The Pitaya or
Dragon Fruit
Introduction
Plants
in the cactus family, Cactaceae, originated in North, Central, and
South America. They are widely distributed, from coastal
areas, to
high mountains, and in tropical rainforests. Their appearance
is
just as variable, from thimble-size species, to enormous column
species, and the epiphytic (climbing) species.
The cactus family are highly adaptable
to a new environment.
The plants are able to tolerate
drought, heat, poor soil, and cold. The
modification of the stem for water storage, the reduction or
absence of leaves, the waxy surfaces, and night-time opening of the
tissues for carbon dioxide uptake (the CAM process), enable the plants
to tolerate harsh conditions. Terms used to describe plants
with
adaptations
include xerophyte and succulent. These adaptations to survive dry, hot
conditions, apply to the above-ground plant. The roots are
non-succulent and require small amounts of water and cooler
temperatures. Cacti will not tolerate saline or water-logged
conditions, nor will they grow where there is an absence of plant life.
In
their native lands, the plants were used for many purposes, but one of
major importance is the fruit as a food source. Fruit was
collected from naturally established stands. Later, cuttings were taken
from highly productive plants and grown around houses. A
similar
process is now in place in several countries around the world to
establish plantations of cacti with edible fruit, from column, shrubby
and climbing types. Epiphytic or climbing cacti use their
adventitious roots from the stems to cling to rocks and trees for
support. These roots do not feed from the host
plant. The
aerial roots collect water and nutrients from their surroundings,
enabling the plant to survive if the base is severed. This
feature
also allows the plants to be successfully grown from cuttings.
Hylocereus
undatus (Haworth)
Britt & Rose, a climbing cactus thought to be from the tropical
rain-forests of Central and northern South America, is one species that
has been used as a food source. It has already received
world-wide
recognition as an ornamental plant for the large, scented,
night-blooming flowers. Its fame is now spreading throughout
the
world for its fruit, especially in Israel, Vietnam, and Australia.
Other climbing cactus species grown for
the
edible
fruit
include
Hylocereus polyrhizus
and
Selenicereus megalanthus. H. polyrhizus has red
skin and red flesh dotted with edible black seeds,
while S. megalanthus,
the pitaya amarillo or yellow pitaya,
has yellow
skin and clear to
white flesh
containing edible black seeds. Columnar cacti, such as Cereus peruvianus -
the apple cactus, and the shrubby Opuntia
species - the cactus (prickly) pears, are also grown for their edible
fruit. The Opuntia
species are also well known due to their noxious weed status.
Plants spread and establish rapidly from seeds and vegetative
pieces. The potential for Hylocereus
to become a weed is unknown at this stage.
Growing areas
In
Mexico, Guatemala, and northern South America, the cactus fruits are
known as pitaya, pitahaya, pitajaya, pitaya roja, and pitahaya de
Cardón. In Israel, the name pitaya has been adopted. In Vietnam, the
fruit is called Dragon Fruit or Thanh Long. The plants grow
naturally in Mexico, Central and South America and are also planted in
backyards. Orchards are now established to provide fruit for
the
local and export markets in North America and Europe.
Hylocereus
undatus
is not able to tolerate the intense sun-light in
Israel. Plantations are established in shadehouses on metal
trellis systems to provide fruit to the local and export markets in
Europe.
About one hundred years ago, the French brought
H. undatus into Vietnam,
where it was grown exclusively for
the
King. Later, it became popular with the wealthy families
throughout the country. More
recently, it has been established
as a backyard and
orchard plant, providing fruit to the local and export markets in South
East Asia and Europe.
Fruit appeal
So
successful is the fruit in Vietnam, that at times it is the major
export item, and can fetch higher prices than durian - the' King of
Fruits' in South East Asia. Formerly uncultivated, marginal
lands
are used to establish H.
undatus
orchards. The plants are grown on concrete or wooden posts,
trees
and
fences, for support. The branches are encouraged to hang
down to promote flowering and fruitset. Water and fertiliser
requirements may be lower when compared to other tropical fruit species
grown in these areas.
The attractive colours in the fruit encourage
people to buy. The bright red or pink skin glows, the green
scales
enhance the red skin colour, and the brilliant white flesh looks even
more enticing dotted with the tiny, edible, black seeds. The
fruit
is considered a gourmets' delight, creating a spectacular centrepiece
on any table.
Pitaya fruit
Uses for the fruit
H. undatus
fruit is highly appreciated when served chilled and cut in half to
reveal the attractive colours. The flesh and seeds are scooped
out
with a spoon, much like a kiwi fruit.The flesh is firm and
crisp,
with a delicately sweet and lingering flavour. The juicy flesh
can
also be mixed with milk or sugar, used in marmalades, jellies, ices and
soft drinks.
