From Plant
Resources of South-East Asia No 2: Edible fruits and nuts (PROSEA)
by A. P. George, and R. J. Nissen
Taxon
Annona squamosa L.
Protologue
Annona
squamosa: Sp. Pl.: 537 (1753).
Family
ANNONACEAE
Chromosome
Numbers
2n = 14 (16)
Vernacular
Names
— Annona squamosa:
Sugarapple, sweetsop (En). Attier, pomme cannelle (Fr). Indonesia:
sirkaja (Javanese), sarikaja (Sundanese, Sumatra), atis (Ternate,
Tidore). Malaysia: nona sri kaya, buah nona, sri kaya. Philippines:
atis. Cambodia: tiep baay, tiep srôk. Laos: khièb. Thailand: noina
(central), makkhiap (north-eastern), lanang (Pattani). Vietnam: na,
mang câù ta.
Origin and
Geographic Distribution
The
cherimoya is indigenous to the tropical highlands of Peru and Ecuador,
while the sugarapple is widely distributed throughout tropical South
America. Most hybrids resemble cherimoya in vigour and tree habit, but
exhibit flowering and fruiting characteristics intermediate to both
parents. Cherimoya is grown commercially in Chile, Bolivia, Spain,
United States and New Zealand; the sugarapple in Thailand, the
Philippines and Malaysia, and the atemoya in Australia, Florida, Hawaii
and Israel.
Uses
Fruits are normally eaten fresh. The pulp can be
utilized as a flavouring for ice cream. The green fruit and seed have
effective vermicidal and insecticidal properties.
Production
and International Trade
In
the 1980s annual production in important producing countries was for
cherimoya: Spain 15 000 t, Bolivia 6000 t, Chile 2300 t and Peru 400 t;
for atemoya: Australia 800 t, Israel 500 t and Florida 200 t; for
sugarapple: Thailand 75 000 t and the Philippines 6000 t. Chile exports
1000 t of cherimoya annually. Exports from other countries are
negligible.
Properties
Between
50—80% of the fruit of sugarapple is edible. The vitamin C content is
appreciable (35—42 mg/100 g) and slightly higher than in grapefruit.
The nutrient value of thiamine, potassium and dietary fibre is also
significant.
Description
Annona
squamosa. Shrub or tree, 3—6 m tall. Leaves oblong to narrowly
elliptic, 7—17 cm x 3—5.5 cm, slightly pubescent or glabrescent
beneath. Flowers extra-axillary, borne on the young branchlets, usually
in clusters of 2—4, sometimes solitary, on slender peduncles; outer 3
petals oblong, up to 2.5 cm long, green, purple at the base; inner 3
petals reduced to minute scales or absent. Fruit a globose or conical
pseudocarp, 5—10 cm in diameter, formed of loosely cohering or almost
free carpels, the rounded ends projecting to render the surface
tuberculate; surface greenish-yellow with a powdery bloom; pulp white
tinged yellow. Seeds dark brown.
Growth and
Development
All
three crops are semi-deciduous, sugarapple shedding its leaves in the
dry season, cherimoya and atemoya in the subtropics in spring.
Flowering coincides with the resumption of extension growth. Usually a
second flush of shoot growth — and sometimes a third —occurs during the
growing season, bringing out further flowers, but these are unlikely to
set fruit. In fact flowering can be brought about at almost any time of
the year by pruning and defoliation to force a new flush. Thus the main
flush and flowering may be advanced by removing the leaves 1—2 months
before they would normally be shed. Flowering is best on spurs and
short shoots and fails completely on the very vigorous shoots common in
young cherimoya and atemoya trees.
Poor fruit set is the main
factor limiting yield; it affects both the number of fruit and fruit
shape and size. The stigmas are receptive for only a few hours, a day
before the anthers of that flower dehisce. At that time the flowers are
just beginning to open and are not very accessible to visiting insects.
Only small beetles of the Nitidulidae have been shown to be effective
pollinators; 2—3 visits are needed to pollinate an adequate number of
stigmas for full fruit development. Pollen germination is very poor.
Varying degrees of compatibility exist between cultivars and species.
Hand pollination greatly improves fruit set. It takes about 30 days for
an emerging flower bud to reach full bloom; fruit ripens 4—5 months
later, but at low temperature maturation is greatly delayed and in the
subtropics the harvest goes on from late autumn to early spring.
Other
Botanical Information
In
the Philippines three types of sugarapple are grown; in addition to the
common green-fruited seeded type there are some trees bearing purple
fruit and others green seedless fruit. In Thailand named cultivars are
traded, including the green 'Fai' and the yellow, easy-to-peel 'Nahng'.
In both countries sugarapple is the most important of the annonaceous
fruits.
