From Plant Resources of South-East Asia No 2: Edible fruits and nuts, PROSEA Foundation
by V. N. Villegas
Taxon
Carica papaya L
Protologue
Sp. Pl.: 1036 (1753).
Family
CARICACEAE
Chromosome Numbers
2n = 18
Vernacular Names
Papaya,
pawpaw, melon tree (En). Papayier, arbre de melon (Fr). Indonesia:
papaya, gedang (Sundanese), kates (Javanese). Malaysia: papaya, betek,
ketalah. Philippines: papaya, kapaya, lapaya. Burma: thimbaw. Cambodia:
lhong, doeum lahong. Laos: houng. Thailand: malakor (central), loko
(peninsular), ma kuai thet (northern). Vietnam: du du.
Origin and Geographic Distribution
The genus Carica L. is indigenous to tropical America and the papaya must have originated from natural hybridization involving Carica peltata
Hook. & Arn. From tropical America it was brought to the Caribbean
and South-East Asia during the Spanish exploration in the 16th Century.
It then spread rapidly to India, Oceania, Africa, and today it is
widely distributed throughout the tropical and warmer subtropical areas
of the world.
Uses
Ripe papaya is a favourite
breakfast and dessert fruit that is available year-round. It can be
used to make fruit salads, refreshing drinks, jam, jelly, marmalade,
candies and crystallized fruits. Green fruits are pickled or cooked as
vegetable. In Java, a sweetmeat is made from the flowers. Young leaves
are sometimes eaten. In some countries, seeds are used as vermifuge and
abortifacient. Carpaine, an alkaloid present in papaya, can be used as
a heart depressant, amoebicide and diuretic. In some countries papaya
is grown in sizeable plantations for the extraction of papain, a
proteolytic enzyme present in the latex, collected mainly from the
green fruit. Papain has varied uses in the beverage, food and
pharmaceutical industries: in chill-proofing beer, tenderizing meat,
drug preparations for digestive ailments and treatment of gangrenous
wounds. It is also used in bathing hides, degumming silk and softening
wool.
Production and International Trade
FAO
statistics for 1988 show a total world production of 3.68 million t.
Among the major producers are Brazil, Mexico, Indonesia, India and
Zaire. In the same year Asia contributed nearly 25% of the total papaya
production; within the region, Indonesia produced 270 000 t, the
Philippines 95 000 t, Malaysia and Papua New Guinea 12 000 t each; no
production data are available for Thailand. The Philippines exports a
modest amount of fresh papaya to Hong Kong and New Zealand. Malaysia
and Thailand export to Singapore.
The papaya fruit is delicate and
perishable and therefore lags far behind banana and pineapple in world
trade. Since so much of the fruit is grown in home gardens and does not
reach beyond local markets, official statistics probably greatly
underestimate the importance of the crop.
Properties
About 60% of the ripe fruit is edible. The approximate contents per 100
g edible portion are: water 86.6 g, protein 0.5 g, fat 0.3 g,
carbohydrates 12.1 g, fibre 0.7 g, ash 0.5 g, potassium 204 mg, calcium
34 mg, phosphorus 11 mg, iron 1 mg, sodium 3 mg, vitamin A 450 mg,
vitamin C 74 mg, thiamine 0.03 mg, niacin 0.5 mg, and riboflavin 0.04
mg. The energy value is 200 kJ/100 g. Major sugars are sucrose (48.3%),
glucose (29.8%) and fructose (21.9%).
Description
A
fast-growing tree-like herb, 2—10 m tall, usually unbranched, sometimes
branched due to injury, containing white latex in all parts. Stem
cylindrical, 10—30 cm in diameter, hollow, with prominent leaf scars
and spongy-fibrous tissue. Leaves spirally arranged, clustered near
apex of trunk; petiole up to 1 m long, hollow, greenish or
purplish-green; lamina orbicular, 25—75 cm in diameter, palmately and
deeply 7—11-lobed, glabrous, prominently veined, lobes deeply and
broadly toothed. Flowers male, female or hermaphrodite, axillary, found
on separate trees. Male flowers in panicles, 25—100 cm long, pendent,
sessile; calyx cup-shaped, small, 5-toothed; corolla trumpet-shaped,
2.5 cm long, with 5 spreading lobes, light yellow; stamens 10, in 2
whorls alternating with the petal lobes. Female flowers solitary or in
few-flowered cymes, 3.5—5 cm long; calyx cup-shaped, 3—4 mm long, with
5 narrow teeth, yellow-green; corolla of 5 almost free petals; petals
lanceolate, twisted, fleshy, yellow; ovary ovoid-oblong, 2—3 cm long,
with central cavity and numerous ovules; stigmas 5, fan-shaped,
sessile, deeply 5-cleft. Hermaphrodite flowers of 2 types: 'elongata'
type with flowers in short-peduncled clusters, partially united petals,
stamens 10 in 2 series, ovary elongate; 'pentandria' type, flowers
similar to female flowers but with 5 stamens. Intermediate flowers
occur as well, in which stamens become carpelloid producing irregular
fruits. Proportion and type of flowers produced may vary on same tree,
depending on age and environmental conditions. Fruit a fleshy berry,
ovoid-oblong to nearly spherical, or pyriform, cylindrical or grooved,
7—30 cm long, weighing up to 10 kg; skin thin, smooth, yellowish or
orange in ripe fruit; flesh yellowish to red-orange, edible, sweet with
mild and pleasant flavour; central cavity 5-angled. Seeds globose, 5 mm
in diameter, black or greyish, numerous, attached in 5 rows to interior
wall of ovary, enclosed in a gelatinous sarcotesta.
