Agriculture Reference
In-Depth Information
therefore, it spread quickly. Seed producers and crop
breeders were able to respond quickly and altered the
combination of susceptible factors by the 1972 season.
Similar problems have been encountered with rice in
Southeast Asia. In the 1970s, the International Rice
Research Institute began releasing rice varieties with resis-
tance to specific pests, promoted them for planting over
broad geographic ranges. A short time after each variety
was adopted and planted widely, newly evolved biotypes
of the pests, such as the brown leafhopper, overcame the
resistance and decimated the crops. Each new variety of
rice lasted only 2 or 3 years before its level of resistance
was overcome by the rapid evolution by the pest (Chang,
1984). The lesson is clear: as long as only a few varieties
dominate, pests will be able to take advantage of the low
genetic diversity of the crop and overcome its resistance.
When failure occurs, farmers are totally dependent on the
infrastructure that produces new resistant varieties (or
provides chemical pesticides) since they no longer have
access to the genetic variability that used to be present in
their own fields (Altieri and Merrick, 1987).
In many ways, the overall success of agriculture in
developed countries over the past 3 decades has masked
the problem of genetic vulnerability. Surplus yields in
some regions can compensate for failures elsewhere.
But the regional failures are still happening, and the
potential exists for failures on a larger scale (Qualset and
Shands, 2005).
to recover the investment necessary to pay for these new
inputs and equipment, farmers often must intensify the
production of more profitable crops. This usually requires
a concentration of production in fewer and fewer crops, a
dependence on centralized market structures, a differently
skilled labor force, and further intensification of inputs to
reduce risk and the chance of crop failure. Technical
advice is relied upon (and usually paid for) from sources
outside the farm environment. The entire farm is forced
to change.
These changes too often result in farmers losing the
important local, traditional knowledge they have about
crops, the farm, and the farming process and relying on
genetic information that was developed under highly uni-
form, highly modified conditions. Cumulatively, the end
result is the loss of the local genetic diversity and cultural
experience that characterized farms before modernization.
The link between the erosion of genetic diversity in
livestock breeds and the input-intensiveness of conven-
tional livestock production, especially in CAFOs, has
already been touched upon in Chapter 1. The whole ratio-
nale of large-scale livestock production — to produce
large quantities of animal-derived food products at the
lowest cost — depends both on the management efficiency
gained through genetic uniformity and the tightly con-
trolled, input-dependent environment in which the animals
are raised. This topic will be discussed in greater depth
in Chapter 19.
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There is an important link between conventional agricul-
ture's control of genetic resources and its dependence on
external inputs, mechanization, and off-the-farm techno-
logical expertise. The dramatic reduction of the genetic
diversity of our crops and livestock breeds has been
closely paralleled by the dramatic increases in pesticide
and fertilizer production, irrigation and water use, mecha-
nization, and agricultural use of fossil fuels.
This link is very clear in the widespread use of hybrid
crop seeds. A modern hybrid crop variety is virtually
helpless outside the confines of the farm — it usually
cannot even reproduce itself from its own seed. At the
greatest extreme, the crop cannot succeed in a farming
system without very specific kinds of intensive, technol-
ogy-based human modification and control of the farm
environment.
When a farmer abandons local crop varieties for
hybrids, it is more than the hybrid seed that has to be
purchased. Every hybrid has a “package” of inputs and
practices that go along with the seed: soil cultivation
equipment, irrigation systems, soil amendments and fer-
tilizers, pest control materials, and other on-farm inputs.
The package also includes changes in many other aspects
of the farm organization and management as well. In order
Agriculture depends on more than just the genetic diver-
sity of crop plants and domesticated animals. Also
important is the genetic diversity of an array of other
organisms: (1) organisms in the natural ecosystems sur-
rounding agroecosystems, especially the wild relatives
of crop plants; (2) crops and animal breeds of minor
economic importance; and (3) beneficial noncrop organ-
isms such as parasitoids, allelopathic weeds, trees, and
soil organisms.
Wild relatives of crops are an important source of new
or novel variation in the directed selection process. They
have been important sources of new or stronger genetic
material, especially in the event of epidemics of the type
mentioned above. However, wild relatives, such as the
wild cotton in Figure 14.9, are disappearing rapidly in
many parts of the world because of deforestation and other
forms of habitat modification.
A similar kind of organism with potential value is the
natural cross between an escaped agricultural variety and
its wild relative. Such crosses are endangered as well
because the habitats where crops and wild relatives can
exchange genetic material are becoming rarer, mainly due
to the spread of hybrid seed into even the most remote
agricultural parts of the world, the simplification of the
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