In Australia the atemoya 'Pink's Mammoth' is being
superseded by the more productive 'African Pride'. Under warmer
semi-tropical conditions 'Geffner', an Israeli selection, may be
preferred. Recommended cherimoya cultivars are 'Bays' and 'White'
(California), 'Fino de Jete' (Spain, yielding 100—150 kg/tree per year)
and 'Reretai', 'Burton's Wonder' and 'Burton' (New Zealand).
Ecology
Sugarapple
thrives in the tropics up to about 1000 m elevation and has the
reputation, particularly in India, of being a hardy, drought-resistant
crop. This is only partly correct. Although the rest period and leaf
fall enable the tree to bridge a severe dry season, it requires
adequate moisture during the growing season, responding very well to
supplementary irrigation. The importance of moisture is borne out by
the fact that in India as well as South-East Asia fruit set is largely
limited to the onset of the rains, notwithstanding the prolonged
flowering season.
Cherimoya and atemoya are at home in the
highlands above 1000 m with a dry season and have found their way to
the subtropics. They have a slightly greater cold tolerance (—3°C for
mature trees) and lower optimum temperatures for fruit growth and
maturation. Excessively high temperatures may cause premature ripening
and fermentation of the fruit. For atemoya it has been shown that low
relative humidity (less than 70%) shortens the receptive period of the
stigmas and leads to flower abscission; similar problems may explain
the poor fruit set in sugarapple before the rainy season. Cultural
methods which raise humidity in the orchard include close tree spacing,
windbreaks and overhead misting. Windbreaks are also needed to prevent
damage to trees swaying in the wind, most cultivars being shallow
rooted. Such damage appears to be at least partially responsible for
the incidence of collar rot.
Although the crops grow on a wide
range of soil types from sands to clay loams, higher and more
consistent yields appear to be obtained from trees grown on sand or
sandy loam soils. Moreover, vegetative growth can also be controlled
more easily through irrigation and fertilizing. On the heavier and more
poorly drained soil types, waterlogging is a major cause of floral
abscission and reduced fruit set. On shallow soils, mounding improves
the soil depth and drainage, and mulching encourages the development of
surface feeding roots.
Propagation
and planting
Annonas
are usually grafted onto seedling rootstocks of cherimoya or
sugarapple. Sugarapple rootstocks tend to reduce tree size. The most
common methods used are whip, whip and tongue, and cleft grafting.
Success rates are usually high if grafting is carried out with the
start of sap flow after the rest period. In the Philippines patch
budding prior to leaf abscission, i.e. during the cool and dry season
(November—February) is recommended.
Scion performance on
seedling rootstocks varies greatly with respect to growth rate,
susceptibility to waterlogging, water stress and bacterial wilt.
Propagation of cultivars on their own roots or on clonal rootstocks
would eliminate this variability. However, to date, propagation by
means of cuttings, layering and tissue culture techniques has not been
very successful. Current spacings range from 8 m x 6 m to 6 m x 4 m for
cherimoya and atemoya to 5 m x 3 m and 4 m x 3 m for sugarapple.
Husbandry
Early
training of the trees is essential to carry heavy crops without limb
breakage. For vigorously growing trees (mainly cherimoya cultivars) the
open goblet is the most suitable tree shape. Where growth is weaker,
trees with a central leader are preferred. Formative pruning is carried
out during the rest period.
In Thailand sugarapple is rejuvenated
each year to maintain fruit quality. Laterals weakened by bearing are
removed and vigorous replacement shoots are headed back. The trees are
pruned when the leaves are about to fall, leading to an early
resumption of growth. The new growth is supported by irrigation until
the rainy season sets in. In this way the harvest period is brought
forward.
Strong apical dominance in some cherimoya and atemoya
cultivars gives rise to vigorously growing whips which fail to flower.
These vigorous shoots are tipped during the growing season to stimulate
the emergence of flowering laterals. Axillary bud break can be improved
by removing the uppermost leaves after tipping. If these treatments do
not have the desired effect, chemical defoliation, either during early
bud break or in the middle of the growing season, is a last resort. A
range of defoliants has been tested and a mixture of 250 g urea and 1 g
ethephon (Ethrel(R)) per litre, plus wetting agent, has been most
successful.
Annona trees require uniform soil moisture from
flowering to harvest. Irrigation should be scheduled according to
tensiometer readings. High humidity within the tree canopy may be
maintained by using low delivery rate undertree or overhead sprinklers.
