Agriculture Reference
In-Depth Information
on wheat prices compared with other feed
grains. A very small portion of the world's wheat
and wheat fl our is used for industrial purposes
such as starch and gluten production (Morrison
1988).
Global efforts to increase wheat production
and to keep up with population growth and rising
demand have been relatively successful in main-
taining a steady increase in wheat yield, repre-
senting roughly a threefold increase over
production levels of the 1960s. It should be noted
that, despite dramatic increases in global wheat
production, in 2003 more than 800 million people
in the world suffered daily from severe under-
nourishment and hunger (http://www.fao.org).
Protein defi ciency is one of the most serious prob-
lems and threatens to become a real nutritional
disaster in the near future, primarily in Asia and
Africa, where about 80% of the human diet is
protein supplied by plants. The urgent need to
increase high-quality protein sources is exacer-
bated by major problems affecting cultivated
crops, including the cereals, with respect to the
reduction in genetic diversity (Plucknett et al.,
1983, 1987).
In the future, the nutritional composition of
the world wheat supply will become even more
critical as world demand for wheat continues to
grow and world wheat stocks continue to decrease.
World population, which currently stands at well
over 6 billion, was projected in 2001 to reach 8.3
billion by the year 2030 and 9.3 billion by 2050
(http://www.fao.org). Income growth and urban-
ization, which are shifting consumer preference
away from rice, coarse grains, and tubers to more
wheat-based food products and meat, are also
expected to continue to increase in many devel-
oped and developing countries. World demand
is projected to require approximately a 66%
increase in agricultural production by 2040. In
addition, our ability to bring more land into wheat
cultivation is rapidly diminishing due to popula-
tion growth, environmental pressures, and the
increasingly limited availability of arable land
(Young 1999). The need for future improvement
in wheat production will clearly coincide with a
loss of fl exibility and availability of traditional
resources.
The success of wheat improvement programs
to meet future demands will require complement-
ing the traditional breeding approaches with
innovative, nontraditional methodologies that
will enhance genetic variation in wheat. One of
many approaches to improving wheat production
will be the manipulation of secondary and tertiary
gene pools for new sources of biotic and abiotic
stress tolerance. A key to the successful manipula-
tion of the primary, secondary, and tertiary gene
pools is to fully understand the evolution of the
cultivated wheat species. Unfortunately, some
loss of genetic diversity involving most of the
world's crops, including wheat, has accelerated in
recent decades. The dynamic conservation of
wheat germplasm and wild wheat relatives offers
one of the best hopes for sustained wheat improve-
ment (Nevo 1998). However, it is clear that con-
servation of germplasm is not the only answer. To
achieve a more effi cient and comprehensive utili-
zation of the gene pools of wheat and wild wheat
relatives, it is critical that we learn how to predict,
screen, manipulate, maintain, and properly evalu-
ate genetic diversity and resources (Nevo 2001).
After all, plant breeding is basically an accelerated
manipulation of natural evolution. Once we
understand the evolutionary processes involved
in the formation and stabilization of wheat, we
can better design wheat improvement programs
that will enable a more effi cient restructuring of
gene complexes within and between wheat, wheat-
related species, and genera to capitalize on the
value-added traits that may be economically
important for wheat improvement.
WHEAT CULTIVATION
Until the late 19th century, all cultivated wheat
existed as highly heterogeneous landraces. Wheat
cultivars were morphologically uniform mixtures
of inbred lines and hybrid segregates, the prod-
ucts of low levels of random crossing within a
landrace. Any artifi cial selection was primarily for
increased yield, larger seed size, better fl our
quality, and adaptation to a wider range of cli-
matic and farming regimes (Feldman et al., 1995).
Many landraces still exist today, in fi elds in many
