There are three ecological races, or types, of avocado:
Mexican—the leaves smell of anise. Small, slender, pear-shaped fruits (90–
it will survive down to minus 6°C. Not important commercially except when it is
hybridised with other types. Some botanists consider this type to be a separate
species, Persea drymifolia.
long stalks, with medium oil content of about 8–15%. Slightly less cold tolerant then
Mexican types, down to about minus 4.5°C. These are the so-called alligator types.
Sometimes classified as P.nubigena var. guatemalensis.
West Indian—large fruits (1–2 kg), on short stalks, with light coloured leaves.
The least hardy type, killed below about minus 2°C, it is adapted mainly to the hot,
low tropics. Sometimes classified as P.americana var. drymifolia.
Hybrids between these three types are widely grown—for example, the well-known
varieties Sharwil and Fuerte are Mexican X Guatemalan hybrids. There are
hundreds of varieties available, although many of them are only adapted to small,
specific growing conditions. Some varieties, such as Collinson, depend on other
varieties for pollination; other varieties are not actually dependent on others but they
do benefit from the additional pollen provided by another variety.
The plant is an evergreen tree, up to 20 m tall, with a shallow root system. The
growth of the tree is not regular, but occurs in “flushes” alternating with periods of
very slow or zero growth.
PLANTING
Propagation: although avocados do grow very easily from seed, commercial
grafted onto rootstocks of all types, but Mexican type rootstocks are incompatible
with West Indian type grafting material (scion).
Germination: before planting seeds the skin should be removed, in order to produce
better and faster results. Seed normally remains viable for 2–3 weeks after removal
from the fruit, or longer still if it is stored in a cool place, in dry peat.
Soil: avocados will grow in a wide range of soils but they are extremely sensitive to
waterlogging, and for this reason are often planted on mounds or other high spots.
They are classified as having only “intermediate tolerance” to salinity; optimum pH
is 6–7.
Fertiliser needs are similar to those for citrus, giving a good response to manure
and Nitrogen; a typical application would be 2 kg/tree/annum, at 3-month intervals,
of 12:6:10.
Spacing: 6–12 metres, depending on the variety. Some avocados are upright in their
growth habit, others have a more spreading type of growth.
Intercropping: sometimes with pigeon peas or other annuals, grown under younger
avocado trees. Cover crops or grass are often grown under the trees, to protect the
soil and also the trees’ shallow root systems.
240 g). The skin is light green and almost smooth. The most hardy of the three races,
Gu atemalan—medium-large (240–2200 g), compact, spherical fruits, on longGROWING FOOD – THE FOOD PRODUCTION HANDBOOK 245
earlier maturing plants. Guatemalan types and their hybrids can be successfully
growers use vegetative propagation in order to produce more uniform, predictable &