Ecology
Papaya
thrives in warm areas with adequate rainfall and a temperature range of
21—33°C. Its altitude range is similar to that of the banana, from sea
level to elevations at which frosts occur (often around 1600 m). Frost
can kill the plant, and cool and overcast weather delays fruit ripening
and depresses fruit quality. Fruit tastes much better when grown during
a warm sunny season, but yield can be very high at elevations around
1000 m, the altitude for papain production in East Africa in the 1960s.
Evenly distributed annual rainfall of 1200 mm is sufficient if water
conservation practices are employed. Plantations should be in sheltered
locations or surrounded by windbreaks; strong winds are detrimental,
particularly on soils which cannot make up for large transpiration
losses.
Papaya grows best in light, well-drained soils rich in
organic matter with soil pH of 6.0—6.5. It can tolerate any kind of
soil provided it is well-drained and not too dry. The roots are very
sensitive to waterlogging and even short periods of flooding can kill
the plants.
Propagation and planting
Papaya
is propagated by seed. Several techniques are known to produce cuttings
but these are too laborious compared with the use of seedlings. To
reproduce the desired characteristics it is best to get seeds through
controlled pollination. The sarcotesta enveloping the seed is removed
(because it inhibits germination) by rubbing the seed together against
a fine-meshed screen under running water. Thoroughly dried seeds stored
in air-tight containers remain viable for several years.
Seeds are
sown in small containers (tin cans, plastic bags or paper cups) at the
rate of 3—4 seeds per container. Use of sterilized soil minimizes
losses resulting from nematodes and damping-off fungi. Germination
takes 2—3 weeks. Another practice is to sow the seeds in sterilized
nursery beds and to prick out at the 2—3-leaf stage, transferring 3—4
seedlings to each container. Seedlings are transplanted about 2 months
after sowing when they reach the 3—4-leaf stage or 20 cm height,
preferably at the onset of the rainy season. During transplanting, care
should be exercised so as not to disturb the roots. Older seedlings
recover poorly after planting out. Papaya needs adequate drainage and
is often planted on mounds or ridges. Transplants must be watered
regularly until they are established.
Field spacings are in the
order of 3 m x 2 m to 2.50 m x 1.60 m, giving densities of 1667 and
2500 plants/ha respectively. The same densities are obtained by
planting in double rows spaced (3.25 + 1.75) m x 2.40 m or (2.50 +
1.50) m x 2 m. Thinning to one female or one hermaphrodite plant per
hill is done when the plants reach the flowering stage. In the absence
of hermaphrodite plants, 1 male plant per 25—100 female plants is
retained as pollinator.
Papaya grows best when planted in full
sunlight. However, it can be planted as an intercrop under coconut as
practised in the Philippines and other countries, or as a cash crop
between young fruit trees such as mango, citrus or rambutan.
Husbandry
Clean
cultivation is standard practice in South-East Asia. Weed control,
particularly around the small plants, is very important. If weeds are
only slashed — resulting in a grassy weed cover — the papaya plants
suffer severe competition. Experimental work shows a very good response
to mulching.
Irrigation is needed to minimize flower abortion and
maintain growth during the dry season. Watering once a week is
recommended if there are no data on crop water use, soil depth and
moisture retention.
