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Ornamental

 
                 
 
 
Use of Camellia
Fact
Financial importance
Plant care
Propagation
Camellia protection
Disorders
Insect pests

Diseases

 
 
 

Significance of Camellias

All of the 267 species recorded within the genus Camellia originated from Asia except C. lanceolata , which is a native of the Philippines and Indonesia. In China, Camellias have been used in the last three centuries as ornamental plants, and to provide food from fermented young leaves, cosmetics, culinary and industrial oils, high grade charcoal for fuel, and tea. In Japan, green tea made from leaves of Camellia sinensis that have been steamed, rolling and dried, is an integral component of the tea ceremony. Besides its cultural significance, Camellias have been used in Japan in textiles, ceramics, brewing, cooking, household utensils, tools, printing, crafts, farming, fuel, medicine and foodstuffs and cosmetics. Camellia plants have also been used as roadside trees and fences. Camellia is the symbolic flower in more than 30 Japanese communities.

Camellias were introduced into Europe in the 17th century with the beverage tea, and later became treasured as ornamental flowering plant. They were introduced into the United States in 1774 to establish tea growing, but this venture failed. Ornamental Camellias did not became established in the United States until enthusiasts began seeking perfect blooms around the 1940s, many years after the first flowering cultivar was imported to New Jersey in 1797. Ornamental Camellias were introduced from England to Australia in 1826. They were introduced into New Zealand soon after by missionaries and others from Australia, and from England by British settlers. Some of the oldest Camellia trees in New Zealand are found in Akaroa, which was established in 1840 by French colonists.

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Use of Camellia

Some species of Camellia are still grown for their economic value. The leaves of C. sinensis L. var. sinensis and C. sinensis var. assamica are used to make tea. Crushed seeds of some species such as C. oleifera , C. chekiangoleosa , C. reticulata , C. grijsii , C. vietnamensis , C. crapnelliana and C. gauchowensis are cultivated for production of high quality oils. The oil is used in cosmetics and for cooking, while other Camellia products are used by pharmaceutical and manufacturing industries. Production of tea oil from C. oleifera is currently under investigation in Georgia, US. The oil is used in cooking and in the cosmetic industry, with process residues being considered for livestock feed and insecticide formulations.

Green tea recipe

Camellia sinensis , the tea plant, is used to make the tea we drink. There are many different processes used to dry the leaves for making the beverage. There are also many varieties of C. sinensis used to make tea, with villages in China having their own strain of tea plants with different qualities. There is even a tea variety developed in China that does not have caffeine.

Try this Chinese recipe for green tea. The tea is reported to be delicious, very smooth and not bitter.

  1. Pick young shoots with 2-3 leaves from C. sinensis .
  2. Roll several shoots between your hands until the leaves darken and become crinkled. Bruising the leaves allows the fermentation process to begin. Do not break the leaves into pieces.
  3. Place thin layers of leaves on a tray in a shady location and allow the fermentation process to occur over 2-3 days.
  4. Dry the leaves in an oven at 106°C (250°F) for 20 minutes. This step is necessary to remove all the water in the leaves and stop the fermentation process.
  5. Store the tea in an airtight container, or use immediately.

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Ornamentals

Most Camellias are now grown for their ornamental value. Camellia flowers have been selected for centuries to produce a wide range of colours, flower forms (single, semi-double peony, anemone, rose-form double and formal double), and sizes (1-23 cm) (Figure 1). The most popular ornamental species of Camellia are C. sasanqua , which flowers in autumn and winter, and C. japonica L. and C. reticulata, which flower in winter and spring. Inter-specific hybridisation has led to around 5600 hybrids being registered worldwide.

Figure 1 : Flowers of Camellia japonica cultivars (clockwise from top left) Little Michael, Nuccio's Pearl, Wilhelmina and San Dimas.

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Fact

There are 32,000 entries of Camellia cultivars in the International Register, but many of these are invalid names - synonyms, duplications, etc. Many entries represent extinct cultivars, where the names have been extracted from books produced in Japan and China hundreds of years ago, as well as in Europe in the 19th century. So the number of valid entries is possibly around 15,000.

