Publication
from Agroforestree Database: a tree reference and selection guide
version 4.0
by C. Orwa, A. Mutua, R. Kindt, R. Jamnadass and S. Anthony
Persea americana Miller
Local Names: Amharic (avocado);
Burmese (kyese, htaw bat); Creole (zaboka); English (butter
fruit, avocado, avocado-pear, alligator pear); Filipino (avocado); French
(avocat, avocatier, zaboka, zabelbok); German
(Alligatorbirne, Avocadobirne); Indonesian (avokad, adpukat); Khmer
(avôkaa); Malay (apukado, avokado); Mandinka (avacado); Pidgin English
(bata); Spanish (pagua, aguacate); Swahili (mparachichi, mpea, mwembe
mafuta); Thai (awokado); Trade names (medang); Vietnamese (bo, lê dâù)
Family: Lauraceae
Botanic
Description
Persea americana is a
medium to large tree, 9-20 m in height. The avocado is classified as an
evergreen, although some varieties lose their leaves for a short time
before flowering. The tree canopy ranges from low, dense and
symmetrical to upright and asymmetrical.
Leaves are 7-41 cm in
length and variable in shape (elliptic, oval, lanceolate). They are
often pubescent and reddish when young, becoming smooth, leathery, and
dark green when mature.
Flowers are yellowish green, and 1-1.3
cm in diameter. The many-flowered inflorescences are borne in a
pseudo-terminal position. The central axis of the inflorescence
terminates in a shoot.
The fruit is a berry, consisting of a
single large seed, surrounded by a buttery pulp. It contains 3-30% oil
(Florida varieties range from 3-15%). The skin is variable in thickness
and texture. Fruit colour at maturity is green, black, purple or
reddish, depending on variety. Fruit shape ranges from spherical to
pyriform, and weigh up to 2.3 kg.
Biology
Varieties are
classified into A and B types according to the time of day when the
female and male flower parts become reproductively functional. New
evidence indicates avocado flowers may be both self- and
cross-pollinated. Self-pollination occurs during the second flower
opening when pollen is transferred to the stigma while
cross-pollination may occur when female and male flowers from A and B
type varieties open simultaneously. Self-pollination appears to be
primarily caused by wind, whereas cross-pollination may be effected by
large flying insects such as bees and wasps. Varieties vary in the
degree of self- or cross-pollination necessary for fruit set. Some
varieties, such as 'Waldin', 'Lula' and 'Taylor' fruit well in solid
plantings. Others, such as 'Pollock' and 'Booth 8' (both B types) do
not, and it is probably advantageous to plant them in rows alternating
with other varieties (A types) which bloom simultaneously to facilitate
adequate pollination.
Ecology
West Indian and some
hybrid varieties are best adapted to a lowland tropical climate and
relatively frost-free areas of the subtropics. Mexican varieties are
more cold tolerant and not well adapted to lowland tropical conditions.
Guatemalan x Mexican hybrids are generally more cold tolerant than West
Indian x Guatemalan hybrid varieties. Some of the more cold-tolerant
varieties in Florida include 'Brogdon', 'Gainesville', 'Mexicola', and
'Winter Mexican'. However, it may be difficult to find plants of these
varieties. Moderately cold-tolerant types include 'Tonnage',
'Choquette', 'Hall', 'Lula', 'Taylor', 'Monroe', and 'Brookslate'.
Varieties with little cold-tolerance include 'Simmonds', 'Pollock',
'Dupuis', 'Nadir', 'Hardee' and 'Waldin'.
Biophysical
Limits
Altitude: 0-2 500 m, Mean annual temperature: -4 to 40 deg. C, Mean annual rainfall: 300-2 500 mm
Soil
type: Requires a well-drained aerated soil because the roots are
intolerant of anaerobic conditions; waterlogging for more than 24 hours
can kill trees. A pH of 5-5.8 is optimal for growth and fruit yield.
Documented
Species Distribution
Native: Antigua and Barbuda,
Barbados, Cuba, Dominica, Dominican Republic, Grenada, Guatemala,
Honduras, Jamaica, Puerto Rico, St Lucia, St Vincent and the
Grenadines, Trinidad and Tobago, United States of America, Virgin
Islands (US)
Exotic:
Angola, Benin, Botswana, Brazil, Burkina Faso, Burundi, Cambodia,
Cameroon, Cape Verde, Central African Republic, Chad, Chile, Congo,
Cote d'Ivoire, Democratic Republic of Congo, Djibouti, Egypt,
Equatorial Guinea, Ethiopia, Gabon, Gambia, Ghana, Guinea,
Guinea-Bissau, Haiti, India, Indonesia, Israel, Kenya, Lesotho,
Liberia, Madagascar, Malawi, Malaysia, Mali, Mauritania, Mexico,
Mozambique, Namibia, Niger, Nigeria, Papua New Guinea, Rwanda, Sao Tome
et Principe, Seychelles, Sierra Leone, Somalia, South Africa, Sudan,
Swaziland, Tanzania, Thailand, Togo, Uganda, Vietnam, Zambia, Zanzibar,
Zimbabwe
The
map above shows countries where the species has been planted. It does
neither suggest that the species can be planted in every ecological
zone within that country, nor that the species can not be planted in
other countries than those depicted. Since some tree species are
invasive, you need to follow biosafety procedures that apply to your
planting site.
