Randall Apperson, age 13, of Freeport, Ill., for his question:
'WHEN WAS PLANT BREEDING FIRST PRACTICED?
Plant breeding is the practical application of genetic principles to the development of improved strains of agricultural and horticultural crops. Stone Age farmers were the first to improve crops through selection, choosing at each harvest the largest seeds from the best plants for sowing the following year.
In carefully selecting seeds over thousands of years, the ancient farmers converted favored wild grass and legume species into such crops as corn, wheat and soybeans.
In the 18th and 19th centuries farmers attempted to speed up crop improvement. Some advances were made, partly through selection and partly through trial and error.
Plant breeders use numerous methods to develop new varieties, but their primary techniques of development are selection, hybridization and the use of mutations.
In practicing selection, plant breeders choose plants with desirable traits for further propagation and discard plants that are inferior for that trait. By doing so, plant breeders can select and reselect for the trait through successive generations, shifting the population in the desired direction.
Hybridization involves crossing plants of different strains or types to join in the progeny the desirable traits of both parents.
Backcrossing is a common variation of hybridization. This technique is often used to transfer into a desirable variety a beneficial trait from an otherwise undesirable parent. When desirable characteristics are fully developed in a hybrid plant and the plant can be propagated asexually by budding, grafting or cloning, then no further selection is necessary.
Occasionally an individual plant shows an important change in one or more traits arising from a spontaneous mutation. Usually a change in a single gene is involved. Mutations have brought about double flowered forms, weeping stems and dwarfism in ornamentals.
Doubling the number of chromosomes is another plant breeding technique that has been useful in improving some flower and crop plants, sometimes producing forms with increased vigor and with larger leaves, flowers and fruits. The chemical colchicine, an alkaloid extracted from the autumn crocus, is useful for this purpose.
Developments in plant tissue culture and genetic engineering are opening up new opportunities for plant breeders. In tissue culture, a single laboratory dish of plant cells can be the equivalent of a field with thousands of plants from which to select improved strains.
As genetic engineering techniques are perfected, breeders may be able to transfer a gene for pest resistance to a crop plant directly from a wild relative or even from an unrelated species, thus reducing the need for pesticides over vast fields of crops.
Such attempts were meeting with only quite limited success by the mid 1980s, however, and genetic modification through somoclonal variation techniques may prove more immediately useful.