Papaya is a fast-growing crop that requires
heavy fertilization. Nutrient removal is in the order of 1 kg N, 0.2 kg
P and 2.5 kg K per tonne fruit. In addition substantial quantities of
nutrients are tied up in the vegetative parts. The fertilizer should be
split between 2—4 applications per year; use of manure and mulch
steadies the release of nutrients. Calcium deficiency depresses growth
and fruit set and enhances fruit drop; liming (to a pH of about 6) is
the remedy. Fruit malformation, characterized by lumpiness or rough
bumps on the fruit, has been associated with boron deficiency; 20—40 g
borax per tree can alleviate the problem.
Diseases and Pests
Damping-off is caused by the soilborne fungi Phytophthora parasitica, P. palmivora and Pythium aphanidermatum.
Phytophthora also occurs in the orchard, infecting both the trunk and
the fruit. Good aeration, drainage, and hygiene are important to curb
these fungi in the orchard as well as in the nursery. It is advisable
not to replant papaya on the same land. Anthracnose, caused by Glomerella cingulata (imperfect form: Colletotrichum gloeosporioides),
primarily infects the fruit. The disease appears as small water-soaked
circular spots that enlarge into brown-black sunken lesions as the
fruit ripens. Fungicidal spray at 7—10-day intervals can control this
disease. A 20-minute hot water dip (45°C) reduces post-harvest decay.
Papaya
ringspot is a devastating virus disease that was detected in the
Philippines in 1982. It had earlier caused considerable losses in
Hawaii, Florida and Taiwan. Initially, the disease appears as oil
streaks on stems and petioles and as it progresses, mottling of leaves
becomes evident. Severely infected plants do not flower and die young.
The virus is transmitted by aphids. Control measures are planting in
isolation, removing and destroying infected plants, and using tolerant
cultivars. Cross-protection has been advocated, but this requires the
availability of a mild virus strain for inoculation of seedlings.
Mosaic is another virus disease transmitted by aphids, and bunchy top
is caused by a mycoplasma transmitted by a hopper.
Rootknot (Meloidogyne incognita) and reniform (Rotylenchulus reniformis)
nematodes infest papaya. Feeding nematodes cause root swellings or root
galls, resulting in yellowing and premature abscission of the leaves.
Since nematicide treatments are expensive, it is important to use clean
land, not replanting papaya in the same field.
The oriental fruit fly (Dacus dorsalis)
is a major concern of papaya- importing countries such as Japan and the
United States. The flies deposit their eggs in ripe fruit. Fruit should
be harvested at the mature green stage. Over-ripe and infested fruit
should be buried. Male flies can be baited by placing a cotton ball
dipped in methyl eugenol-malathion solution inside trap bottles
positioned every 25 m throughout the plantation.
Mites (Tetranychus kansawai and Brevipalpus californicus)
suck the plant sap, leading to poor plant growth and blemishes on the
fruit. Predatory mites generally provide adequate control, an
additional reason for restraint in the use of acaricides or
insecticides with miticidal action. Aphid (Aphis gossypii, Myzus persicae)
infestation weakens the plants and aphids also transmit virus diseases.
Removing alternative hosts and the presence of natural predators can
effectively reduce aphid populations. Spraying insecticide on the
undersides of the leaves is also an effective control measure.
Harvesting
The
appearance of traces of yellow colour on the fruit indicates that it is
ready for harvesting. The fruit is twisted until the stalk snaps off or
cut with a sharp knife. A long pole or a ladder is needed for tall
plants.
For papain production, latex is collected by tapping the
green unripe fruit. Four longitudinal incisions, skin-deep and 2—3 cm
apart, are made with a sharp, non-corrosive rod (glass, plastic or
horn). Latex is collected in a clean glass or porcelain container and
dried. Fruits may be tapped once a week, until they show signs of
ripening. The operation is best done early in the morning (before 10
a.m.). Dried latex is processed in the laboratory. Tapping results in
ugly scars on the fruit, although quality is unaffected. Tapped fruit
can be processed or used as animal feed.
Yield
In
the Philippines where papaya is mainly grown in home gardens or as
intercrop, the national average yield is only 15 t/ha per year. Yield
in ringspot-infested areas is far below this figure, but in
well-managed commercial papaya farms in the southern Philippines where
the disease is not yet present, the yield is over 30 t/ha. 'Subang 6'
and 'Taiping 3' average 34 t/ha in Malaysia. Average yield of
'Cariflora' in Florida is 35 t/ha, and more than 40 t/ha is common in
Hawaii.
A yield of 200 kg/ha of dried papain is considered good for
the first year of tapping; during the second year roughly half as much
is collected.
