Lettuce（Lactuca sativaL.），It is an annual or biennial herb of Lactuca in Compositae.Its underground roots are vertical, its aboveground stems are upright, and its stems and branches are white;The leaves are oval with wavy edges and no hairs on both sides;The corolla is spherical, without hair outside, and the flowers are small and light in color;The fruit is light brown and oblanceolate;Seeds dark brown or gray white;Flowering and fruiting period: February to September。[9]according toTao Gu of the Song Dynasty in Qing Yi Lu[17]According to the records in, when an envoy from Kuang came to the Han Dynasty, people in the Sui Dynasty obtained vegetable seeds. It was named "lettuce" because its stem was as fat as bamboo shoots and came from Kuang”。[10]
Lettuce is native to Mediterranean coastal areas, mainly distributed inEuropeAmerica was introduced into China from West Asia in the fifth century. At present, it is cultivated in all parts of China。[11]Lettuce is a kind of cold resistant vegetable, which likes cold climate and does not tolerate high temperature;Moisture preference;It is suitable to grow in clay loam or loam with rich organic matter and water and fertilizer conservation.Its reproduction methods include asexual reproduction and sexual reproduction。[12]
Lettuce seeds can be used as medicine. They are bitter in taste and cold in nature. They have the effects of diuresis, lactation, heat clearing and detoxification. They are mainly used to treat poor urination, blood and milk blockage, insect and snake bites, swelling and poisoning, which are recorded in the "Three Rural Chronicles" and "Materia Medica"。[13]Lettuce contains a variety of vitamins and minerals, which can regulate the function of the nervous system and can be used as a home dish。[14]Lettuce is not only edible, but also has a certain literary value. Du Fu's "Cultivating Lettuce is always like a vegetable, but also like a child." Lettuce is a metaphor for a gentleman who "comes late"virtue.[15]
According to the records of Tao Gu in the Qing Yi Lu of the Song Dynasty, when the envoys from Kuang came to the Han Dynasty, the Sui people obtained vegetable seeds. The lettuce was named "lettuce" because its stem was as fat as bamboo shoots and came from Kuang”。[10]
morphological character
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Lettuce
Annual or biennial herb, 25-100 cm high.The root extends vertically.The stem is erect, solitary, and the upper panicle branches, all of which are white.Basal leafAnd the lower stem and leaf are large, undivided, oblanceolate, elliptic or elliptic oblanceolate, 6-15cm long and 1.5-6.5cm wide, with sharp, short acuminate or round tip, no stalk, heart-shaped or arrowhead shaped stem at the base, wavy or serrulate edges, and gradually smaller upward, the same shape or lanceolate as the primary leaf and the lower stem and leaf,The lower leaves of the panicle branches and the leaves on the panicle branches are very small, ovate heart-shaped, sessile, the base is heart-shaped or arrowhead shaped, the edge is entire, and all leaves are glabrous on both sides.
CapitulumMost or very many, arranged at the top of the stem and branchPanicle。InvolucreFruit stage ovoid, 1.1 cm long, 6 mm wide;The involucral bracts have five layers, the outermost layer is wide triangular, about 1 mm long and 2 mm wide, the outer layer is triangular or lanceolate, 5-7 mm long and 2 mm wide, the middle layer is lanceolate to ovate lanceolate, about 9 mm long and 2-3 mm wide, the inner layer is linear and long elliptic, about 1 cm long and 2 mm wide, all involucral bracts are acute at the top and hairless outside.About 15 ligulate florets.
