Genetic Resources in Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 193

TABLE 14.2
Facets of Agrobiodiversity, with Trends for Each

Geographic Component

World Food System Region or Country Farm or Field

Food diversity:
number of food types
and species grown or
raised for food

Fewer species are satisfying
food needs globally. Example :
about 60% of the world's
dietary energy comes from
four plant species — wheat,
rice, corn, and potatoes

Regions and countries are
increasingly likely to
specialize in a few crops
or livestock types

It is increasingly common for
an individual farming
operation to raise one type
of livestock or one type of
crop (monoculture)

Species diversity:
number of breeds or
varieties of each food
species

Fewer varieties and breeds are being grown, and many of the
others are going extinct. Examples : three varieties of oranges
make up 90% of Florida's orange crop; four varieties of potatoes
produce over 70% of the world crop

It is increasingly common for
an individual farming
operation to grow or raise
one genetic line

Variety or breed
diversity: number of
unique genomes in
the plant variety, or
degree of uniformity
in the livestock breed

Pure line, synthetic, hybrid, and transgenic varieties — all highly
uniform — make up an increasing percentage of crops grown
worldwide

It is increasingly common for
an individual farming
operation to plant a single
genome. Example: a farm
that grows a strain of hybrid
corn

corn, and potatoes (FAO, 1999; Nierenberg
and Halweil, 2004).

landraces for genetically uniform, high-yield-
ing varieties (HYVs) (FAO, 1999; Nierenberg
and Halweil, 2004). • In 1993, 71% of the commercial corn crop in

the U.S. came from six varieties, 65% of the
rice from only four varieties, and 50% of the
wheat from nine varieties (Raeburn, 1995).

The loss of agrobiodiversity is a cause for concern
because it represents the loss of potentially valuable infor-
mation. If the accumulated genetic resources of thousands
of years of plant and livestock breeding and domestication
can be likened to a library full of topics, old and new, on
a vast array of subjects, then the impact of trends in con-
ventional agriculture can be c ompared to replacing that
library with one that loans only the current best-selling
paperbacks.
The genetic information we are losing has a variety
of proven and potential values:

• 70% of the U.S. dairy herd is Holstein, and

almost all chicken eggs sold (more than 90%)
are laid by one breed, the white leghorn
(Halweil, 2004).

• Since 1900, more than 6000 known varieties of

apples (86% of those ever recorded) have
become extinct (Fowler and Mooney, 1990), as
have half of the domesticated animal breeds in
Europe, and about 1000 breeds of poultry and
cattle worldwide (Hall and Ruane, 1993).

• In Iran, one of the cradles of agrobiodiversity,

only about one quarter of the total number of
varieties of wheat, rice, and sorghum account
for 70 to 85% of the total area planted in these
crops (Koocheki et al., 2006).

• Genetic diversity in general is the raw material

for plant and animal breeding. Loss of this
diversity may restrict opportunities for future
breeding efforts.

• Genetic diversity in a crop or livestock species,

as manifested by the existence of many local
landraces and breeds, allows the use of genetic
lines that are well adapted to the particular con-
ditions of specific localities. Locally adapted
genetic lines, both in crops and in livestock,
require fewer external inputs and are therefore
a basis for sustainable systems.

• Worldwide, the FAO estimates that 28 to 43%

of animal breeds are in danger of extinction,
and that somewhere in the world at least one
breed of traditional livestock dies out each week
(Thrupp, 2004; FAO, 1999).

• About four fifths of the maize varieties known

in Mexico in 1930 have been lost.

• During the 20th century, about 75% of plant

genetic diversity has been lost as farmers world-
wide have abandoned their local varieties and

• Genetic diversity in a crop variety or livestock

breed is an important component of environ-
mental resistance in the field. The broader the