Products
Food: The tree is grown for its
nutritious fruit that has long been important in the diets of the
people of Central America. Consumption is most often as an uncooked
savoury dish mixed with herbs and/or spices, as an ingredient of
vegetable salads, or as a sweetened dessert. However, its texture and
colour can be used to enhance the presentation and consumption of many
foods. Cooking impairs flavour and appearance of avocados. The flesh
represents 65-75% of the total fruit weight. The contents vary widely
in different cultivars. The approximate content per 100 g of edible
portion are: water 65-86 g, protein 1-4 g (unusually high for fruit),
fat 5.8-23 g (largely mono-saturated and documented as an
anti-cholesterol agent), carbohydrates 3.4-5.7 g (of which sugars only
1 g), iron 0.8-1 g, vitamin A and vitamin B-complex 1.5-3.2 mg. The
energy value is 600-800 kJ/100 g. The high oil content of the mature
fruit gives the flesh a buttery texture which is neither acid nor
sweet. The easily digestible flesh is rich in iron and vitamins A and
B; providing a highly nutritious solid food, even for infants.
Fodder: Surplus fruit is an important food source for pigs and other livestock.
Apiculture: Bees, important for
pollination and honey production, visit the avocado tree. The honey
produced is dark with a heavy body.
Timber: Wood of Persea
has been used for house building (especially for house posts), light
construction, furniture, cabinet making, agricultural implements,
carving, sculptures, musical instruments, paddles, small articles like
pen and brush holders, and novelties. It also yields a good-quality
veneer and plywood. More popular for its fruits the wood of avocado is
seldom used. The wood is brittle and susceptible to termite attack.
Lipids: The pulp and the seeds
contain fatty acids, such as oleic, lanolic, palmitic, stearic,
linoleic, capric and miristic acid which constitutes 80% of the fruits
fatty content. The oil is used by the cosmetic industry in soaps and
skin moisturizer products.
Poison: The unripe fruit is poisonous and the ground-up seed mixed with cheese is used as a rat and mouse poison.
Medicine: Recently
anti-cancerous activity has been reported in extracts of leaves and
fresh shoots of avocado. Oil extracted from the seeds has astringent
properties, and an oral infusion of the leaves is used to treat
dysentery. The skin of the fruit has anti-helmintic properties. The
avocado is also said to have spasmolitic and abortive properties. The
seed is ground and made into an ointment used to treat various skin
afflictions, such as scabies, purulent wounds, lesions of the scalp and
dandruff. The flesh is also used in traditional medicine.
Essential oil: Watery extracts of the avocado leaves contain a yellowish-green essential oil.
Tree
Management
Planting
distances depend on soil type and fertility, current technology, and
economic factors. In commercial groves, trees are planted from 5-7 m in
rows and 7-9 m between rows. Pruning during the first 2 years
encourages lateral growth and multiple framework branching.
Commercially, after several years of production it is desirable to
occasionally reduce canopy width of the trees to 5-6 m, to reduce
spraying and harvesting costs and reduce storm damage. Severe topping
and hedging do not injure trees. Planned tree removal is an option that
should be seriously considered for commercial plantings. An avocado
tree grown for its fruit production should either be from budded or
grafted trees that will produce fruit within 2 or 3 years as compared
to the 8-10 or more years required of seedling avocados. The fruit does
not generally ripen until it falls or is picked from the tree. Strong
winds or a heavy crop easily breaks limbs.
Germplasm
Management
The
seeds are recalcitrant; lowest safe mc is 57% mc for slow-drying, 57.4%
mc for rapid drying; are only viable for 2-3 weeks after removal of the
fruits. Storage is however possible in using several methods such as, 8
months in dry peat at 5 deg. C provided they are not permitted to dry
out, or for several months by dusting seeds with copper fungicide and
storing in damp sawdust or peat in airtight bags at 4-5 deg. C. A
germination percentage of 53-75% was observed after 1 year in moist
storage and fungicide at 4.4 deg. C.
Pests and
Diseases
Many
insect pests attack avocados but they seldom limit fruit production
significantly. Currently, the most important insect pests are avocado
looper (Epimecis detexta), pyriform scale (Protopulvinaria pyriformis), dictyospermum scale (Chrysomphalus dictyospermi), avocado red mites (Oligonychus yothersi), borers (Ambrosia beetles, Xylosandrus spp.), avocado lace bugs (Acysta perseae), and red-banded thrips (Selenothrips rubrocinctus).
Successful
control of foliar and fruit diseases caused by fungi requires that all
susceptible parts of the plant be thoroughly coated with the fungicide
before infection occurs. Sprays must be re-applied as new tissues
become exposed by growth and as spray residues are reduced by
weathering.