Lettuce
acheneIt is oblanceolate, 4 mm long, 1.3 mm wide, compressed, light brown, with 6-7 fine veins on each side, the tip is sharp and forms a thin beak, the beak is thin and filiform, about 4 mm long, almost as long as the achene.Crown hairs are 2-layered, slender and slightly coarse.The flowering and fruiting period is from February to September.[1]
Varietal differentiation
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Chinese name and Latin scientific name
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one
Lettuce（Lactuca sativaL. var.angustataIrish ex Bremer）
Cultivated variety of lettuce with thick or extremely thick stems for eating and preparing pickles.[1]
Lettuce
two
Lettuce（Lactuca sativaL. var.ramosaHort.）
Cultivated variety of lettuce, with long obovate leaves densely forming cabbage shaped leaf balls for raw food.[1]
romaine lettuce
three
Iceberg lettuce（Lactuca sativaL. var.capitataDC.）
Cultivated variety of lettuce with round leaves curled into cabbage like leaves.[1]
Iceberg lettuce
Habitat
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Lettuce is native to Mediterranean coastal areas, mainly distributed in Europe and America. It was introduced into China from West Asia in about the fifth century. At present, it is cultivated in all parts of China。[11]There are also wild animals.[1][4]Lettuce is a kind of cold resistant vegetable, which likes cold climate and does not tolerate high temperature;Moisture preference;It is suitable to grow in clay loam or loam with rich organic matter and water and fertilizer conservation.It grows under the sparse forest on the hillside at an altitude of 20~150m.[12][16]
Growth habit
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Lettuce is a cold resistant vegetable.The germination temperature is above 4 ℃, and 15-20 ℃ is the best. If the temperature exceeds 30 ℃, the germination will not occur.Its seedlings can withstand low temperature below zero, the suitable temperature for seedling growth is 15-20 ℃, and the growth temperature for stem is 11-18 ℃.Lettuce likes large temperature difference between day and night. It requires higher temperature for flowering and fruiting, and the suitable temperature is 19-22 ℃.[2-3]
Lettuce
It is extremely sensitive to the state of soil surface water, and needs to supply water continuously to keep the soil moist.It needs a large amount of fertilizer, and should grow in clay loam or loam with rich organic matter and water and fertilizer conservation.Lettuce likes slightly acidic soil, and the suitable soil pH value is about 6.0.[3]
Reproductive methods
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There are two methods of lettuce reproduction: asexual reproduction and sexual reproduction。[12]
lettuce seed
When the seedling field is ready, the seeds shall be directly sown on the seedling field. After watering, the seedling field shall be watered with 4.5% Bestar emulsifiable concentrate 3000 times and 5% Kungfu emulsifiable concentrate 3000 times to prevent underground pests. The seedling field shall be 15-20 square meters per mu of field planting. Generally, the seed amount per mu of field shall be 25-30 grams, covered with sunshade net, and then compacted.
Generally, 4800-5200 seedlings are planted per mu at 32 × 35cm plant row spacing, and seedlings with swollen stems are eliminated during transplanting to avoid early bolting.[5]
cultivation techniques
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soil preparation
The root system of lettuce is weak, and the drought resistance is weak, so the soil with loose soil and water and fertilizer conservation should be selected.Till 15-21 cm before planting, apply 75000 kg of decomposed organic fertilizer per hectare, rake and level.Make a high border with a spacing of 120 cm and a width of 80-100 cm.The furrow shall be irrigated once 7 to 8 days before planting, and the film shall be covered 3 to 4 days later. The film shall be tightened and flattened to make it close to the ground, and the surrounding area shall be compacted with soil.[3]
Water management
The soil at the seedling stage should not be dry or too wet to prevent the seedlings from aging or overgrowth.Water should be properly controlled during rosette stage to promote the development of rosette leaves.The water supply shall be sufficient during the borrowing period. Low water will make the leaf bulb small and bitter. It is not advisable to have too much water at the late stage of heading to avoid cracking of the bulb and occurrence of soft rot.[3]
Fertilization management
