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Lettuce is an annual plant of the daisy family, Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for salads, although it is also seen in other kinds of food, such as soups, sandwiches and wraps; it can also be grilled. One variety, the celtuce, is grown for its stems, which are eaten either raw or cooked. In addition to its main use as a leafy green, it has also gathered religious and medicinal significance over centuries of human consumption. Europe and North America originally dominated the market for lettuce, but by the late 20th century the consumption of lettuce had spread throughout the world. As of 2017, world production of lettuce and chicory was 27 million tonnes, 56% of which came from China.
A BLT is a type of sandwich, named for the initials of its primary ingredients, bacon, lettuce, and tomato. It can be made with varying recipes according to personal preference. Simple variants include using different types of lettuce, toasting or not, or adding mayonnaise. More pronounced variants can include using turkey bacon or tofu in place of bacon, or removing the lettuce entirely.
There are a number of lines of defence against pests and diseases in the orchard, principal among these being the practice of good husbandry, creating healthy soil and ensuring high standards of garden hygiene. But no matter how diverse and healthy the garden eco-system may be, there will always be a degree of disease and pest presence. In many ways, some level of pathogen population in the garden can be not only acceptable but desirable as they are indicative of a generally healthful and diverse environment, and add to the overall robustness of the system as an immunity to such detrimental influences will build up, particularly in a balanced polycultural regime. Indeed, most of the plants we grow will tend to be selected because they are trouble free, and those that are more susceptible to attack will have fallen by the wayside over time. However, most farmers find it unacceptable that the food crops they grow are damaged by pests.
Pistia is a genus of aquatic plants in the arum family, Araceae. It is the sole genus in the tribe Pistieae which reflects its systematic isolation within the family. The single species it comprises, Pistia stratiotes, is often called water cabbage, water lettuce, Nile cabbage, or shellflower. Its native distribution is uncertain but is probably pantropical; it was first discovered from the Nile near Lake Victoria in Africa. It is now present, either naturally or through human introduction, in nearly all tropical and subtropical fresh waterways and is considered an invasive species as well as a mosquito breeding habitat. The genus name is derived from the Greek word πιστός (pistos), meaning "water," and refers to the aquatic nature of the plants. The specific epithet is also derived from a Greek word, στρατιώτης, meaning "soldier," which references the sword-shaped leaves of some plants in the Stratiotes genus.
Leaf vegetables, also called leafy greens, salad greens, pot herbs, vegetable greens, or simply greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. Although they come from a very wide variety of plants, most share a great deal with other leaf vegetables in nutrition and cooking methods.
Lettuce big-vein disease causes leaf distortion and ruffling in affected lettuce plants.
Romaine or cos lettuce is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers. Unlike most lettuces, it is tolerant of heat. In North America, romaine is sold as whole heads or as “hearts” that have had the outer leaves removed and are often packaged together.
Maror refers to the bitter herbs eaten at the Passover Seder in keeping with the biblical commandment "with bitter herbs they shall eat it.".
Lettuce mosaic virus (LMV) is a typical potyvirus, which causes one of the major virus diseases of lettuce crops worldwide.
Botryotinia fuckeliana is a plant pathogen, and the causal agent of gray mold disease.
Lactuca serriola, also called prickly lettuce, milk thistle, compass plant, and scarole, is an annual or biennial plant in the dandelion tribe within the daisy family. It has a slightly fetid odor and is commonly considered a weed of orchards, roadsides and field crops. It is the closest wild relative of cultivated lettuce.
Deep water culture (DWC) is a hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient-rich, oxygenated water. Also known as deep flow technique (DFT), floating raft technology (FRT), or raceway, this method uses a rectangular tank less than one foot deep filled with a nutrient-rich solution with plants floating in Styrofoam boards on top. This method of floating the boards on the nutrient solution creates a near friction-less conveyor belt of floating rafts. DWC, along with nutrient film technique (NFT), and aggregate culture, is considered to be one of the most common hydroponic systems used today. Typically, DWC is used to grow short-term, non-fruiting crops such as leafy greens and herbs. The large volume of water helps mitigate rapid changes in temperature, pH, electrical conductivity (EC), and nutrient solution composition.
Pseudomonas cichorii is a Gram-negative soil bacterium that is pathogenic to plants. It has a wide host range, and can have an important economical impact on lettuce, celery and chrysanthemum crops. P. cichorii was first isolated on endives, from which it derives its name. It produces 6-aminopenicillanic acid. Based on 16S rRNA analysis, P. cichorii has been placed in the P. syringae group.
Bremia lactucae is a plant pathogen. This microorganism causes a disease of lettuce denominated as downy mildew. Some other strains can be found on 36 genera of Asteraceae including Senecio and Sonchus. Experiments using sporangia from hosts do not infect lettuce and it is concluded that the fungus exists as a quantity of host-specific strains. Wild species, such as Lactuca serriola, or varieties of Lactuca can hold strains that infect lettuce, but these pathogens are not sufficiently common to seriously infect the plant.
Nacobbus aberrans is a plant pathogenic nematode.
Tylenchorhynchus is a genus of nematodes including many species of plant parasites. The classification of stunt nematodes - those including the genus Tylenchorhynchus - is unstable; many newly discovered species within this genus are reconsidered to be actually subspecies. Stunt nematodes such as Tylenchorhynchus and the closely related genera, Anguillulina and Merlinia, include more than 250 known species. Members of these genera possess similar anatomy and may be easily mistaken for one another. Some debate has led to the classification of single species under different names in two distinct genera.
Nutrient film technique (NFT) is a hydroponic technique where in a very shallow stream of water containing all the dissolved nutrients required for plant growth is re-circulated past the bare roots of plants in a watertight gully, also known as channels.
A lettuce sandwich is a wrap with lettuce substituted for the bread, or a sandwich with a filling consisting primarily of lettuce. It should not be confused with other sandwiches that use lettuce as one of many ingredients, such as the BLT sandwich or the tomato and lettuce sandwich. The lettuce sandwich has a long history in both the United States and the United Kingdom. It has been used as a metaphor to represent things like mundanity, weakness and poverty.
In 2006, there were several outbreaks of foodborne illness from spinach and lettuce contaminated by E. coli O157:H7.
Lettuce soup is a soup prepared with lettuce as a primary ingredient. It may be prepared with myriad lettuces and other ingredients, and some lettuce soups may use several cultivars of lettuce in their preparation. It is a part of French cuisine and Chinese cuisine. Cream of lettuce soup is a type of lettuce soup prepared using milk or cream. The soup may be served with toast or rolls as a side dish or with the soup atop them. It may be served as an appetizer, a side dish or as a main dish, and may be served hot or cold.