Onion (Allium cepa) is an economically important crop in the United States, generating over $900 million annually in farm receipts from 2000 to 2004 (88). U.S. onion production area ranges from 65,000 to 70,000 hectares annually, with over 80% of the summer production (54,000 hectares) in the western states. On average, 53 million metric tons of onion bulbs are harvested annually from nearly 3 million hectares worldwide. A significant portion of the U.S. and world supply of onion seed is produced in the western United States, primarily in the Pacific Northwest (124). The genus Allium includes various economically important cultivated species, including the bulb onion, chive (A. schoenoprasum), garlic (A. sativum), and leek (A. porrum) (10). At least 18 other Allium species are consumed as fresh vegetables, pickled, or used as flavoring. However, the bulb onion is the most economically valuable species. On average, worldwide production of garlic is valued at about 10% that of the bulb onion (10). Leek and bunching onion are the next most valuable species, with production concentrated in Europe and the Orient, respectively. Bunching onion (A. fistulosum) production also is important in some areas of the United States, such as California. The distinctive flavor or odor of Allium spp. is produced when plant tissues are bruised or cut, and the enzyme alliinase hydrolyzes S-alk(en)yl cysteine sulfoxide precursors to form volatile sulfur compounds (10). Onion, garlic, and their relatives, although primarily grown for food, are also used in traditional medicine, including the treatment of chicken pox, the common cold, influenza, measles, and rheumatism. Antimicrobial characteristics of alliums are likely the result of sulfur compounds. Research has demonstrated that extracts of onion and garlic decrease sugars, lipids, and platelet aggregation, and enhance fibrinolysis in blood, indicating that alliums may help prevent arteriosclerosis and other cardiovascular diseases (111).
