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The lentil (Lens culinaris), also known as Lens esculenta, is an edible pulse. It is a bushy annual plant of the legume family, known for its lens-shaped seeds. It is about 40 cm tall, and the seeds grow in pods, usually with two seeds in each.

In South Asian cuisine, split lentils (often with their hulls removed) are known as lentils. Usually eaten with rice or rotis, the lentil is a dietary staple throughout regions of India, Sri Lanka, Pakistan, Bangladesh and Nepal. As a food crop, the majority of world production comes from Canada, India and Australia.

History
The history of lentil started by the origin of Agriculture. Lenti is the oldest pulse crop and probably one of the earliest crops domesticated in the Old World. It was found alongside human habitation up to 13’000 years BC and it was mainly grown in India, Bangladesh, Pakistan, Egypt, Greece, Italy, countries in the Mediterranean region and North America.

The origin of lentil is due to the near East and Central Asia.

Name
There are many different names in different parts of the world for the crop lentil. Here are just a few examples: lentil (English), adas (Arabic), mercimek (Turkey), messer (Ethiopia), masser or massur (India) and heramame (Japanese) are the most common names.

The first usage of the word lens to designate a specific genus was in the 16th century by the botanist Tournefort.

Systematics
The genus Lens is part of the subfamily Faboideae which is contained in the flowering plant family Fabaceae or commonly known as legume or bean family. This family is part of the order Fabales in the kingdom of Plantae.



Lens is a small genus which consists of the cultivated L. culinaris and six related wild taxa. Among the different taxa of wild lentils L. orientalis is considered to be the progenitor of the cultivated lentil and is now generally classified as L. culinaris subsp. orientalis. Therefore the genus Lens comprises seven taxa in six species:
 * Lens culinaris (and L. culinaris subsp. orientalis)
 * Lens odemensis
 * Lens ervoides
 * Lens nigricans
 * Lens lamottei
 * Lens tomentosus

Botanical description
Lentil is hypogeal, which means the cotyledons of the germinating seed stays in the ground and inside the seed coat. Therefore, it is less vulnerable to frost, wind erosion or insect attack.

The plant is a diploid annual bushy herb of erect, semi-erect or spreading and compact growth and normally varies from 30 to 50 cm (10 to 20 in) in height. It has many hairy branches and its stem is slender and angular. The rachis bears 10 to 15 leaflets in 5 to 8 pairs. The leaves are alternate, of oblong-linear and obtuse shape and from yellowish green to dark bluish green in colour. In general, the upper leaves are converted into tendrils, whereas the lower leaves are mucronate. If there are stipules, they are small. The flowers, one to four in number, are small, white, pink, purple, pale purple or pale blue in colour. They arise from the axils of the leaves, on a slender footstalk almost as long as the leaves. The pods are oblong, slightly inflated and about 1.5 cm long. Normally, each of them contains two seeds, about 0.5 cm in diameter, in the characteristic lens shape. The seeds can also be mottled and speckled. The several cultivated varieties of lentil differ in size, hairiness and colour of the leaves, flowers and seeds.

Lentil is self-pollinating. The flowering begins from the lowermost buds and gradually moves upward, so-called acropetal flowering. It takes about two weeks until all the flowers are open on the single branch. At the end of the second day and on the third day after the opening of the flowers, they close completely and the colour begins to fade. After three to four days the setting of the pods takes place.

Types



 * Brewer's: a large brown lentil which is often considered the "regular" lentil in the United States
 * Beluga, black, bead-like shape, lens shaped, dicotilidon, almost spherical, named for resemblance to Beluga caviar
 * Brown/Spanish pardina
 * French green
 * Puy lentils, Lens esculenta puyensis, (small dark speckled blue-green), Protected Designation of Origin name
 * Dark/Light Green
 * Indianhead
 * Yellow/tan lentils (red inside)
 * Red Chief (decorticated yellow lentils)
 * Eston Green (Small green)
 * Richlea (medium green)
 * Laird (large green)
 * Masoor (brown-skinned lentils which are orange inside)
 * Petite crimson/red (decorticated masoor lentils)
 * Macachiados (big Mexican yellow lentils)

Production


Lentils are relatively tolerant to drought, and are grown throughout the world. FAOSTAT reported that the world production of lentils for calendar year 2013 was 4,975,621 metric tons, primarily coming from Canada, India and Australia.

