From Plant
Resources of South-East Asia (PROSEA)
by Koesriharti
Taxon
Annona muricata L
Protologue
Protologue: Sp. Pl.: 536 (1753).
Family
Annonaceae
Chromosome
Numbers
2n= 14 or 16
Vernacular
Names
Soursop
(En), Corossol épineux (Fr), Indonesia: sirsak, nangka belanda (Java),
nangka seberang, Malaysia: durian belanda, durian benggala, durian
makkah, Papua New Guinea: saua sap, Philippines: guayabano (Tagalog),
atti (Ibanag), llabanos (Bisaya), Cambodia: tiep banla, tiep barang,
Laos: khan thalot, khièp thét, Thailand: thurian-thet, thurian-khaek,
rian-nam, Vietnam: mang câù xiêm.
Origin and
Geographic Distribution
The
soursop is a native of tropical America where it is an important fruit
crop. It was one of the first fruit trees introduced to the old world
after Columbus discovered America - the Spaniards brought it to the
Philippines at an early date - and can be found growing in most
tropical countries.
Uses
Soursop can be consumed fresh
for dessert when fully ripe or mixed with ice-cream or milk to make a
delicious drink, as is done in Java, Cuba and parts of America.
However, more often the puree is consumed after squeezing the pulp
through a sieve. It can be made into a fruit jelly, juice (with the
addition of sugar), nectar or syrup. It is also used in the preparation
of ice-cream. In Indonesia sweetcake ("dodol sirsak") is made by
boiling soursop pulp in water and adding sugar until the mixture
hardens. In the Philippines young soursop fruits with seeds that are
still soft are used as a vegetable. Mature but firm fruit may be made
into candies of delicate flavour and aroma.
Production and international trade
There
are no data on area and production in South-East Asia, except for the
Philippines where the average annual production in the late 1970s was
8500 t from 640 000 trees, 490 000 of which were of bearing age. With
more than 100 000 trees each, central Luzon and western Visayas are the
leading regions. The perishable nature of the fruit is a serious
handicap for production in orchards, but the tree is common in home
gardens and the fruit is found in markets throughout South-East Asia.
International trade is virtually limited to processed products, in
particular canned or bottled juice from countries in Central and South
America.
Properties
The soursop
consists of about 67.5% edible pulp, 20% peel, 8.5% seeds and 4% core
by weight. Sugars constitute about 68% of the total solids. Soursop is
a good source of vitamins B (0.07 mg/100 g pulp) and C (20 mg/100 g
pulp) and a poor to fair source of calcium and phosphorus. The most
desirable characteristic of the soursop is its extremely pleasing
fragrance and flavour. The flesh is like that of the cherimoya; the
pure white colour is very stable, also during processing.
Description
Shrub or small tree, 3-10 m tall, conforming to Troll's architectural model, branched from near the base.
Leaves oblong-obovate, 8-16 cm × 3-7 cm, short acuminate at apex; petiole 3-7 mm long.
Flowers
regular, in short 1-2-flowered inflorescences, greenish-yellow; pedicel
up to 2.5 cm long; sepals 3, triangular, persistent, about 4 mm long;
petals 6, in 2 rows; 3 outer petals broadly ovate, 3-5 cm × 2-4 cm; 3
inner petals 2-4 cm × 1.5-3.5 cm, with short claws at base; stamens
numerous, in many rows on a raised torus, 4-5 mm long, filaments
densely pubescent; ovaries numerous, densely pubescent, afterwards
confluent.
Ripe fruit a pseudocarp, broadly ovoid or ellipsoid, up
to 10-20 cm × 15-35 cm, dark green and covered with soft spines 6 mm
long, with fleshy, juicy white pulp.
Seeds numerous, obovoid, 2 cm × 1 cm, blackish-brown, shiny.
Growth and development
The
soursop tree branches freely through the emergence of sylleptic shoots.
Extension growth can occur at any time of the year and proceeds fairly
steadily; there are no prominent flushes. The emergence of flower buds
follows extension growth. The position of the flowers - mainly terminal
on short shoots and anywhere along the axis of long shoots - suggests
that they are initiated terminally, the meristem being pushed to a
lateral position as extension growth of the shoot is resumed.