The main root of lettuce seedlings is easy to pull out after the seedlings, which can produce a large number of lateral roots, and it is easy to survive after planting.The root setting water should be poured for 2-3 days to improve the vitality of planting.Before the stem lettuce is planted, sufficient base fertilizer shall be applied in combination with the soil ploughing and the whole border. 30000 kilograms of livestock compost and 450 kilograms of superphosphate shall be used per hectare;Or 1500 kg/ha of vegetable fertilizer;Or 750 kg urea per hectare, 450 kg superphosphate and 300 kg compound fertilizer.The base fertilizer accounts for 60% - 65% of the total amount, and 1050kg of quicklime is applied per hectare in strong acid soil.Keep the soil moist from seedling stage to lettuce expansion stage.In case of drought, water the "running water" every 3-5 days, and do not use too much fertilizer and water in the late growth period of seedlings to prevent overgrowth.When the plant height is 30-40 cm, it is necessary to control water appropriately to prevent excessive humidity between plants from causing diseases.At the beginning of lettuce expansion, fertilization should be from thick to thin.Too thick fertilization will easily lead to cracking at the base and rot.At this time, 1500g potassium dihydrogen phosphate per hectare or 0.2% - 0.3% borax can be sprayed once every ten days in combination with topdressing.In order to prevent early bolting or too high plants, paclobutrazol can be sprayed moderately. One month after planting, 90g paclobutrazol per hectare and 50kg water per hectare can be sprayed.Attention shall be paid to avoid repeated spraying or missing spraying, so as not to affect the yield and quality. The supply of fertilizer and water shall be stopped 10 days before harvest to promote stem maturity.One month after planting, soil shall be turned for 1-2 times.[3]
Lettuce
Disease and insect control
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downy mildew
The main diseases and pests of lettuce include downy mildew, sclerotinia, spot blight and aphids.The prevention and control of lettuce diseases and pests requires the comprehensive application of multiple prevention and control measures, and the combination of agricultural prevention and control, physical prevention and chemical prevention and control.The occurrence of downy mildew and spot blight can be effectively prevented by adopting appropriate sparse planting method, timely removing accumulated water and increasing light permeability.It is also an important physical control method to remove old and diseased leaves and burn them deeply.It can also be sprayed every 10 days with 200 times diluent of Bordeaux solution or 500 times solution of 65% mancozeb, which can also effectively prevent downy mildew and blight.Before sowing, use 10% salt water to remove the sclerotium in the seeds, which has a certain effect on preventing sclerotium disease.[2]
Key values
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medical
Lettuce seeds can be used as medicine. They are bitter in taste and cold in nature. They have the effects of diuresis, lactation, heat clearing and detoxification. They are mainly used to treat poor urination, blood and milk blockage, insect and snake bites, and swelling. They are recorded in the "Three Rural Chronicles" and "Materia Medica"。[13]
Lettuce can increase appetite, promote the secretion of digestive juice and gastrointestinal peristalsis, and is rich in potassium ions.It is extremely suitable for the elderly, pregnant women, long-term bedridden people and patients with hypertension, heart disease, dyspepsia and chronic constipation。[6]
Lettuce is sweet, cool, can pass milk, facilitate urination, digest food, sober up, repair bones and muscles, clean teeth, and remove breath.It can cure red and astringent urine, short urine, blood, etc.At the same time, the iron ion in lettuce is easy to be absorbed by the human body. Eating fresh lettuce often can prevent and cure iron deficiency anemia.[6]
edible
Lettuce contains a variety of vitamins and minerals, which can regulate the function of the nervous system and can be used as a home dish。[14]
Lettuce is a kind of common vegetable, which is delicious and tender. Its stems can be eaten raw, cold mixed, fried, dried or pickled.
Lettuce is low in calories. Among common foods, it is only slightly higher than winter melon, and its carbohydrate and fat content is also very low. It is a good food for people who want to lose weight and keep fit.[6]
Plant culture
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In Du Fu's "Cultivating Lettuce", "Lettuce is like a common vegetable, and it is like a child". Lettuce is used as a metaphor for a gentleman who "comes late"virtue.[15]
According to Qin Hua Zhou Leisure Record, there was a monk named Zhuo Yan in the Five Dynasties who lived by growing vegetables and selling money.One day at noon, he took a nap on the ground, and suddenly dreamed that a golden dragon flew out of the camp, eating lettuce.The monk wakes up suddenly, but the Mengyang scenery is still vivid, and he thinks that there must be a noble person coming.Looking up at the lettuce field, I saw a person with the appearance of Kuiwu Wei'an was about to take lettuce.He went forward humbly and took a large amount of lettuce as a gift to the stranger.When leaving, he told me: If you want to be rich and noble, don't forget each other.The man replied that if he is successful in the future, he must build a temple for the monk to thank him for his gift today.The "Pu'an Taoist Temple" is built here, symbolizing good luck.[7]
