The Red Pitaya, A New Exotic Fruit
The Red Pitaya, also called Strawberry Pear (Hylocereus undatus
Britt. and Rose) is a spiny tropical cactus originating in Central
America. It is cultivated in Nicaragua over a 150-hectare area on the
west and south slopes of the Mount Santiago volcano, about 20km from
Managua.
The fruit of the cactus is very attractive, with a
distinctive appearance and a vivid red colour. In recent times, several
consignments of this fruit have been exported to European countries.
The Fruit
The
pitaya bears a large fruit which is pink, red, or mauve in colour,
weighing around 250-350gm. The oval or rounded fruits have skins on
which strongly or weakly expressed scaly markings appear; these scales
correspond to the bracts of the flower. The flesh is dark red,
approaching mauve in colour, and contains numerous tiny shining black
seeds. Between the flesh and the skin there is a thin mucilaginous
layer.
The fruit is pulped for juice, used in ice cream, or
added to fruit salads. It does not have a strong taste, so lime juice
is often added to bring out the flavour.
According to Incer
[1959], the fruit is useful in combatting anaemia. In Colombia, Becerra
[1986] has noted that the pitaya (in this instance the yellow-fruited
variety, Cereus triangularis Haw.) contains the heart tonic captine;
whether this is also true of the Red Pitaya of Nicaragua is yet to be
determined.
The skin and the mucilaginous layer together make up
30-50% of the fruit weight, with this proportion varying with variety
and fruit size. A Nicaraguan study [Campos-Hugueney, 1986] has shown
that the pulp contains 84.4% water, 0.4% fats, 1.4% protein, 11.8%
carbohydrates, 1.4% cellulose, and 0.6% ash. It also detected the
presence of vitamin C (8mg/100g) and traces of vitamin A. The pulp
colour is due to anthocyanins.
Ecology
The
pitaya is a species of dry tropical climates. Its heat requirements are
high - the average temperature should be 21-29°C, while the maximum
can go to 38-40°C without the plant suffering any apparent harm.
Water requirements are modest (600-1300mm), with alternating wet and
dry seasons. Excessive rain leads to flower drop and rotting of
immature fruit. For good production, the plants need a lot of sunshine.
The
pitaya is a species which has been shown to have resistance to the
sulphurous gases emitted by the Mount Santiago volcano. This explains
the location of its present area of production, as growers in that area
have hardly any other feasible alternative apart from pineapples.
Plant Development
The
plant grows in the form of jointed stem segments. Each segment can
reach a length of 2m and be 3-7 cm across. Each segment has three, or
occasionally four, longitudinal ridges, along which lie small swellings
equipped with spines.
The segments easily form aerial roots,
which they use to attach themselves to supports. These can be living or
dead, such as trees, wooden or cement posts, stone walls, or volcanic
rocks. These roots can extend down to the soil to extract nutrients
from it.
The pitaya is found wild over most of Nicaragua. Seeds
are spread by birds, and may be found germinating high up in tall
trees, such as Pithecolobium saman, Enterolobium cyclocarpum, and
Crescentia cujete.
In cultivation, pitaya is propagated by stem
cuttings, put directly in place at the end of the dry season. Usually
three segments are placed around a living tree support; in current
plantings, these supports are on a 3 x 5 m grid.
The best living
posts are leguminous trees which root easily from large cuttings, such
as Erythrina species and Gliricidia sepium. Other species used include
Bursera simaruba, Spondias purpurea, Crescentia cujete, and Cordia
species. The living posts must be pruned regularly so that they do not
shade the pitayas too much.
Flowering
Flowering
is initiated at the end of the dry season, in April, and continues
through the wet season, to October. It seems to have a dependence on
day-length (photoperiodism); irrigating plants during the dry season
does not initiate flowering unless it is already close to the normal
flowering time.
Flowers appear individually on the lateral stem
ridges. They are large, perfumed, ivory white in colour, with a great
many stamens. They open at nightfall and close at daybreak, with each
flower lasting only one night.
Flowering in cultivated plants
goes according to well-defined cycles, with all the flowers of the same
plant, and all the plants of the same clone, developing according to
three phases. Phase 1 is the appearance and development of flower buds,
lasting 15-16 days; Phase 2 is flowering, lasting 3-5 days; and Phase 3
is the development and ripening of the fruit, which takes 30-35 days
from flowering.
Flowering may have barely ceased when the flower
buds of the following cycle appear. So it is possible to find flower
buds, young fruits, and almost ripe fruits on the same plant at any
given time.
Theoretically it would be possible to have 7-9
separate fruiting cycles during one wet season. In practice, 5 or 6
cycles occur, probably due to climatic or nutritional limitations.
Fruit drop in immature fruit is an important occurrence, but its cause
is not known.
Varieties
There
are no varieties in the proper sense, only clones which differ markedly
in such things as type of stem segment, colour and shape of fruits,
skin thickness, and scale expression. One clone is spineless. Other
plants differ in flowering season, some being late, others early. It
will be of interest to find out if these variations have a genetic
basis or are more due to environmental factors. In either case, these
variations offer the possible of extending the production season.
Growers have assigned descriptive names to some clones, such as 'rosa' (pink), 'mariposa' (butterfly), and 'orejona' (big-ears).