A
dry season imposes synchronous shoot growth and flowering, leading to a
harvest peak 3 months later, but the synchronization is gradually lost
in the course of the rainy season.
The flowers are protandrous,
the pollen is shed as the outer petals open towards the evening. The
inner petals open much later and only very slightly, admitting small
insects attracted by the fragrance of the flowers. Presumably these
insects effect cross-pollination, though rather inadequately, for few
flowers set fruit and many fruits are misshapen since numerous ovules
are not fertilized.
Other botanical information
In
Indonesia and the Philippines sweet-fruited and sour-fruited types are
distinguished. The sweet type (Indonesia: "sirsak ratu") has small and
few-seeded fruits with a sub-acid flavour; it is the predominant type
in a few localities only. A similar distinction between sweet and sour
types is made in America.
Ecology
Soursop is the least
hardy of the Annona species, requiring a warm and humid tropical
climate. It grows at elevations up to 1000 m and as far as 25°S in
sheltered sites. Growth and fruiting are set back severely by cold
spells, and light frosts kill the tree. A dry season enhances leaf fall
and synchronizes extension growth and flowering to some extent. Yields
may be higher under these conditions, provided that high humidity
prevails during the period of fruit set; there are indications that, as
for other Annona spp., both
very high and low humidities may be detrimental to fruit set. Where
humidity tends to be low, a sheltered site is recommended to limit
transpiration (also because the tree is shallow-rooted). Most soils are
suitable, but drainage should be good because the tree does not
tolerate waterlogging.
Propagation and planting
Trees
can be propagated clonally, in particular through various budding and
grafting techniques on seedling stocks, as is the practice in parts of
America (e.g. Columbia, Venezuela). However, soursop is commonly raised
from seed. Seedlings are acceptable because populations are fairly
uniform - seeds of the sweet type, for instance, are generally true to
type - and because the juvenile phase lasts only 2-4 years. Seeds may
be sown directly in the field or in a nursery bed. Within 20-30 days
85-90% should germinate, and seedlings can be planted out after 6-8
months. Halving the leaves and temporary shading are necessary for
transplanted seedlings which have not been raised in containers.
Spacing in orchards should be 3 m × 4 m to 4 m × 6 m.
Being a
small and early-bearing tree, the soursop may be planted as an
intercrop between larger fruit trees such as mango, avocado, and
santol. When the main crop requires the space, the soursop trees are
grubbed out.
Husbandry
The
area around the base of the tree should be kept free from weeds or
covered with mulch to avoid dehydration of the shallow roots during the
dry season. The soursop can tolerate dry soil conditions, but the trees
shed too many leaves if they experience prolonged drought, and in that
situation they would benefit from supplementary irrigation. Application
of manure and/or NPK fertilizer in small doses a few times each year
promotes growth and fruiting, but no quantitative data on fertilizer
requirements or recommended leaf nutrient levels are available.
Trees
usually assume a satisfactory form, but in some cases it is necessary
to limit the tree to a single trunk by cutting out competing twigs as
early as possible. Water sprouts, interlacing and crowded branches
should also be removed. Inadequate pollination appears to be the main
factor limiting yield and hand pollination is often recommended.
However, it is rarely practised and is feasible only where there is a
definite flowering period.
Diseases and pests
As long as tree vigour is maintained, serious damage by diseases and pests is largely limited to the fruit. Anthracnose (Colletotrichum gloeosporioides)
is the principal disease of soursop in a humid environment. Fruit
production may be severely limited by infection of flowers and fruit,
which rot or shrivel; moreover, the disease affects maturing fruit and
leaves and stems as well. It has been suggested in the West Indies that
selection for the ability to set fruit under humid conditions is
worthwhile. Where there is a dry season it is perhaps possible to
advance flowering and fruit set by irrigation, in order to escape the
period of highest humidity. Brown stem rot (Corticium
sp.) infects and causes the decay of branches and may kill the tree. A
thorough clean-up at the end of the dry season, including burning of
the infected material, should help to contain the disease during the
wet season.
Scale insects often infest the trees and mealy bugs
may occur in masses on the fruit. If ants are adequately controlled,
natural enemies should be able to cope with these pests. Fruit can be
bagged to avoid damage from fruit flies. Annonaepestis bengalella is a fruit borer; the moth occurs from India to Java and the Philippines. The large caterpillars of Meganotron rufescens and those of Papilio agamemnon are often found eating the leaves. The damage caused by these last 3 pests generally does not warrant chemical control.
