 Avocado
(Persea americana) is a tree and the fruit
of that tree, classified in the flowering
plant family Lauraceae. It is native to
Central America and Mexico. The tree grows
to 20 m (65 ft), with alternately arranged,
evergreen leaves, 12-25 cm long. The flowers
are inconspicuous, greenish-yellow, 5-10 mm
wide. The pear-shaped fruit is botanically a
berry or drupe, from 7 to 20 cm long, and
weighs between 100 to 1000 g. It has a large
central seed, 3 to 5 cm in diameter.
Avocado Recipes
An average avocado tree produces about 120
avocados annually. Commercial orchards
produce an average of 7 tonnes per hectare
each year, with some orchards achieving 20
tonnes per hectare (FAO statistics).
Biennial bearing can be a problem, with
heavy crops in one year being followed by
poor yields the next. The fruit is sometimes
called an avocado pear or alligator pear,
due to its shape and rough green skin. The
avocado tree does not tolerate freezing
temperatures, and so can be grown only in
subtropical and tropical climates.
Co-evolution theory
Barlow & Martin (2002) identify the avocado
as a fruit adapted for ecological
relationship with large mammals, now extinct
(as for example the South American
herbivorous giant ground sloths or the
Gomphotheres). This fruit with its mildly
toxic pit, co-evolved with those extinct
mammals to be swallowed whole and excreted
in dung, ready to sprout. The ecological
partners have disappeared, and the avocado
plant has not had time to evolve an
alternative seed dispersal technique, aside
from human cultivation.
Cultivation
This subtropical species needs a climate
without frost and not too much wind. When a
frost event does happen, the fruit drops
from the tree, reducing the yield. The
cultivar 'Hass' can tolerate temperatures
down to −1 °C. The trees also need well
aerated soils, ideally more than 1 m deep.
Yield is reduced when the irrigation water
has a high electrical conductivity. These
soil and climate conditions are met only in
a few areas of the world, particularly in
southern Spain, Israel, South Africa, Peru,
northern Chile, Vietnam, Indonesia,
Australia, New Zealand, United States, The
Philippines, Mexico and Central America, the
center of origin and diversity of this
species. (In the U.S., avocados are produced
commercially only in California and Florida,
although the varieties used are different.) |
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Propagation
and rootstocks
 While
an avocado propagated by seed can bear
fruit, it will take 4-6 years to do so, and
the offspring is unlikely to resemble the
parent cultivar in fruit quality. Thus,
commercial orchards are planted using
grafted trees and rootstocks. Rootstocks are
propagated by seed (seedling rootstocks) and
also layering (clonal rootstocks). After
about 1 year of growing the young plants in
a greenhouse, they are ready to be grafted.
Terminal and lateral grafting is normally
used. The scion cultivar will then grow for
another 6-12 months before the tree is ready
to be sold. Clonal rootstocks have been
selected for specific soil and disease
conditions, such as poor soil aeration or
resistance to the soil borne disease caused
by Phytophthora root rot.
Breeding
The species is partially unable to
self-pollinate, because of dichogamy in its
flowering. The limitation, added to the long
juvenile period, make it difficult to breed
this species. Most cultivars are clonally
propagated (via grafting), having originated
from random seedling plants or minor
mutations derived from cultivars. Modern
breeding programs tend to use isolation
plots where the chances of cross-pollination
are reduced. That is the case of programs at
the University of California-Riverside, as
well as the Volcani Centre in Israel.
Harvest and post-harvest
The avocado fruit does not ripen on the
tree, but will fall off or be picked in a
hard, "green" state, then it will ripen
quickly on the ground, but depending on the
amount of oil that it has, the taste may be
very different. Generally, the fruit is
picked once it reaches a mature size, and
will then ripen in a few days (faster if
stored with other fruit such as bananas,
because of the influence of ethylene gas).
Premium supermarkets sell pre-softened
avocados, treated with a special gas to
stimulate ethylene synthesis in the fruit
(the same process used to de-green lemons).
The fruit can be left on the tree until
required, rather than picked and stored, but
for commercial reasons it must be picked as
soon as possible. Growers can keep the fruit
on the tree for about 4-6 months after fully
developed; if the fruit stays on the tree
for too long it will fall to the ground.
Introduction to Europe
The earliest known account of the avocado in
Europe is that of Martin Fernandez De
Encisco in 1519. The plant was first
introduced to Indonesia by 1750, Brazil in
1809, Palestine in 1908, and South Africa
and Australia in the late 19th century.
Cultivation in California
The avocado was introduced to the U.S. state
of California in the 19th century, and it
has become an extremely successful cash
crop. 95% of United States avocado
production is located in California, and 80%
occurs in San Diego County [citation
needed]. Approximately 59,000 acres
(approximately 24,000 hectares) of avocados
are grown in California. Fallbrook,
California claims the title of "Avocado
Capital of the World" and hosts an annual
Avocado Festival.
