 5 Ferrante et al., 2002a Cobalt chloride 2 mM E. parvifolia 30 Ferrante et al., 2002a Glycerol 1 mM 20% E. parvifolia E. cinerea 53 n.d. Ferrante et al., 2001 Campell et al., 2000 Citric acid 150 mg L-1 E. parvifolia 56 Ferrante et al., 2001 Vaporgard 1% E. parvifolia 33 Ferrante et al., 2001 26 95 Wirthensohn et al., 1996 E. gunnii 20 Forrest, 1991 Sucrose + 8-HQS Sucrose + 8 HQC 10-20 g L-1 suc.+200 mg L-1 E.cinerea 8-HQS E. globulus 20 g L-1 suc. + 200 mg L-1 8-HQC STS 2 mM E. gunnii 16 Forrest, 1991 Triton X 0.01% E. parvifolia 0 unpublished 128 S. PACIFICI, A. FERRANTE, A. MENSUALI-SODI, G. SERRA cut ornamentals, especially for cut flowers. The most used sugar for making preservative solutions is the sucrose with concentrations ranging between 0.5 to 20%. The sugar must be supplied with biocides in order to inhibit bacteria growth. The sugar loading can be applied as pulse treatment (24-48 h) or as continuous treatments. Of course, the choice of one or another depends at which stage of the distribution chain the postharvest treatment is required. Cut eucalyptus species treated with sucrose have given opposite results depending from the species. Combinations of sucrose and 8-hydroxyquinoline sulphate (8-HQS) improved the vase life in E. globules and E. cinerea (Wirthensohn and Sedgley, 1996). Positive effect was obtained also in E. gunnii treated with sucrose and 8hydroxyquinoline citrate (8-HQC) (Forrest, 1991). Applications of sucrose in combinations with amino-oxyacetic acid (AOA) or 8-HQS were not able to extend the vase life of cut E. parvifolia, even if avoided the weight losses and improved the water uptake (Ferrante et al., 2003a). It has been found that high levels of sugars in leaf are the triggers of senescence (Sheen, 1990). In fact, it is well known that supplying sucrose to the plants leaves lose their primary function, since plants do not need to produce carbohydrates through photosynthesis and activate the leaf senescence for reducing transpiration (Reid and Ferrante, 2002). Ethylene inhibitors: treatments applied to cut eucalyptus species did not always satisfactory extend the vase life. The AOA slightly improve the vase life, while the cobalt chloride has been more efficient to extend the longevity of E. parvifolia cut foliage. Treatments with ethylene inhibitors were able to inhibit the ethylene production (Ferrante et al., 2002a). Treatments with silver thiosulphate (STS) did not increase the vase life of cut E. gunnii branches (Forrest, 1991). Biocides: they should be applied for reducing the number of bacteria in the vase water. Bacteria are the most important factors that limit the vase life of cut flowers (Aarts, 1957). Positive correlation has been found between bacteria obstruction and vessels occlusion in cut ferns of Adiantum raddianum (van Doorn et al., 1991). The ammonium quaternary salts (benzalkonium chloride) did not give any beneficial effect on vase life of E. cinerea, E. gunnii and E. parvifolia (Ferrante et al., 1998). These chemical compouds applied as pulse treatment for 48 h decreased the vase life and the leaf quality. The sodium hypochlorite (NaClO) is a commonly used biocide in water solution for cut flowers, unfortunately it was phytotoxic for E. parvifolia (data unpublished). On the contrary, pulse treatments with citric acid were able to improve the vase life of this species (Ferrante et al., 2001). The citric acid improves the vase life because reduces the pH and inhibits the bacterial growth. In fact, pH values of holding solution should range from 3 to 4. These values block the bacteria growth that may occlude vessels and inhibits water uptake. Surfactants: cut branches of E. parvifolia were treated with 0.01% Triton X®, a non ionic surfactant, with the aim to facilitate the water uptake through the stems. The results did not show significant difference between the vase life of treated and untreated branches (unpublished data). Antitraspirants and osmoregulators: treatment with an anti-transpirant Vaporgard® has not significantly increased the vase life, reducing the water uptake by limiting the leaf transpiration (Ferrante et al., 2001) of cut E. parvifolia branches. Anti-transpirants create a thin plastic film over the leaves avoiding the water losses through the stomata. Unfortunately, this treatment makes the cut branches sticky and unmarketable. Cut foliage of E. parvifolia treated with glycerol showed longer life compared with control (Ferrante et al., 2001). Analogous results were found in E. cinerea (Campbell et al., 2000). The glycerol induced a strong water stress at beginning of experiment inducing an increment of ethylene production (Ferrante et al., 2001). Glycerol absorbed by cells increases the water potential into leaves creating a new water flux along the stem. 129 AGRICOLTURA MEDITERRANEA CONCLUSIONS The quality of cut foliage can be guaranteed by harvesting the eucalyptus branches at the mature stage and during the coolest period of the day such as early in the morning, especially in spring-summer time. Postharvest treatments are only required for cut foliage that will be stored for long time or shipped for long distance and can be applied before or after storage/transportation. These treatments should be performed with chemical compounds that improve water uptake or reduce transpiration for avoiding the cut branches weight losses. Transportation should be performed dry in plastic bags associated with a mild vacuum. Storage can be performed in water or in sealed plastic bags. The vase water at retailers should be acidized to 3-4 pH using weak acids such as citric acid. Acknowledgements The work was supported by funds of MIPAAF, FLORPRO project 2006-2008 “Individuazione di tecniche di produzione, di conservazione e commercializzazione, finalizzate alla riduzione dell’impatto ambientale e all’ottimizzazione della qualità merceologica del prodotto”. Publication n° 9 REFERENCES AARTS J.F.T. (1957) – On the keepability of cut flowers meded. Landbouwhogesch. 57(9), 1-62. BARSOTTO P., STURLA A., TRIONE S. (2008) – La floricoltura ligure: un analisi del settore del contesto attraverso la RICA. INEA pp. 113. CAMPBELL S.J., OGLE H. J. JOYCE, D.C. (2000) – Glycerol uptake preserves cut juvenile foliage of Eucalyptus cinerea. Australian Journal of Experimental Agriculture. 40(3), 483-492. DELAPORTE K.L., KLIEBER A., SEDGLEY M. (2000) – Postharvest vase life of two flowering Eucalyptus species. Postarvest Biology and Tesnology 19, 181-186. DELAPORTE K.L., KLIEBER A., SEDGLEY M. 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