Flowering and
fruiting
In warm climates, the dry season is when active growth slows or
stops. H.
undatus flowers are self compatible, producing
fruit with one species, but cross-pollination with other Hylocereus species
can produce larger fruit. H.
undatus
is a long-day plant, requiring longer day lengths to induce flowering.
In the Northern Hemisphere, the main fruiting season occurs between May
to October. Recent observations suggest the season in Darwin
may
extend from October to April.
Buds
are contained in aureoles along the three-ribbed stem and emerge in the summer months. Once
emerged, the buds then form into branches or flowers. The
scented,
white, night-blooming flowers attract bats and moths. Bees and other
insects visit the flowers before dusk as the petals open, and after
dawn as the flowers begin to close. Ten days after opening,
fruitset is visible. Fruit development is
rapid. After a
further 25 days, the fruit is ready to be harvested. Fruit can
be
left on the stem up to 15 days at this stage.
The average fruit
weight is 350 grams and this increases with the number of seeds
present. The flowers and fruit can be thinned to 1-2 fruit per
branch, to produce fruit of an even size and quality for the export
market. An unripe fruit contains mucilage, a sticky substance,
which makes the fruit unappealing. Fruit is cut from the stem
at
the full-colour stage and packed for the markets. At the
full colour stage, the skin becomes pink-red and the scales
remain
green. The fruit is non-climacteric, having the best flavour,
soluble sugar level and acidity when harvested at the full colour stage.
From
the information gathered on pitaya, the stored fruit have thinner skin
as water moves from the skin to the flesh, higher sugar levels but less
flavour than freshly harvested fruit, and may develop
rots. The
yellow pitaya (S.
megalanthus)
can be stored for four weeks at 10°C, and a week or more at
20°C. The relative humidity for both temperatures is 60 -
70%. Caution is needed when using these suggestions until data
is
available for H. undatus. In
Vietnam, a second fruiting season is possible using lights to extend
the daylength or potassium nitrate to induce flowering. Induction
commences 70 days before the expected harvest although less fruit is
produced from flower induction.
Orchard
management
Seedlings
are slow growing, making them unfavourable for propagation. Healthy,
green cuttings are preferred for rapid propagation. The
cutting
should be half a metre in length for successful
establishment. The
cutting is cured by storing in a dry place for a week before potting
into a free-draining mix. Cuttings need
to be
shaded and require minimal water and fertiliser before the roots
develop. Once the roots have developed, the plants can be
sun-hardened and planted into a mounded area. Plants
should be established on well-drained beds, up to 300
millimetres high, three metres apart within
a
row and four meters between rows, depending on the size of orchard
equipment. Concrete or wooden posts can be used as support,
with a
frame on top to train the branches. One to four plants can be
used
for each post depending on post size. A single leader stem is
grown up the post, with side branches removed, until the top of the
post is reached. Branches then need to hang down to flower and
fruit, and training is easier at midday when the branches are
soft. The majority of roots are found in the top 15-30
centimeters
of soil and irrigation is required to ensure the soil does not dry out
completely. Wet and dry periods during fruit development may
lead
to splits in the fruit. Irrigation is used to maintain water levels in
the soil during fruit development to prevent splits. Thick
mulch
placed on the mound, but away from the stem, will also slow water loss.
Many
of the fruiting cacti grow naturally in areas with high minerals, lime
and decaying organic matter. A balanced NPK fertiliser,
organic
fertiliser, lime, and foliar fertiliser during fruit growth, are
required by H. undatus. Fertiliser
is included in the planting hole and then applied after the first
month. A three month fertiliser program continues after this,
with
a once a year organic application and liming. Fertiliser can
be
applied as granules or through the irrigation. Nitrogen is
required during vegetative growth, but is normally reduced during the
resting and pre-flowering stages. Urea sprays, at 3-5%, can be
used to encourage vegetative growth, with micro elements added if
required. Pruning the tips allows easy access through the
orchard
and is used for flower and fruit thinning. An open,
manageable,
and productive canopy is maintained by thinning the
branches. A
plant in the first year should have 30 branches, increasing to 130
branches in the fourth year. After harvest, the plant is pruned to a
maximum number of 50 main branches, with 1-2 secondary branches on a
main branch. Tertiary and quaternary branches should be
removed.
Cacti
may be attacked by a range of pests that should be monitored and
controlled with the recommended sprays and baits. Pests can include
mites, thrips, ants, scale insects, mealy bugs, beetles, slugs, borers,
nematodes, fruit flies, and mice. Some, or all of these, may
be
present on H. undatus. Diseases
from fungi and bacteria can occur if injury or wet conditions are
present. Contact Departmental officers from the Resource Protection
Division for suitable control methods.
The future
H. undatus
has a niche market in Australia at present. Prices are
dependent
on the demand for the fruit. The ease of establishment and
rapid
growth may quickly lead to an over supply in the market. The
export potential for H.
undatus from Australia is unknown at this stage.
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