Genetic Resources in Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 197

FIGURE 14.9 Wild perennial cotton (Gossypium sp.), Tabasco, Mexico. Wild relatives of crops can still be found in
situ in traditional farming systems.

farming environment that accompanies the use of
improved varieties, and the increasing separation between
agricultural and natural ecosystems.
Diverse agricultural habitats also contain many minor
crop species that are of considerable importance for the
entire system. Besides providing an array of harvestable
useful products, these crops contribute to the ecological
diversity of the system. They are part of the whole-system
energy flow and nutrient cycling process. Minor crops of
little or no current commercial value are preserved in
many traditional cropping systems, especially in the devel-
oping world. They could have promising value for future
use, but they too are disappearing as traditional systems
give way to modernization.
Apart from crops and crop relatives, agroecosystems
are also made up of a diversity of noncrop plants and
animals, including predators and parasites of pests, allelo-
pathic weeds, and beneficial soil organisms. Many of these
can play very important roles in maintaining overall
system diversity and stability (Chapter 16). Since their
presence and genetic diversity depends to a great extent
on the overall diversity of the system, they are threatened
by the tendency toward agroecosystem uniformity.

More generally, attention needs to be paid to the overall
genetic diversity of agroecosystems. A fully functioning
crop and farm system preserves all the genetic, ecological,
and cultural processes that produce diversity in the first
place. Biological control information, plant defenses,
symbionts, and competitors are all actively interacting and
preserving genetically based information that is of great
agroecological value. And since only a fraction of all this
information is in the germplasm of the key crop, loss of
farming habitats can be even more devastating than nar-
rowing of the crop gene pool itself.

PRESERVING AGROBIODIVERSITY

Sustainability requires a fundamental shift in how we man-
age and manipulate the genetic resources in agroecosys-
tems. The key theme in this shift is genetic diversity. Sus-
tainable agroecosystems are genetically diverse at every
level, from the genome of the individual organisms to the
system as a whole. And this diversity should be a product
of coevolution — genetic changes should have occurred in
an environment of interaction among the various popula-
tions. In this way, all of the component organisms — crop