The
fruits have a high demand for potassium. Mature, high-yielding trees
may require between 2—4 kg/year of potash. Potassium leaf levels can be
maintained above the suggested critical level of 1% only by
applications before flowering. Annona trees are sensitive to zinc and
boron deficiencies. Where boron is deficient, borax at 2 g/m2 should be
broadcast over the ground area under the canopy. Zinc deficiencies can
be corrected by zinc sulphate heptahydrate sprays (0.1%) applied at
monthly intervals. Boron and calcium sprays during flowering and early
fruit set may also be beneficial in reducing the incidence of internal
fruit browning.
It may be possible to improve fruit set by releasing
large numbers of pollinator beetles in the trees on days when
conditions are conducive to set. Hand pollination is also very
effective in increasing fruit set and yield. In California, it is the
prime means of obtaining consistently high yields. Techniques for hand
pollination of atemoya flowers involve transferring the collected
pollen to the stigmas with a brush, or using puffers or pollination
guns to blow pollen onto the stigmas. The Japanese persimmon
pollination gun has proved highly successful in California. With
high-yielding cultivars such as 'African Pride', some fruit thinning
may be necessary to regulate crop load and to maintain fruit size.
Diseases and
Pests
The major root rot disease is bacterial wilt (Pseudomonas solanacearum).
Symptoms are collar rot, dark internal discolouration of the root wood
tissue, tree decline and eventual death. Chemical control of the
disease is not possible. Sugarapple rootstocks are highly susceptible.
The major fruit diseases are black canker (Phomopsis spp.),
diplodia rot (Botryodiplodia
spp.) and purple blotch (Phytophthora
spp.). The incidence of these fruit diseases increases under moist or
wet conditions. They can all be controlled by a regular spray programme
using either mancozeb or copper oxychloride
Harvesting
Fruits
are mature when a cream colour develops between the interstices of the
carpels and when carpels become smoother and less rounded. Picking
rounds have to be made every few days over a harvest period of about 3
months. Fruits are normally clipped from the trees and packed into
shallow trays prior to sending to market.
Yield
Yield
varies considerably with cultivar and species. The sugarapple is
relatively prolific, consistently producing between 10—15 t/ha per
year. With the atemoya and cherimoya, yields are more variable and
range from 5—20 t/ha per year.
Handling
After Harvest
Annona
fruits are soft and highly susceptible to mechanical injury, skin and
pulp blemish and fungal rots. The fruits have a post-harvest life of
only 2—5 days with a maximum cool storage of 2 weeks at 15°C and high
humidity.
Genetic
Resources
Considerable variation exists between cultivars and seedlings of
cherimoya and atemoya; sugar apples are less variable.
Germplasm
collections are held in Spain and New Zealand (mainly of cherimoya) and
in Australia and Florida (cherimoya and atemoya).
Breeding
Little
effort has been exerted to select more desirable Annona types. Breeding
programmes conducted in the Philippines in the early 1900s were not
successful in producing new commercial atemoya cultivars. An intensive
selection and breeding programme in Annona
species is being undertaken at Maroochy Horticultural Research Station,
Nambour, Australia. Interspecific crossing between the sugarapple,
cherimoya, atemoya and Annona
reticulata L. and Annona
diversifolia
Saff. is possible. Selections with round, symmetrical fruit of low
susceptibility to blemish and with a long post-harvest storage life are
sought.
Prospects
The prominent
place of the sugarapple in Thailand and the Philippines can be further
strengthened if the shelf-life of the fruit can be extended, either
through breeding or better post-harvest technology. This could make the
fruit more popular in other parts of South-East Asia too, particularly
in eastern Indonesia with its marked dry season.
The scope for superior cherimoya and atemoya cultivars in highland
areas and northern Thailand still needs to be investigated.
Literature
Gazit, S., Galon, J. & Podoler, H., 1982. The role of Nitidulid
beetles in natural pollination of Annona in Israel.
Journal of American Society of Horticultural Science 107: 849—852.
George,
A.P. & Nissen, R.J., 1985. The custard apple. Part 1. Species,
varieties and rootstock selection. Australian Horticulture 83: 100—107.
George, A.P., Nissen, R.J. & Brown, B.I., 1987. The custard
apple. Queensland Agricultural Journal 113: 287—296.
George,
A.P. & Nissen, R.J., 1988. The effect of temperature, vapour
pressure deficit and soil moisture stress on growth, flowering and
fruit set of custard apple (Annona
cherimola x Annona
squamosa) 'African Pride'. Scientia Horticulturae 34:
183—191.
Thakur, D.R. & Singh, R.N., 1965. Studies on pollen morphology,
pollination and fruit set in some Annonas. Indian Journal of
Horticulture 22: 10—18.
Thakur, D.R. & Singh, R.N., 1967. Pomological description and
classification of some Annonas.
Indian Journal of Horticulture 24: 11—19.
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