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Financial importance

Camellias represent an important part of the nursery trade in New Zealand. The Camellia industry generates about $2-4 million worth of domestic sales and $0.4 million in export sales annually. Most of the plants are used for amenity or ornamental purposes.

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Plant care

 

Choice of location

A garden shaded by deciduous trees provides ideal conditions, including good sunlight with high humidity, temperatures below 15°C in winter, and shade in summer. Soils should be rich in humus, porous, and slightly acidic (pH 5.5). Camellias also survive well in pots.

Fertilisers

To encourage flowering in potted plants, use a general potting mix consisting of 500 g of 12-14 month release Osmocote Plus (15% N, 3.5% P, 9.1% K, 1.2% Mg, plus traces of B, Cu, Fe, Mn, Mo and Zn) in 200 L of bark and 50 L of sand. Re-pot every two years. An alternative soil mix is one-third each of decomposed compost, garden soil and moss peat.

If the potting mix has no fertiliser in it, add fertiliser weekly to each pot during spring, immediately before flowering, ceasing application by early summer. Use 2 g of an ericaceous fertiliser (one suitable for azaleas or rhododendrons) mixed in 1 L water per plant.

Camellias in the garden will normally thrive without fertiliser. However, they will respond with improved growth and flower vigour to an ericaceous fertiliser applied once in early spring prior to flowering. Apply fertiliser to soil under the drip line of each plant at a rate of half that recommended on the label. Water the fertiliser into the soil. Avoid using lime, which will increase the pH and create a basic soil.

Watering

Camellias can die in dry soils. Water the soil around Camellias regularly but avoid creating waterlogged conditions. Soils do not require watering if they feel moist to the touch.

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Pruning

Pruning of 1-3 year-old Camellias encourages earlier and better branching. Cut the main shoot of 1 year-old bushes back to a length of 10-15 cm to encourage outward branching.

Prune older bushes to the space available, and the second batch of new shoots produced by some cultivars, which may cause an undesirable shape in the bush.

Prune immediately after the new shoots have started forming, after flowering has finished. Cut the selected branch 2 cm above a set of leaves.

Misshapen bushes can be trimmed to the trunk using a technique descriptively called 'Hatracking' (Figure 2). The bush will regenerate and produce flowers in the next flowering season.


Figure 2 : Hatracking of Camellia bushes at the Wellington Botanic Gardens.

 

 

Propagation

Camellias can be propagated vegetatively from a single Camellia cultivar, and generatively from two Camellia cultivars or species, by different methods.

Vegetative propagation

 

Layering

Seedlings are propagated from a low-hanging downward-pointing branch of a Camellia bush that is more than two years old. Remove all leaves and shoots of the branch except for a few leaves at the tip. Cut a small incision near the tip of the branch, and train the branch down to the ground or into a pot containing standard potting compost. Secure the tip in the soil with a peg, heap peaty soil over it and keep it moist. After two years, roots will have formed from the incision, and the shoot tip can be separated from the mother bush and transplanted.

Cuttings

With this most successful propagation method, new plants should flower after one year. Take cuttings in February. From the mother plant, select a top shoot that has at least two leaves and no buds, and is 15 cm long and olive green (signifying the optimum level of maturity). Cut the stem diagonally 2 cm below the lowest leaf using a sharp knife that has been sterilised in alcohol. Dip the cut surface into a rooting powder. Push the cutting 2 cm deep into sterilised potting mix (heated in a fan oven at 120°C for 40 minutes) in an 8 cm diameter pot. Cover the pot with a stiff plastic bag and seal the bag to the pot with string. Incubate under shade at 25°C until roots form (8-12 weeks). Then remove the bag, and incubate at 16°C for a further four months when the seedling can be re-potted in Camellia soil.