Trees in areas with poorly drained soils and/or which
are subject to flooding are likely to be affected by avocado root rot.
This is the most serious disease in most avocado-producing areas of the
world. Although many trees are infected with the fungus, the disease
only appears to be serious if trees are subjected to flooded
conditions. Leaves of infected trees may be pale green, wilted, and
necrotic and terminal branches die back in advanced stages of the
disease. Feeder roots become darkened and decayed and severely affected
trees usually die.
Sun-blotch (caused by a viroid) where symptoms of
infection include sunken yellow or whitish streaking or spotting and
distortion of twigs, leaves, and fruit, is transmitted through buds,
seeds, and root-grafting of infected trees. There is no control for
this disease, and infected trees should be destroyed. Algal leaf spot
whose symptoms appear first on upper leaf surfaces as green,
yellowish-green, or rust coloured roughly circular spots. Diplodia
stem-end rot begins at the stem end of the fruit and develops as the
fruit softens. Usually only a problem with immature fruit after harvest
and can be prevented by harvesting only mature fruit.
Cercospora
spot infection appears on fruits and leaves as small, angular, dark
brown spots with a yellow halo, which coalesce to form irregular
patches. Fruit lesions are frequently the points of entry for other
decay organisms such as the anthracnose fungus.
Avocado scab (the
scab fungus) readily infects young, succulent tissues of leaves, twigs
and fruit. These tissues become resistant as they mature. Lesions
appear as small, dark spots visible on both sides of the leaves. Spots
on leaf veins, petioles and twigs are slightly raised, and oval to
elongated. Severe infections distort and stunt leaves.
Spots on
fruits are dark, oval and raised and eventually coalesce to form
cracked and corky areas, which impair the appearance but not the
internal quality of the fruit. Begin a spray program for scab
prevention when bloom buds begin to swell and continue until harvest.
Further
Reading
Anon. 1986. The useful plants of India. Publications & Information Directorate, CSIR, New Delhi, India.
Bekele-Tesemma
A, Birnie A, Tengnas B. 1993. Useful trees and shrubs for Ethiopia.
Regional Soil Conservation Unit (RSCU), Swedish International
Development Authority (SIDA).
Cobley L.S & Steele W.M. 1976. An Introduction to the Botany of Tropical Crops. Longman Group Limited.
Crane E (ed.). 1976. Honey: A comprehensive survey. Bee Research Association.
Crane
E, Walker P. 1984. Pollination directory for world crops. International
Bee Research Association, London, UK.FAO. 1986. Some medicinal plants
of Africa and Latin America.
FAO Forestry Paper. 67. Rome.
Hong TD, Linington S, Ellis RH. 1996. Seed storage behaviour: a compendium. Handbooks for Genebanks: No. 4. IPGRI.
ICRAF.
1992. A selection of useful trees and shrubs for Kenya: Notes on their
identification, propagation and management for use by farming and
pastoral communities. ICRAF.
Katende AB et al. 1995. Useful trees
and shrubs for Uganda. Identification, Propagation and Management for
Agricultural and Pastoral Communities. Regional Soil Conservation Unit
(RSCU), Swedish International Development Authority (SIDA).
Lanzara P. and Pizzetti M. 1978. Simon & Schuster's Guide to Trees.
New York: Simon and Schuster.
Lemmens
RHMJ, Soerianegara I, Wong WC (eds.). 1995. Plant Resources of
South-east Asia. No 5(2). Timber trees: minor commercial timbers.
Backhuys Publishers, Leiden.
Mbuya LP et al. 1994. Useful trees and
shrubs for Tanzania: Identification, Propagation and Management
for Agricultural and Pastoral Communities. Regional Soil Conservation
Unit (RSCU), Swedish International Development Authority (SIDA).
Nicholson B.E, Harrison S.G, Masefield G.B & Wallis M. 1969. The Oxford Book of Food Plants. Oxford University Press.
Noad T, Birnie A. 1989. Trees of Kenya. General Printers, Nairobi.
Peter G von Carlowitz.1991. Multipurpose Trees and Shrubs-Sources of Seeds and Innoculants. ICRAF. Nairobi, Kenya.
Purseglove
JW. 1972. Tropical crops: Monocotyledons 2. Longman Group Ltd, UK.Sam.
1967. Avocado growing in Ghana. World crops. 2(5): 273-274.
Sosef
MSM, Hong LT, Prawirohatmodjo S. (eds.). 1998. PROSEA 5(3) Timber
trees: lesser known species. Backhuys Publishers, Leiden.
Timyan J. 1996. Bwa Yo: important trees of Haiti. South-East Consortium for International Development. Washington D.C.
Verheij
EWM, Coronel RE (eds.). 1991. Plant Resources of South East Asia No 2.
Edible fruits and nuts. Backhuys Publishers, Leiden.
Williams R.O & OBE. 1949. The useful and ornamental plants in Zanzibar and Pemba. Zanzibar Protectorate
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