REVIEW OF RELATED LITERATURE

Lettuce (Lactuca sativa L.) is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. In many countries, it is typically eaten cold, raw, in salads, sandwiches, hamburgers, tacos, and in many other dishes. In some places, including China, lettuce is typically eaten cooked and use of the stem is as important as use of the leaf. Both the English name and the Latin name of the genus are ultimately derived from lac, the Latin word for milk, referring to the plant’s milky juice. Mild in flavor, it has been described over the centuries as a cooling counterbalance to other ingredients in a salad (Wikipedia, 2009).

Origin

Lactuca sativa, the only domesticated Lactuca species, is a native to the eastern Mediterranean basin. Its early use probably was medicinal and for edible seed oil. A landrace lettuce, known as USDA Plant Introduction 251245, is used for seed oil (Rubatzky and Yamaguchi, 1997).
Wild types of lettuce often have prickly leaves and stems, are non-heading and bitter tasting, and contain abundance of latex. Domestication probably emphasized absence of spines, slow bolting, large non-shattering seed, less latex, and less tissue bitterness. Heading lettuce is a relatively recent cultivated crop, being first described as cabbage lettuce in 1543 (Rubatzky and Yamaguchi, 1997).