Root stimulation from stems

During the growth phase (after flowering), remove the leaves on a 30 cm length of stem on a selected mother plant. Make two incisions 2 cm apart around the circumference of the stem, and peel off the bark skin. Tie the end of a section of a transparent cylindrical plastic bag below the scar. Fill the bag with moist moss peat. Then tie the bag around the stem above the incision. Once roots appear inside the peat-filled bag, separate the shoot with its new roots from the mother bush, and plant it in an 8 cm diameter pot filled with Camellia soil.

Grafting

This method is suitable for cultivars that do not produce roots readily. Camellia japonica and C. sasanqua are good stock species. Cut the base of the scion of the cultivar to be propagated into a wedge, and insert the wedge into a slot cut into the stock. Secure the scion with grafting tape or cotton wound tightly around the join. The two pieces will fuse together within eight weeks.

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Generative propagation

Raise your own Camellia by crossing cultivars of the same or compatible Camellia species. Transfer ripe pollen grains from the anther of a flower or number of flowers of one Camellia bush to a ripe stigma (recognised as receptive by secretion of a mucus). Cover the recipient flower with gauze until fertilisation has occurred (recognised by petal drop) to avoid inadvertent pollination from other genotypes. Under favourable climatic conditions, a woody seed capsule the size of a walnut will have formed by autumn. It will open naturally to release up to six blackish-brown seeds.

Test the resulting seeds for viability by placing them in a bowl of water. Seeds that sink to the bottom after 10 minutes are viable. Those that float are sterile and incapable of germination.

Sowing seeds

Press three seeds per pot about 25 mm deep into potting mix contained in a 10 cm diameter pot. Cover with peat, and water. Place a transparent plastic bag over the pot and incubate at about 20°C. Remove the bag after the seedling develops two leaves (3-5 weeks). Prick out each seedling once it has grown a total of four leaves, into an individual pot containing Camellia soil. Re-pot as necessary. Flowering should occur 3-5 years after sowing.

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Camellia protection

In New Zealand, strongly growing Camellia bushes are generally free from invertebrate pests and diseases. However, Camellias can be susceptible to a number of disorders, insect pests and fungal pathogens present in New Zealand.

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Disorders

Physiological disorders result from climatic changes, nutritional imbalance or inadequate drainage, and can usually be rectified by changing the environmental conditions. Algae and lichen may grow on leaves in shady humid conditions. They have no effect on the health of the plant but can be controlled with a spray of copper oxychloride. Camellia cultivars with white or pale pink flowers are more delicate than cultivars with darker-coloured flowers and may develop brown petals from exposure to sun or wind. Shading from extremes of weather and careful pruning to prevent blooms from rubbing against other parts of the plant are recommended. Extreme frost or changes in temperature can induce buds to drop before flowering. Transferring the plant to a more sheltered part of the garden could solve this problem.

Chlorosis of the leaves could be due to natural senescence, a genetic condition, or it may be caused by extended dry periods resulting in dehydration, or an excess of water with poor drainage. Chlorosis caused by alkaline soils, which prevent iron and other nutrients being available in a soluble form, can be ameliorated by applying acid fertilisers, compost, and iron chelate or iron sulphate. Yellowing between green veins in the leaves can indicate lack of iron or magnesium, readily corrected by application of sulphate of iron or magnesium sulphate. Corky scabs on the undersides of leaves can result from plants absorbing more water through the roots than the leaves can transpire (oedema), and can occur through over-watering. It can also occur in Camellias with a large root mass and little foliage.

Bronze patches on leaves can occur in some cultivars exposed to hot sunny conditions as a result of sunburn. Shade solves the problem. Potassium deficiency can result in brown patches on leaves and can be corrected with potassic superphosphate. An excessive build-up of salts in the soil can result in edges of leaves turning brown, and is usually corrected by thorough watering to wash the salts from the immediate root zone.

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Insect pests

Sucking insects including scale and aphids, which may affect the vigour of Camellia plants less than 5 years old, require treatment with insecticides. The scale insect Pulvinaria floccifera can severely affect young bushes. They can be effectively controlled by spraying the bushes with Attack ® (a mix of permethrin, primiphos-methyl and hydrocarbon liquid) at 1 mL/L water until run-off. Aphids can be controlled easily with an readily available aphicide from your garden shop. These insects secrete sugars that black sooty moulds then feed on. Controlling these insects will also stop new mould growing on the leaves, but the old mould may require wiping off to remove the unsightly blemish.

