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.
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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