About a quarter of the worldwide production of lentils is from India, most of which is consumed in the domestic market. Canada is the largest export producer of lentils in the world, and Saskatchewan is the most important producing region in Canada (growing 99% of Canadian lentils). Statistics Canada estimates that Canadian lentil production for the 2009/10 year was a record 1.5 million metric tons. The most commonly grown type is the Laird lentil.

The Palouse region of eastern Washington and the Idaho panhandle, with its commercial center at Pullman, Washington, constitute the most important lentil-producing region in the United States. Montana and North Dakota are also significant lentil growers. The National Agricultural Statistics Service reported United States 2007 production at 154.5 thousand metric tons.

Soil requirements
Lentil can grow on various soil types, from sand to clay loam. It grows best in deep sandy loam soils with moderate fertility. A soil pH around 7 would be the best. Lentil does not tolerate flooding or water- logged conditions.

Lentils improve the physical properties of soils and increases the yield of succeeding cereal crops. Biological nitrogen fixation or other rotational effects could be the reason for higher yields after lentils.

Climate requirements
The conditions under which lentils are grown differ across different growing regions. In the temperate climates lentils are planted in the winter and spring under low temperatures and vegetative growth occurs in later spring and the summer. Rainfall during this time is not limited. In the sub-tropics lentils are planted under relatively high temperatures at the end of the rainy season and vegetative growth occurs on the residual soil moisture in the winter season. Rainfall during this time is limited. In West Asia and North Africa some lentils are planted as a winter crop before snowfall. Plant growth occurs during the time of snow melting. Under such cultivation seed yields are often much higher.

Seedbed requirements and sowing
The lentil requires a firm, smooth seedbed and most of the previous crop residues incorporated. For the seed placement and for lather harvesting it’s important that the surface is not uneven or has large clods, stones or protruding crop residue. It’s important that the soil is made friable and weed free so that seeding could be done at a uniform depth.

The plant densities for lentil are variable between genotypes, seed size, planting time and growing conditions and also from region to region. In south Asia a seed rate of 30–40 kg/ ha is recommended. In west Asia countries a higher seed rate is recommended and also leads to a higher yield. The seeds should be sown 3-4 cm deep. In agriculturally mechanized countries, lentil is planted using grain drill s, but elsewhere it is still hand broadcast.

Cultivation management, fertilization
A big problem in lentil cultivation are weeds. The short high of lentil and it’s slow growth makes the lentil poorly competitive with weeds. Weed competition can lead to very high yield reduction as compared to weed free plots. In addition to yield reduction, weeds often produce similar seeds like lentil, what leads to problems in separation. In inter cropping systems (what is a very common system for lentils) herbicides need to be carefully selected, so that they are safe for both crops.

Lentil is a legume, so it can fix atmospheric nitrogen in the soil in association with specific rhizobia. So the Lentil can fix two-third of its nitrogen needs from the atmosphere. Lentils grow under very low input conditions. Some nutrients are sometimes given through fertilizers, containing P, N, K and S .

Diseases
Below is a list of the most common lentil diseases.

Processing
A combination of gravity, screens and air flow is used to clean and sort lentils based on shape and density. After destoning, they may be sorted by a color sorter and then packaged.

A major part of the world’s red lentil production undergoes a secondary processing step. These lentils are dehulled, split and polished. In south Asia, this process is called dhal milling. The moisture content of the lentils prior dehulling is crucial to guarantee a good dehulling efficiency. The hull of lentils usually accounts for 6 to 7% of the total seed weight, which is lower than most legumes. Lentil flour can be produced by milling the seeds, like cereals.

Culinary use
Lentils are consumed in many ways. They can be eaten soaked, germinated, cooked, fried and baked. The most common preparation method is cooking. The seeds require a cooking time of 10 to 40 minutes, depending on the variety; shorter for small varieties with the husk removed, such as the common red lentil. Most varieties have a distinctive, earthy flavor. Lentils with husk remain whole with moderate cooking; lentils without husk tend to disintegrate into a thick purée, which leads to quite different dishes.[2] The composition of lentils leads to a high emulsifying capacity which can be even increased by dough fermentation in bread making.

Lentil dishes
Lentils are used worldwide to cook many different dishes. Lentil dishes are most widespread throughout South Asia, the Mediterranean regions and West Asia. In the Indian subcontinent, lentil curry is part of the everyday diet, eaten with both rice and roti. Boiled lentils and lentil stock are used to thicken most vegetarian curries. They are also used as stuffing in dal parathas and puri for breakfast or snacks. Lentils are also used in many regional varieties of sweets. Lentil flour is used to prepare several different bread varieties, for example Papadum.

