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Threats to Crop Plant Diversity
Prior to 1800, when the first seed companies were established, almost all vegetable seeds grown in the U.S. were imported from Europe. Gardeners saved seeds their crop had produced for use the following year. Families passed down their favorite seed varieties to their children, thus ensuring the crops' survival.
As commercial seed companies flourished, these "openly pollinated" heirloom seeds—pollinated by bees, birds, insects, and the wind—were gradually replaced by hybrids, genetically crossed plant varieties selected primarily for their ability to stand up to mechanical harvesting, cross-country shipping, and the uniform ripening time of their crops.
As these genetically uniform hybrids have replaced the myriad heirloom varieties, the genetic diversity of many crops has been severely reduced. And because just a few hybrids are so widely grown, they are more vulnerable to pests and disease; a single pest or disease pathogen could endanger an entire crop. Although plant breeders work hard to make the new hybrid cultivars resistant to pests and disease, the evolution of new, resistant strains of pests or diseases is an ongoing threat. The average life span of a new wheat variety, for example, is only five years before a newly evolved fungus attacks it.
Usually, the disease-resistant strain used by breeders to decrease crop vulnerability is found in a wild relative of the particular crop. Thus, wild relatives of crops are vital in ensuring world food supplies and must be protected in their native habitats.
Although an estimated 100,000 plant species have been eaten by humans, barely more than 150 species are now under cultivation; only 20 species are now producing the vast majority of the world's food.
According to the Lancaster, Pennsylvania–based Heirloom Seed Project (a source of heirloom seeds as well as information on vegetables and flowers grown by the Germans who settled in Pennsylvania in the 18th and 19th centuries), a 1984 U.S. Department of Agriculture inventory of seeds available from catalog sources showed that only 3 percent of the seeds listed in a similar USDA inventory conducted in 1903 were still available commercially. For example, of the 7,000 apple varieties available in the U.S. in 1900, over 5,000 were lost, and the remaining number was steadily declining.
Several organizations have been established to preserve heirloom varieties of open-pollinated plants. They include:
Seed Savers Exchangewww.seedsavers.org Native Seed/SEARCH
www.nativeseeds.org Seeds of Change
www.seedsofchange.org
The National Seed Storage Laboratory in Fort Collins, Colorado, is the primary seed bank in the United States with the responsibility for preserving seed of agricultural crops. Its primary focus is to store seeds that will help preserve the genetic diversity, and thus the survival, of crop plants. As part of the National Plant Germplasm System, a network of federal, state, and private organizations and individuals dedicated to the same goal, the laboratory also stores germplasm for other countries and permits free and unrestricted exchanges of its collections to researchers and breeders.
Seed banks are critical in the effort to preserve the genetic diversity of agricultural crops. However, crops must be grown in the field so that they can continue to coevolve with pests and diseases and develop resistance to them if they are to survive in the long run. For this reason, gardeners can play an important role in preservation of food-plant diversity by both growing open-pollinated heirloom varieties and growing a variety of crops.