Harvesting
The
soursop fruits should be harvested when fully grown and still firm.
They are considered mature when their spines are set far apart and the
shiny green colour turns dull-green or yellowish-green. If picked
prematurely, fruit quality remains poor. On the other hand, fruits left
to ripen on the tree are often attacked by bats if they do not first
fall to the ground. In a non-seasonal climate, fruit may ripen
throughout the year, but usually there are 1-3 harvest periods, with a
prominent peak in the course of the main season.
The fruits have
to be picked selectively. They are cut from the peduncles using a sharp
knife or pruning shears and placed in bamboo baskets lined with soft
material such as straw.
Yield
Yields
are generally low: one or two dozen fruit per tree per year, each fruit
weighing more than 1 kg on average. More precise figures for a
35-year-old plot in Hawaii show that yields can be much higher: the
mean fruit numbers per tree were 33, 34 and 70 in the 4th, 5th and 6th
year after planting; at the rather low density of 215 trees/ha these
yields were equivalent to 9.2, 7.6 and 18 t/ha.
Handling after harvest
Harvested
fruit shows a two-stage rise in respiration. The first rise is
presumably triggered by detachment from the tree, the second is the
climacteric rise. Mature, firm fruit ripen 3-5 days after harvest and
can be held only 2-3 days thereafter, even if cooled. Thus, harvested
fruit should be dispatched to distant markets without delay. Because of
their tender skin, fruit should be handled with great care.
Ideally,
fruit to be processed should be stored in single layers so that each
day the ripe fruit can easily be selected for processing. These fruits
are washed in chlorinated water to remove dirt and reduce the microbial
load. The washed fruit is peeled and cored by hand to retain the pulp
for further processing.
Genetic resources
It
is not known whether soursop seeds can be stored long enough for
inclusion in germplasm seedbanks. Trees of "sirsak ratu" form part of
the germplasm collection at Subang, West Java. Soursop populations in
South-East Asia are rather uniform. Even in the Americas there are few
reports of deviating types, but the preference for clonal material in
Columbia and Venezuela may be an indication that variability is greater
in the centre of diversity.
Breeding
There has been little selection and breeding work: so far crosses of soursop with other Annona species have not been successful.
Prospects
Largely confined
to home gardens because of erratic yield and short shelf life,
production of soursop is too scattered to supply a substantial
processing industry. Presumably this is why soursop growing in
South-East Asia has not expanded convincingly in recent times.
Much
higher yields are within reach, mainly through better pollination. The
perishable nature of the fruit is not a problem if processors buy the
fruit in quantity. A breakthrough towards production in orchards
therefore seems feasible, particularly because the small tree size
facilitates orchard management and the short period from planting until
first crop reduces the risk involved in commercial production.
The
efficiency of orchard production can be greatly enhanced if the trees
grow synchronously as occurs in areas with a dry season. Intensive
pollination, growth regulation, crop protection and harvesting can all
be properly organized if the different stages of the crop cycle are
segregated in time.
Literature
Hendro Sunarjono, 1987. Ilmu produksi tanaman buah-buahan [Fruit growing]. Sinar Baru. Bandung, Indonesia. pp. 191-195.
Lam,
P.F. & Zaipun, M.Z., 1986. Respiration rates, ethylene productions
and chemical compositions of different maturity of soursop (Annona muricata L.) at various temperatures. MARDI Research Bulletin (Malaysia) 14(3): 231-235.
Nakasone, H.Y., 1972. Production feasibility for soursop. Hawaii Farm Science 21(1): 10-11.
Rismunandar, 1983. Membudidayakan tanaman buah-buahan [Development of fruit crops]. Sinar Baru. Bandung, Indonesia. pp. 147-151.
van
der Pijl, L., 1953. On the flower biology of some plants from Java with
general remarks on fly-traps. Annales Bogoriensis 1: 77-99.
Wijaya,
1988. Plasma nutfah sirsak [Soursop germplasm]. Warta Penelitian dan
Pengembangan Pertanian (Departemen Pertanian Republik Indonesia) 10(6):
1-2.
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