Beetles of grass grub Costelytra zealandica and bronze beetle Eucolaspis brunnea , and larvae of case moth Liothula omnivorous , chew the leaves of Camellia plants, but they rarely affect the vigour of mature Camellia plants and have no effect on the flowers.

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Diseases

 

Viruses

Viruses can infect Camellias, but their effect is usually minor and aesthetic. Viruses can cause irregular blotches of white on coloured flowers, and irregular blotches of yellow or pale colour on the foliage. A virus causes ringspot, identified by faint green rings in young leaves that turn bright green with dark edges within yellowing leaves as they mature. Viruses can be introduced by grafting on to infected stock, and by using scions from infected plants as cuttings. Some breeders do this on purpose to create a variegated leaf in a new line of Camellias.

Fungi

Fungal diseases of Camellia plants are more serious. Dieback caused by the fungus Glomerella cingulata can be lethal to Camellias. Symptoms include sudden death and wilting of young shoots, followed by the dead leaves holding on to the shoot, and dying of tissue and growth of a canker, which continues to enlarge, extracting water and nutrients causing yellowing of leaves, loss of foliage and dieback of twigs and branches. The wind-borne fungus Exobasidium spp. affects young leaves at the ends of branches, causing them to become light green to white, or deep pink to red. Phytophthora cinnamomi is the main fungi of several species that cause root rot. Root rot disease is common in waterlogged non-aerobic soils. Symptoms are expressed in summer, when leaves become yellow and die, and branches wilt and die back from the tip until the whole plant dies. Roots of an affected plant will be dark brown and brittle, and contain few white fibrous roots essential for a healthy plant.

Two fungal diseases of flowers are of concern because of the importance of Camellias for their flowers. Botrytis cinerea causes botrytis flower blight or grey mould, characterised by water-soaked brown spots on the petals. The spots spread fast to form tan to grey-brown blotches associated with the blighting and ecay of blooms. Colours on diseased flower petals quickly fade as the flower withers into a brown-grey wrinkled mass. The disease is prevalent when relative humidity exceeds the threshold of 93% for when botrytis spores infect the petals. Consequently, the disease can be a problem in glasshouse-grown Camellias. The other flower disease is Camellia flower blight, otherwise known as Camellia petal blight.

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Camellia flower blight

Since Camellias are most commonly grown for their attractive flowers, the most important disease affecting Camellias is Camellia flower blight, as the premature browning and fall of infected flowers detract from their aesthetic value and can make blooms unfit for showing (Figure 3 ). Camellia flower blight is caused by the sclerotial-forming fungus Ciborinia Camelliae , and is specific to flowers of most species of Camellias. The pathogen does not affect Camellia bushes themselves.

Camellia blight was first identified in Japan in 1919 and first found in the United States in California in 1939, spreading to most states where Camellias are grown within the next 50 years. In New Zealand, the disease was first reported in Wellington in 1993. It is present throughout New Zealand in most regions north of Ashburton.

 

Figure 3 : Symptoms of Camellia blight, comparing healthy and blighted flowers on Camellia Gwenneth morey.

While the symptoms of flower blight are similar to those of Botrytis infection, with browning and premature dropping of flowers, the diseases are easily distinguishable from one another. With flower blight, the entire and intact whorl of petals (corolla) separates easily from the receptacle, leaving a characteristic grey ring of fungal hyphae at the point of separation (Figure 4). With Botrytis , the petals come away separately, with no sign of grey fungal growth on the broken surfaces.

 
Figure 4: Early C. Camelliae infection in a Camellia flower (left), and advanced flower infection (right) showing growth of mycelium at the base, which eventually will develop into sclerotia in fallen flowers. Sclerotia of assorted sizes (bottom) can be found at the base of infected bushes.

