Agriculture Reference
In-Depth Information
8
Avocado
Elhadi M. Yahia
INTRODUCTION
Avocado is a dicotyledonous plant from the Ranales order
and the Lauraceae family. It was classified as
Persea
gratissima
by Gaertner, and
Persea americana
by Miller.
P. americana
developed subspecies due to geographical
isolation that finally originated different botanical types.
The avocado tree (
Persea americana
Mill.) belongs to the
family
Lauraceae
and is one of the few commercially
significant members of the genus
Persea
. The fruit is
called 'Ahuacatl' by the Aztecs and from there derived
the term 'avocado', 'aguacate' (in Spanish), 'avocat' (in
French) and 'abacate' (in Portuguese). The Aztecs
considered avocados an aphrodisiac and called it
huacatl
,
meaning testicles, referring to the fruit's shape and the
way they hang from the tree. The fruit is also called
'palta' in Chile, Ecuador and Peru, and also has been
referred to as alligator pear, vegetable butter, butter pear
and midshipman's butter.
The avocado originated in Central America and southern
Mexico. Based on archaeological evidence found in
Tehuacán, Puebla (Mexico), it is believed that it appeared
approximately 12 000 years ago. It has been determined
that the centre of origin of this fruit is the central part of
Mexico, passing through Guatemala to Central America. In
this region, the natural gene stock can be found, which can
be useful to the biotechnological improvement of the
species. As evidence for this theory, primitive avocado
trees have been found in the 'Oriental Sierra Madre' along
from the State of Nuevo León (Mexico) to Costa Rica.
From this region avocado dispersed to the south-eastern
part of the United States, the West Indies, to a large part of
South America (Colombia, Venezuela, Brazil, Ecuador,
Peru, Bolivia and Chile) (Rodríguez Suppo 1992).
The avocado is botanically classified into three races:
(1) West Indian (WI),
Persea americana
Mill. var.
ameri-
cana
(
P. gratissima
Gaertn.), tropical with large variably
shaped fruit and lower oil content; (2) Mexican (MX),
P. americana
Mill. var.
drymifolia
Blake (
P. drymifolia
Schlecht.& Cham.), semi-tropical with smaller elongated
thin-skinned fruit and higher oil content; and (3) Guatemalan
(G),
P. nubigena
var.
guatemalensis
L. Wms., subtropical
with mostly round thick-skinned fruit and intermediate oil
content (Bergh & Lahav 1996). The Mexican race, which
originated in the mountains of México and Central America,
is characterized by relatively small fruit, ranging from 75 to
300 g, with a thin, smooth skin. Fruit of the Guatemalan
race are native to the highlands of Central America and are
not as resistant to low temperatures as those of the Mexican
race, characterized by large fruit, averaging 500-600 g, and
thick brittle skin. The West Indian race is native to the low-
lands of Central America and northern South America,
characterized by intermediate fruit size, with smooth, leath-
ery and sometimes glossy skin. There are differences in
fruit maturity and oil content between the different races
(Biale & Yo 1971). Generally, West Indian avocado trees are
the most cold sensitive and are damaged by temperatures
below 1.2°C (Joubert & Bredell 1982). While racial ances-
try was identified as the most important factor influencing
susceptibility to cold, other factors such as tree size, age and
vigour, crop load, and cultural practices were also shown to