While dozens of cultivars are grown in
California, 'Hass' (commonly misspelled
'Haas') is most common, accounting for more
than 80% of the crop. In appearance, Hass
has a dark, rippled skin and rich, creamy
flesh. All Hass avocado trees are related to
a single "mother tree" that was purchased as
a seedling by a mail carrier named Rudolph
Hass. He purchased the tree as a seedling
from A.R. Rideout of Whittier, California,
in 1926. Hass planted the seedling in his
front yard in La Habra Heights, California,
and patented the tree in 1935. All Hass
avocados can be traced back to grafts made
from that tree. The "Mother Tree" died of
root rot in 2002. Other avocado cultivars
include 'Bacon', 'Fuerte' (pictured),
'Gwen', 'Pinkerton', 'Reed' and 'Zutano'.
The fruit of the cultivar 'Florida', grown
mostly outside of California, is larger and
rounder, with a smooth, medium-green skin,
and a less-fatty, firmer and fibrous flesh.
These are occasionally marketed as
low-calorie avocados.
The avocado is unusual in that the timing of
the male and female phases differs among
cultivars. There are two flowering types,
referred to as "A" and "B" flower types. "A"
cultivars open as female on the morning of
the first day. The flower closes in late
morning or early afternoon. The flower will
remain closed until the afternoon of the
second day when it opens as male. "B"
varieties open as female on the afternoon of
the first day, close in late afternoon and
re-open in the male phase the following
morning.
Certain cultivars, such as the 'Hass', have
a tendency to bear well only in alternate
years. After a season with a low yield, due
to factors such as cold (which the avocado
does not tolerate well), the trees tend to
produce abundantly the next season. This
heavy crop depletes stored carbohydrates,
resulting in a reduced yield the following
season, and thus the alternate bearing
pattern becomes established.
As a houseplant
Avocado can be grown as a houseplant from
seed. Although it will not normally bear
fruit indoors, people enjoy it for its
greenery. It can be germinated in normal
soil in a large pot, or in a glass of water
with a piece of charcoal for deodorizing,
with the top half (the pointed end) held up
by toothpicks.
The fruit of horticultural cultivars range
from more or less round to egg or
pear-shaped, typically the size of a
temperate-zone pear or larger, on the
outside bright green to green-brown (or
almost black) in color. Though the fruit
does have a markedly higher fat content than
most other fruits, most of the fat in
avocados is monounsaturated fat, which is
considered healthy in the human diet. A
whole medium avocado contains approximately
25% of the recommended daily amount of
saturated fat. Avocados also have 60% more
potassium than bananas. They are also rich
in B vitamins, as well as vitamin E and K.
A ripe avocado will yield to a gentle
pressure when held in the palm of the hand
and squeezed. The flesh is typically
greenish yellow to golden yellow when ripe.
The flesh oxidizes and turns brown quickly
after exposure to air. To prevent this, lime
or lemon juice can be added to avocados
after they are peeled; vitamin C in the
juice acts as an antioxidant. The avocado is
very popular in vegetarian cuisine, making
an excellent substitute for meats in
sandwiches and salads because of its high
fat content. The fruit is not sweet, but
fatty, strongly flavored, and of smooth,
almost creamy texture. It is used as the
base for the Mexican dip known as guacamole,
as well as a filling for several kinds of
sushi, including California rolls. Avocado
is popular in chicken dishes and as a spread
on toast, served with salt and pepper. In
Brazil and Vietnam, avocados are frequently
used for milk-shakes and occasionally added
to ice cream. In the Philippines and
Indonesia, a dessert drink is made with
sugar, milk, and pureed avocado. In Central
America, avocados are served mixed with
white rice. The fruit is also pressed for
avocado oil production. In Chile it is often
used in Hamburgers, Hot Dogs and celery
salads.
Toxicity
Feeding avocados to any animal should be
totally avoided. There is documented
evidence that animals such as cattle,
horses, goats, rabbits, birds, dogs, cats,
and even fish [3] [4] can be severely harmed
or even killed when they consume the leaves,
bark or fruit. Avocados contain a toxic
fatty acid derivative known as persin [5]
and many animal organizations recommend
total avoidance of all parts of the plant.
The symptoms include gastrointestinal
irriation, vomiting, diarrhea, respiratory
distress, congestion, fluid accumulation
around the tissues of the heart and even
death. Birds seem to be particularly
sensitive to this toxic compound.
Negative effects in humans seem to be
primarily in allergic individuals.
Names
The English name for the avocado is derived
from its Nahuatl name 'ahuacatl', meaning
testicle (due to its shape), with influence
from the conquering Spanish. In some
countries of South America, such as
(Argentina, Bolivia, Chile, Peru, and
Uruguay), the avocado is known by its
Quechua name, 'palta'. In other
Spanish-speaking countries it is called "aguacate".
The name avocado pear is sometimes used in
English, as is alligator pear. The Nahuatl
ahuacatl can be compounded with other words,
as in ahuacamolli, meaning "avocado soup or
sauce", from which the Mexican-Spanish word
guacamole derives. In the U.S., the
popularity of guacamole has soared in recent
years, and as a result, the word has been
fully adopted into U.S.-English, though the
pronunciation is sometimes varied by
dropping the final 'e' sound or abbreviating
the word to its first syllable "guac". The
plural of avocado is avocados or avocadoes.
In Chinese, the avocado is evocatively
called the "butter fruit". |
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