 

The pathogen has a simple life cycle (Figure 5). Wind-borne spores arising in late winter and spring from the apothecia of soil-borne sclerotia infect the flowers of Camellias, and develop within the fallen flower to form new sclerotia. These produce apothecia in subsequent years.

Figure 5 : Lifecycle of Ciborinia camelliae .

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Current control options

Current control strategies are aimed at interrupting the lifecycle of the pathogen by preventing formation of sclerotia or apothecia, thereby preventing the release of ascospores, or by preventing infection of flowers on Camellia bushes.

Limiting its spread

The spread of the disease from an endemic area, and its introduction into new locations could be restricted by only transporting Camellia plants that are free of flowers, and as bare-rooted cuttings or scions. These measures aim to prevent old sclerotia in the soil or potential sclerotia in infected flowers from being transported along with the plant. It would be extremely effective if adopted, but home gardeners and many nurserymen often do not recognise that the pathogen is present when purchasing or transferring cuttings. Home gardeners who select their plants on the appearance of the flowers are also unlikely to purchase bare-root cuttings that are too young to flower. Once the disease is established in a region, a number of cultural and chemical methods can be used to prevent its development.

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Cultural control

The disease may be avoided by growing autumn-flowering species such as C. sasanqua , or cultivars that flower early in the season before apothecia are produced by the soil-borne sclerotia (mid-late July in New Zealand). While this approach might be effective, most growers of Camellias prefer to have Camellias flowering during the winter-spring period, when apothecial production is at its peak.

The fallen infected Camellia flowers may be raked up and burned to kill the developing sclerotia. A plastic sheet laid underneath flowering bushes makes collection of fallen flowers easier, and prevents apothecial development from sclerotia underneath. This approach would be highly effective if adopted universally, but is practised by only a few Camellia growers. Further, home gardeners do not usually burn the flowers, instead adopting the easier approach of discarding the flower debris in compost. As sclerotia may survive composting, council or private green-waste composting schemes can contribute to the spread of the disease.

Moisture levels on the ground where the sclerotia fall can be reduced, thereby depriving the sclerotia of moist conditions for subsequent development. This can be achieved by trimming the lower Camellia branches to about 0.5 m above ground, raking off loose-leaf litter and weeds to expose bare soil, or by covering the exposed ground with either black polythene or 75-100 mm thick pine needles. Adding ground cover could also be effective in smothering the soil-borne sclerotia and suppressing apothecial production from sclerotia underneath. However, these methods would have limited control of apothecia produced by sclerotia developing in flowers that fall after the ground cover has been applied. The apothecia could still form in wet seasons or after periods of rain.

Fungicides can be applied to soil under Camellia bushes to prevent production of apothecia by sclerotia, or they can be sprayed on to the bushes during flowering to protect blooms from infection by ascospores. Alternatively, cut blooms can be dipped into fungicide solutions prior to display at flower shows.

Application of fungicides to soil immediately prior to apothecial production has generally given effective control of apothecia. Alto ® 100SL (100 g/L cyproconazole) or Shirlan ® 500SC (500 g/L fluazinam) sprayed on to infested soil at 4 L/ha in 1000 L water/ha in early August, and reapplied 3-4 weeks later, can be effective in preventing production of apothecia during August to November. No fungicides are registered in New Zealand for use against C. camelliae , so the risk in controlling the pathogen is borne by the user.

Many foliar-applied fungicide sprays have been evaluated for protection of flowers against infection by ascospores, but generally they have not been successful in controlling the disease. For any degree of effective protection, the fungicides needed to be applied repeatedly during flowering. Bayleton ® 5 DF (50 g/kg triadimefon), applied at 1 g/L water to Camellia bushes weekly during flowering, only reduced numbers of blighted flowers by 31–77% in every season over six years in the United States. In New Zealand, Camellia bushes sprayed fortnightly until run-off with either Alto ® 100SL at 0.15 mL/L or Shirlan ® at 1.0 mL/L water, both containing a surfactant to help spread the fungicides during the 8 weeks of flowering, had disease levels similar to that of the untreated control (17%).

