The food we eat depends completely on biological diversity — on the variations in hereditary information that are contained in seeds from distant regions, or in the seeds of wild, weedy relatives. Throughout history, the growing of food has relied on a steady flow of “new” and different germplasm to provide plants with the strength to resist diseases and, in some cases, to repel hungry insects; to adapt to changes in climate and terrain and too little or too much water; and to suit the desires of consumers.

Plant breeder Gideon Schaeffer specializes in searching for more nutritious varieties of rice. Schaeffer grew these plants from ancestors specially chosen for their high content of lysine, which, among its other benefits, helps with bone development in children. {Scott Bauer, USDA-ARS)

The genes of the plants we eat are constantly being exchanged and swapped around. In some cases the exchange takes place totally in Nature, as a result of environmental changes or through mutations in plants. Some of the exchange takes place artificially, with humans’ help, as well.

Since the beginning of this century, when science rediscovered the work on heredity of Gregor Mendel, plant breeders have crossed and re-crossed genetic “lines” (like families) of food crops, mixing the germplasm of, for example, one parent that has superior ability to withstand drought with another that is noted for high yield. If all goes well in such a crossing, the result will be a new variety, not found in nature, that yields well in arid regions.

Never-ending task.
Breeders never finish their work, because the need for new varieties never ends. Even a dream variety will sooner or later fall victim to insects or diseases that are adapted for it (for their germplasm is constantly being changed, too, to cope with the environment around them). So the breeder tries to keep a step ahead of the game. Having a great diversity of germplasm on hand is the key to staying ahead.

How do breeders do their work? The easy answer is “in different ways,” but in most cases it amounts to joining female and male parts of plants and letting them produce a new generation.

A plant breeder who wishes to cross (that is, combine the qualities of) two varieties of maize, in order to produce a third variety that he or she hopes will have the most desirable features of both parents, may use paper bags and glassine envelopes. The male portion of the maize plant is in the tassel at the top, and the female portion is found in the flower of cobs that grow at the base of some of the plant’s leaves.

Utah State University research assistant Mayme Seng uses the paper bag technique to pollinate Snake River wheatgrass. (Jack Dykinga, USDA-ARS)

To attempt to merge the desired qualities of males of Maize A with females of Maize B, the scientist (or more likely one of the scientist’s students) goes into the field and snips off or covers the tassels of Maize B. This insures that Maize B does not become fertilized by the male pollen on its own plant. To make doubly sure that “foreign” pollen doesn’t get to Maize B, the flower may be covered by a bag.

The researcher collects pollen from tassels on Maize A, then puts the pollen on the silk that grows out of the ends of Maize B’s cobs. Thus Maize B becomes pollinated by Maize A, and a hybrid maize is likely to result. In Nature, all this work is done by wind and pollinating creatures, such as bees.

Variations of the maize technique are used on many crops with which scientists want to experiment. These plants are said to use sexual reproduction. Another category of plant uses asexual, or vegetative, reproduction. In this case, portions of the plant’s body become detached from it (or are removed by humans), and they grow into individual plants themselves. The potato is one such plant; the banana is another. The resulting fruits are essentially clones of their parent plants.

Why spend all this time, effort, and money developing new varieties of foods? The links below will take you to two of the many reasons:

Resistance: The unending battle to outwit bugs and diseases.
The Green Revolution: A time when the world needed new varieties, and needed them in a hurry.

Next: Resistance — Agriculture home page — Glossary — Site map
Back to AboutBiodiversity home