Cultural Requirements
During
the three years of first establishing a Pitaya plantation, it is
possible, and even desirable, to intercrop, as long as the low
intercrop does not compete with the pitaya cultivation. Kidney beans
are the commonest intercrop. In recent years, some growers have
interplanted with pineapples. These plants have the advantage of better
resistance to sulphurous gases from the volcano, and allow earlier
recovery of the initial investment. Whatever, it is desirable that the
pineapples be eliminated after two harvests.
No formal
fertilizer trials have been carried out. Growers will apply urea or a
complete fertilizer if this is economically worthwhile to them. Some
have applied fertilizer as a foliar spray - this can bring about
flowering several weeks earlier and reduce immature fruit drop.
Each
year, rotted support posts must be replaced and weak ones reinforced.
Maintaining the supports is one of the biggest costs to the grower.
Pruning
living posts is an ongoing cost in pitaya culture; a balance needs to
be maintained between growth of the living posts and that of the
pitaya, which must not be excessively shaded. The pitayas themselves
must also be trimmed to keep their volume down and permit movement
along the interrows.
Pitayas have only superficial roots, and so
are very vulnerable to damage if the soil is worked. In mature
plantations the recommendation is to avoid working the soil, and
control weeds with a herbicide instead.
Pests and Diseases
As
a cultivated plant locally selected from the wild, the pitaya is
subject to attack by numerous locally-evolved pests and diseases.
According to Urbina [1989], the most important problems are due to:
• The larva of a beetle, Cotinus mutabilis, which chews the stem segments and favours infestation by pathogenic fungi;
•
A winged insect, Leptoglossus zonatus, which sucks the sap of the stems
and fruits, leading to marks and deformations. This is also suspected
of transmitting fungal and bacterial diseases;
• Ants,
particularly leaf-cutting ants of the genus Atta, which can cause great
damage to fruits. The ants attack the scales and so the fruit skin,
weakening the fruit and rendering it liable to disease attack and skin
splitting when ripe;
• Often some stem segments show
symptoms of a watery rot, which may be limited to a single segment
without affecting those above and below. The segment later dries out,
leaving only the main veins. The problem is due to a bacterium,
Xanthomonas campestris;
• A fungus problem, called
'fish-eye', where a fungus of the genus Dothiorella causes brown
circular spots, 1-3mm across, to appear on the stems. When the
infection is severe, the spots can join up, and the surface available
for photosynthesis is greatly reduced.
Finally, mention should be made of damage caused to ripening fruits by birds, lizards, and rodents.
Yields and postharvest factors
The
first harvest can be expected 18 months after planting. Using local
measures, a yield of 300 dozen fruits can be expected per hectare in
the second year, equivalent to 0.8-1.0 t/ha. Yields increase
progressively up to 3000 dozen fruits (10-12 t/ha) by the fifth year,
which corresponds to the mature stage of establishment.
Each
clump of adult plants produces about a dozen fruits per cycle between
June and November, that is 5-6 dozen fruits per year. Production
records show a number of peaks, corresponding to the different
flowering cycles.
Fruits can be harvested once the colour of the
skin starts to change from green to red. They are then held in a shaded
spot which is sheltered from birds and rodents. The fruit should be cut
off with secateurs, since it has no real fruit stalk and if it is just
twisted off, this tears the fruit skin at the point of attachment and
makes it unsalable.
Preliminary studies on fruit keeping have shown that:
•
Fruits harvested green, two days before the expected colour change,
ripen normally at ambient temperatures (25-30°C) and have a keeping
life of 9-11 days;
• Fruits harvested at the colour change keep for 7-8 days;
•
Fruits harvested fully ripe, that is when the skin has become fully
red, remain good for eating for 5-6 days at ambient temperatures;
• Ripe fruits left on the plant keep for 8 days after the colour change, provided they are not eaten by birds.
Fruits
kept in cool storage (10-12°C) for a week continue to ripen, but
more slowly, and colouration is less intense. After removal from cool
conditions, ripening is accelerated.
After four days, fruits
harvested just ripe begin to rot. Those harvested at colour change or
green remain presentable for 5-7 days.
So cool storage slows
ripening of green or turning fruit, and can prolong its life. While a
little skin colouration may be sacrificed, the pulp colour does not
seem to be affected.
The influence on lifetime of higher and lower temperatures, and of different clones, remains to be evaluated.
References
Becerra, O.A. (1986): El cultivo de la pitaya. Federación Nacional de Cafeteros de Colombia.
Campos-Hugueney, L. et al. (1986): Advances en la tecnología de la pitahaya (Hylocereus undatus). Bol. Tecn. LABAL, Nicaragua.
Incer,
B.J. (1959): Carácteres geobotánicos y flora medicinal de
la región de Chontales. Thesis, UNAN, León, Nicaragua.
Villegas, Marcelo (1990): Tropical Bamboo. Rizzoli, New York.
Sarmiento Gomez, Eduardo (1989): Frutas en Colombia. 2 ed. Ediciones Cultural, Bogotá
Urbina,
B.P. (1989): Caracterización a nivel de campo y laboratorio de
las plagas y enfermedades más importantes del cultivo de la
pitahaya en la IV region (masyay) Nicaragua. Unpublished thesis, ICSA,
Nicaragua.
[Based on an article La pitahaya rouge, un nouveau
fruit exotique, published in the magazine Fruits, Vol. 45, No.2, 1990.
Translation from French: David Noël] WANATCA Yearbook 1993.
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