Genetic Diversity In Agriculture
Genetic variation is the raw material for the plant breeder, who must
often select from primitive and wild plants, including wild species, in search
of new genes. The appearance of new diseases, new pests, or new virulent forms
of disease causing organisms makes it imperative that the plant be preserved,
because it offers a potential for the presence of disease resistant genes not
present in cultivated varieties. Also, there are demands for new characters–
for example, high protein, improved nutritional factors, and fertility
restoration. As a result, plant breeders require a large and diverse gene pool
to meet ever changing needs.
A gene bank is a popular term that is used to describe repositories for
genes of living organisms. It is commonly used in the context of plant breeding
as I described above, but it also applies to the freezing and the storage of
animal sperm and embryos for use in animal husbandry or artificial insemination.
An understanding of crop origins and variations is necessary in
assembling genetic diversity in plant crops. In certain geographical areas
there has existed a rich source of variability in crop plants but the
encroachment of civilization has reduced the natural variability inherent in
primitive plant forms and related species of crop plants. Agricultural process,
as a result of new breeding programs, has reduced rather than increased crop
variability as improved cultivars, or varieties, are planted in wider and wider
areas and old cultivars, which may contain valuable genes, are lost. Crop
failures, which result in a smaller gene pool, have led to an increased
awareness of the need to preserve genetic diversity in plants. Efforts are
under way to increase collections of plant materials in various forms. Usually
these are preserved as seeds, but living plants, pollen, and cell cultures are
also used. In most gene banks, seeds are usually preserved under conditions of
low temperature and humidity. These collections must be periodically renewed by
growing the plants and producing new seeds. Increasing emphasis is also being
placed on preserving living collections of asexually propagated crops such as
species of fruits and nuts.
In the united states, germ plasm banks are handled in a state-federal
cooperative program. Internationally, a consortium of international, government,
and private organizations called the consultative group in in International
Agricultural research, (established in 1974), the International Board for Plant
Genetic Resources (IBPGR) to promote the activities of international plant
research centers that collect and preserve plant germ plasm.
Crop improvement is continuous. Professional plant breeders are
constantly working, through genetics, on the improvement of plants to meet
changing needs and standards. For example, with the introduction of mechanical
pickers for tomatoes, a tomato resistant to bruising by the machine was needed.
Such a variety was created by plant breeders.
Better, higher-yielding crop varieties have played an important part in
the increase in crop production per acre in the united states and some other
nations. Varieties of rice, cotton, vegetable-oil crops and sugar crops have
changed almost completely since the early nineteen fifties. By the late
nineteen sixties, most crop acreage in the united states was producing varieties
unknown to earlier decades. Best known of the improved crops are the many
varieties of hybrid corn that are planted on more than ninety-seven percent of
the total corn acreage in the united states. Government experimental
laboratories and commercial seed companies shared in the research and
development of the high-yield plant varieties that provide such superior
characteristics as resistance to cold, drought, diseases, and pests.
Improvements in livestock, such as more efficient use of feed, has added
greatly to the annual farm output. Such improvements are the result of breeding
and improved husbandry and veterinary techniques. Special purpose-stock has
been developed through selective breeding. It includes cattle that are able to
thrive in subtropical regions, hogs that yield lean bacon instead of lard, and
small and broad breasted turkeys.
Artificial insemination has become a major factor in cattle improvement.
In this technique the sperm of genetically superior bulls is used to inseminate
thousands of cows. In this way a herd can be upgraded significantly in a single
generation. However, some people feel that producing plants and animals that
conform to the needs mechanization and increased production has resulted in less
desirable farm products.