Dipping Camellia blooms into fungicide solutions has been shown to be effective in preventing infection of cut flowers. Healthy Camellia blooms dipped into a solution containing Cereous 250EC (250 g/L triadimenol) at 2.0 mL/L water, or Bayleton 5DF (50 g/kg triadimefon) at 4.0 mL/L water plus a few drops of washing up detergent, for 5 min 1–7 days prior to showing, can effectively delay the onset of the disease.

However, none of these strategies are sufficiently effective or practical for ready adoption by Camellia growers.

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Potential for biological control

A strategy for integrated biocontrol of Camellia flower blight was developed in a PhD project at Lincoln University. Two approaches were examined. One approach was to protect Camellia flowers against wind-borne spores arising from the sexual fruiting bodies by either stimulating the plant's natural defence systems or spraying naturally occurring microbes on to the flowers, but this approach was only partially successful. Although isolates of naturally occurring leaf-surface microbes such as Bacillus , Pseudomonas , Aureobasidium and Cladosporium spp. provided almost complete protection against Camellia blight in petal assays (Figure 6), they did not prevent symptoms on whole flowers on Camellia bushes, even after repeated applications with or without additives that were added to the formulation to aid spread of the antagonists over the flowers. It appears that the microbes were not able to colonise the burgeoning blooms in competition with other microbes in sufficient numbers to provide protection against infection.

   
Figure 6: Bio-protection of Camellia blight.

The other approach was to attack the soil-borne sclerotia with naturally occurring microbes and soil amendments, and thereby prevent apothecial production. Screens of 400 candidate microorganisms isolated from sclerotial baits and decaying sclerotia (Figure 7), two isolates of Trichoderma and an isolate of Fusarium lateritium reduced the number of viable sclerotia by 38-50%. This indicated that moderately parasitic micro-antagonists were present in soil under Camellia bushes.


Figure 7 : Ciborinia camelliae mycelium growing from healthy sclerotia (top left), and species of Trichoderma (top right) and other fungi (bottom) growing from parasitised sclerotia.

 

A range of soil treatments was also investigated in field trials in an attempt to reduce the viability and germination potential of over-wintering sclerotia. Nitrogenous fertilisers that contain cations have been shown by other researchers to stimulate microbial degradation of sclerotia of other pathogen species. Urea applied to soil at 10 g urea/m² (46 kg N/ha) in February and again in June reduced field populations of C. camelliae sclerotia by 64% in the following November. We think this reduction was due to stimulation of parasitic microbes.

The direct toxic effect of selected fertilisers on apothecial production was also tested. A single application of the fertiliser calcium cyanamide at 500-1000 kg/ha to soil under Camellia bushes immediately before flowering (July-August), was found to give complete suppression of apothecial production. This treatment could be used for short-term control of the disease. Calcium cyanamide decomposes naturally in the soil to urea, and so this may also aid in the reduction of sclerotia. Potassium bicarbonate and ammonium bicarbonate gave partial suppression (76-87%) of apothecia at the 300 kg/ha rate tested in the trial, and presumably could be more effective at higher rates.

Tree mulches can also stimulate parasitic microbes in the soil. Covering soil under Camellia bushes with 100 mm thick mulches from trees such as pine, gum, and manuka, for 9 months resulted in total suppression of apothecia and a 77% reduction in the population density of soil-borne sclerotia, compared to bare soil. The different species of tree mulches had a similar effect on reducing numbers of sclerotia. However, the tree mulches had no effect on the new generation of C. camelliae sclerotia developing in fallen flowers, which would produce fruiting bodies in subsequent years.

The successful control strategies developed in this study could be integrated into a programme for effective control of Camellia blight. Urea applied at 20 g/m² (200 kg/ha) to soil beneath Camellia bushes followed by a 100 mm thick layer of tree mulch should result in significant suppression of apothecia, thereby preventing infection of flowers, and resulting in a gradual decline in numbers of soil-borne sclerotia.

Acknowledgement

Thanks to Dr Vince Neall, President of the New Zealand Camellia Society, for critiquing this manuscript.

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