They are frequently combined with rice, which has a similar cooking time. A lentil and rice dish is referred to in Arab countries as mujaddara or mejadra. In Iran, rice and lentil is served with fried raisin; this dish is called Adas Polo. Rice and lentils are also cooked together in khichdi, a popular dish in the Indian subcontinent (India and Pakistan); a similar dish, kushari, made in Egypt, is considered one of two national dishes.

Lentils are used to prepare an inexpensive and nutritious soup all over Europe and North and South America, sometimes combined with some form of chicken or pork. In western courties, cooked lentils are often used in salads.

Lentils are commonly eaten in Ethiopia in a stew-like dish called kik, or kik wot, one of the dishes people eat with Ethiopia's national food, injera flat bread. Yellow lentils are used to make a non-spicy stew, which is one of the first solid foods Ethiopian women feed their babies.

Lentils were a chief part of the diet of ancient Iranians, who consumed lentils daily in the form of a stew poured over rice.

Composition
According to the USDA National Nutrient Database, 100 g of raw lentils (variety unspecified) provide 353 calories; the same weight of cooked lentils provides 116 calories. Raw lentils are 8% water, 63% carbohydrates including 11% dietary fiber, 25% protein, and 1% fat (table). Lentils are a rich source (20% or more of the Daily Value, DV) of numerous essential nutrients, including folate (120% DV), thiamin (76% DV), pantothenic acid (43% DV), vitamin B6 (42% DV), phosphorus (40% DV), iron (50% DV), and zinc (35%), among others (table). When lentils are cooked by boiling, protein content declines to 9% of total composition, and B vitamins and minerals decrease due to the overall water content increasing (protein itself is not lost).

Lentils have the second-highest ratio of protein per calorie of any legume, after soybeans.

Digestive effects
The low levels of readily digestible starch (5%) and high levels of slowly digested starch make lentils of potential value to people with diabetes. The remaining 65% of the starch is a resistant starch classified as RS1. A minimum of 10% in starch from lentils escapes digestion and absorption in the small intestine (therefore called "resistant starch"). Additional resistant starch is synthesized from gelatinized starch, during cooling, after the lentils were cooked.

Lentils also have antinutrient factors, such as trypsin inhibitors and a relatively high phytate content. Trypsin is an enzyme involved in digestion, and phytates reduce the bioavailability of dietary minerals. The phytates can be reduced by prolonged soaking and fermentation or sprouting.

Breeding
Although lentil has been an important crop for centuries, lentil breeding and genetic research has a relatively short history compared to many other crops. Since the inception of The International Center for Agriculture Research in the Dry Areas (ICARDA) breeding programme in 1977 significant gains have been made. It supplies landraces and breeding lines for countries around the world, supplemented by other programmes in both developing (e.g. India) and developed (e.g. Australia and Canada) countries. In recent years, such collaborations among breeders and agronomists are becoming increasingly important.

The focus lies on high yielding and stable cultivars for diverse environments to match the demand of a growing population. In particular, progress in quantity and quality as well as in the resistance to disease and abiotic stresses are the major breeding aims. Several varieties have been developed applying conventional breeding methodologies. Serious genetic improvement for yield has been made, however, the full potential of production and productivity could not yet be tapped due to several biotic and abiotic stresses.

Wild Lens species are a significant source of genetic variation for improving the relatively narrow genetic base of this crop. The wild species possess many diverse traits including disease resistances and abiotic stress tolerances. The above mentioned L. nigricans and L. orientalis possess morphological similarities to the cultivated L. culinaris. But only L. culinaris and L. culinaris subsp. orientalis are crossable and produce fully fertile seed. Between the different related species hybradisation barriers exist. According to their inter-crossability Lens species can be divided into three gene pools: Crosses generally fail between members of different gene pools. However, plant growth regulators and/or embryo rescue allows the growth of viable hybrids between groups. Even if crosses are successful, many undesired genes may be introduced as well in addition to the desired ones. This can be resolved by using a backcrossing programme. Thus, mutagenesis is crucial to create new and desirable varieties. According to Yadav et al. other biotechnology techniques which may impact on lentil breeding are micro-propagation using meristamatic explants, callus culture and regeneration, protoplast culture and doubled haploid production.
 * 1) Primary gene pool: L. culinaris (and L. culinaris subsp. orientalis) and L. odemensis
 * 2) Secondary gene pool: L. ervoides and L. nigricans
 * 3) Tertiary gene pool: L. lamottei and L. tomentosus