Handling After Harvest
Fruit
is placed in wooden or plastic crates and bamboo baskets lined with
shredded newspaper or dried banana leaves and transported to the
market. In East Java fruit is stacked loose on a truck — each fruit
wrapped in a piece of newspaper — and sent to Surabaya and Jakarta;
this way of handling entails heavy losses. If intended for export,
fruits are graded, wrapped in non-glazed tissue paper and packed in
cartons lined with shredded newspaper. Japan and other importing
countries with very strict quarantine regulations require pre-shipment
treatment as a safeguard against fruit fly infestation.
Genetic Resources
Modest
collections of papaya are maintained by the Malaysian Research and
Development Institute (MARDI) and the Institute of Plant Breeding,
College of Agriculture, University of the Philippines at Los Baños.
Research centres in Central and South America (Costa Rica, Mexico,
Brazil, Columbia, Peru, Venezuela, etc.), Hawaii, India and Australia
are very good sources of germplasm material.
Breeding
Good
fruit quality and resistance to diseases are the major objectives in
papaya breeding. In addition, short stature, precocity, long peduncles
to avoid fruit overcrowding and elimination of female-sterile
hermaphroditism and carpellody of the stamens are also being
considered. Resistance to ringspot virus has not been found in Carica papaya but is said to occur in other Carica species, including Carica cauliflora Jacq., Carica pubescens Lenné & K. Koch, and Carica pentagona Heilborn. Transfer of ringspot virus resistance from wild Carica
species to the papaya should have priority. Although tolerance has been
incorporated in some newer cultivars like 'Cariflora' and 'Tainung No.
5', the disease is still limiting the productive life of orchards and
is a very serious threat. Interspecific hybridization has not yet
yielded results. Researchers have been successful in rescuing hybrid
embryos from crosses involving Carica papaya x Carica cauliflora
and similar crosses, but there is still the problem of fertility of the
F1. Induced variation can supplement this effort. Production of
homozygotic diploids via anther culture will hasten the varietal
improvement work. Developing stable, true-breeding hermaphrodites will
reduce the traditional number of seedlings to be established per hill.
If the lethal factor involved kills the embryo due to early endosperm
degeneration, then embryo rescue is a promising approach.
Prospects
Papaya
is as productive and easy to grow as banana and pineapple. Indeed, in
home gardens and local markets it takes an intermediate position
between banana and pineapple, but in the larger markets and in world
trade papaya lags far behind. The main reasons must be the perishable
nature of the fruit and, in comparison with pineapple, the limited
appeal of the processed products.
The expanding world trade is based
on the small fruits of cultivars in the Solo group which lend
themselves much better to packing and shipping than the traditional
large fruits. The small-fruited cultivars have also gained a foothold
in South-East Asia, but the high cost of packing and transport
precludes a rapid increase in exports. Unless new developments favour
processing, papaya will continue to be mainly a fruit for home
gardeners and small fruit growers.
It is not clear what happened to
papain production after Tanzania was superseded by South America as the
leading producer in the 1960s; hence little can be said about the scope
for papain production in South-East Asia.
Literature
Abdon,
A.C., 1980. Food composition tables recommended for use in the
Philippines. 5th revised edition. Food and Nutrition Research
Institute, Manila. 313 pp.
Chan, Y.K., 1975. Papaya cultivation. Malaysian Agricultural Research and Development Institute, Serdang. 6 pp.
Chan,
H.T. & Tang, C.S., 1978. The chemistry and biochemistry of papaya.
In: Inglett, G.E. & Charolambous, G. (Editors): Tropical Foods,
Vol. 1. Academic Press, New York. pp. 33—55.
Conover, R.A., Litz,
R.E. & Malo, S.E., 1986. 'Cariflora', a papaya ringspot virus
tolerant papaya for South Florida and the Caribbean. HortScience 21:
1072.
Horovitz, S. & Jimenez, H., 1978. Cruzamientos
interspecificos e intergenéricos en Caricaceas y sus implicaciones
fitotécnicas. [Interspecific and intergeneric crosses in Caricaceae and
their agronomical implications]. Agronomía Tropical (Maracay) 17:
323—343.
Manshardt, R.M. & Wenslaff, T.F., 1989. Interspecific hybridization of papaya with other Carica species. Journal of the American Society for Horticultural Science 114: 689—694.
PCARRD, 1984. The Philippines recommends for papaya. Los Baños, Laguna. 58 pp.
Storey, W.B., 1969. Papaya (Carica papaya L.).
In: Ferwerda, F.P. & Wit, F. (Editors): Outlines of perennial crop
breeding in the tropics. H. Veenman en Zonen BV, Wageningen. pp.
389—407.
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