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Legume Crops

The legumes (family Fabaceae) are second only to the grasses in terms of their importance for human food.

In most civilizations a legumes and grains were used as a nutritional duo: barley & lentils; rice & soybean; maize & beans

Nutritionally cereal grains are a source of carbohydrate and legumes are a source of protein

The fruit is called a legume. A legume consists of a single carpel that splits along its t o opposite margins to release its seedsits two opposite margins to release its seeds.

Pulses are the dried seeds of legumes used for human food.

Legume Crops

Legumes are a major source of dietary protein. Proteins are polymers of amino acids, and nitrogen is a major component of amino acids.

Therefore legumes require greater amounts of nitrogen than cereals. Where does the nitrogen in legumes come from?

Nitrogen, as N2, is the most abundant element in the atmosphere. But plants are unable to incorporate N2 directly into amino acids. Plants require a form of nitrogen that is chemically reduced, or fixed, typically as ammonium (NH4) or nitrate (NO3) ions that are present in soil and taken up by the roots as dissolved a e ( O3) o s a a e p ese so a d a e up by e oo s as d sso edions in solution.

Certain bacteria are capable of chemically reducing or fixing atmospheric nitrogen, N2, to NH4. One such group of bacteria (Rhizobium, Rhizobacter) forms symbiotic associations with the roots of legume plants.

These bacteria live in specialized nodules in the roots of the legume plant and they directly provide a source of fixed nitrogen that the plant can used to synthesize amino acids and proteins.

Legume Crops

Because the symbiotic nitrogen-fixing bacteria provide a source of useable nitrogen to the legume plant, nitrogen availability does not limit the growth of the plant.

As a result, all the tissues of legumes are higher in protein content than the comparable tissues of non legume plants. Even so, the symbiotic bacteria usually produce more fixed nitrogen than is needed by the plant, so the excess fixed nitrogen contributes to soil fertility. Legumes can be grown in crop rotations with non legume crops to restore nitrogen that is depleted by grasses.

Root nodules on soybean roots

Changes in Legume Crops with Domestication

Like the grasses, specific changes have been associated with the domestication of legume species. Cereals were probably the earliest domesticated crop plants, but legumes followed very soon after. Lentils and peas were being collected as wild seeds at about the same time that barley and wheat were beginning to be cultivated in the Near East.

Like grasses, most cultivated legumes are annuals. Traits that have been selected for in domesticated crops have been directed to increasing yields and maximizing harvesting.

Reduced seed scattering (analagous to seed shattering in grains)Increased seed sizeSynchronous flowering and fruit developmentUniformity of seed germination

Wild seeds typically have a dormancy requirement, and only a small percentage of seeds may germinate if planted the year after they are produced.So loss of seed dormancy would have been a crucial trait for early domesticated types of legumes.

Changes in Legume Crops with Domestication

Yields of legumesgenerally are lower than for grains, and have been more difficult to increase through breeding.

Between 1930 and 1990 yields of grains increased by about 11 times, but yields of soybeans only increased by about 3 times. Protein-rich legumes are more energetically expensive for the plant to produce than the carbohydrate rich seeds of grasses.

Nutritional content of legumes per 100 grams

water % calories protein fat total carb

Pinto bean 8 350 23 1.2 64

Lentil 11 340 25 1.1 60

Soybean 10 400 34 18 33.5

Peanut 5.6 560 26 48 18.5

Peas 11.7 340 24 1.3 60

Pulses

Lentils

Lentils are one of the earliest cultivated plants. Carbonized lentils have been found in archeological sites in the Near East-Middle East dating to 8000 – 9000 years BP with larger seeds than the wild forms.

Lentil cultivation was closely associated with the domestication of barley and wheat, and hence was one of the “founder crops” of Old World agriculture. Lentils spread to southeast Europe with the cereal grain crops by 6000 – 7000 years BP, and to India around 4500 years BP.

Lens culinaris is the name for the cultivated lentil. L. orientalis is the wild form that is native to Turkey and Syria. The pods of the wild L. orientalis burst open at maturity but the cultivated L. culinaris has non-dehiscent pods. This trait is controlled by a single gene mutation and would have been observed and used by early farmers.

Lentil domestication involved loss of seed dormancy and development of nonshattering pods.

Lentils are about 25% protein, which is second only to soybean.

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Lentils are about 25% protein, making them a highly nutritious complement to cereals.

Lentils are able to grow in relatively dry areas. They are drought resistant and so are often grown as a rotational crop with wheat in the inland parts of the PNW.

A wide variety of lentils are still a major food staple in India, used in the traditional dals (dhals) which is a puree of different pulses, primarily lentils.

LentilsPulses Pulses

Peas

Peas, Pisum sativum, are the second of the pulses that constitute a part of the oldest complex of domesticated food plants. Carbonized fossil peas have been found in sites in present day Syria and Jordan dating to 8500 years BP. Wild, rough textured peas also had apparently been collected in the Near East and Mediterranean up to about 7500 BP.

Domesticated peas were present in Greece by around 7500 BP and the Rhine valley by around 6000 BP. Peas spread to India by 4000 – 3000 BP.

Wild i il t th d ti t d f ti t t T k hi hWild peas similar to the domesticated forms are native to western Turkey, which is the likely center of origin for peas.

Peas grow well in a variety of climates, from the warm Mediterranean to the cool climate of northwest Europe which allowed its adoption as a main protein crop by early European farmers.

As with lentils, the retention of the seeds inside the mature pod was a major domestication trait. Additional changes with domestication included increased seed size and reduction in the thickness of the seed coat.

Peas

Pulses

Dried peas were a mainstay of the peasant diet in Europe during the Middle AgesPease porridge was a thick broth made from dried peas.

Columbus brought peas to the West Indies in 1493, and peas came with European colonists to New England in the early1600s.

Most peas were consumed as dried pulses until the 1600s, when the first “garden peas” were developed and were quickly adopted as fresh greengarden peas were developed and were quickly adopted as fresh green vegetable.

Pulses

Chick peas

Chick peas, Cicer areitinum, are another ancient crop, first domesticated around 8500 BP in present day Iran.

But because chickpeas do not grow well in cooler climates, their spread with agriculture was mainly to the east, Afganistan and India, rather than west into Europe.

Today chickpeas and lentils form a major part of the diet in India parts of northern Africa Spaindiet in India, parts of northern Africa, Spain and Italy

Chickpeas were introduced to Mexico by the Spanish, and the Spanish name garbanzois used in North America.

Chick peas have easily digestible protein andare used to make a nonmilk based infant formula.

Pulses

Soybeans

Soybeans, Glycine max, is undoubtedly the most important contemporary legume crop worldwide in terms of value, production, and consumption.

Soybean is a relatively recently cultivated crop. It was domesticated in the Yangtze valley of China ca. 4000-3000 years BP and spread to Korea, Japan, and SE Asia by 3000 – 2000 years ago.

Changes in domestication of soybean included increased seed size and loss of the shattering pods. Very little soybean was grown in North America before the 20th

century but today the USA is the worlds largest producer at around 90 million metric tonnes.

PulsesSoybeans

Soybeans have the highest protein content (as much as 40%) and lowest carbohydrate of all the pulses. Soybeans are about 20% oil. In the US most of the soybean crop is used for oil and animal food. Only about 5% of the US crop is consumed directly as food.

Soybean is a highly versatile food however. It is used to produce a wide variety of food stuffs. It grows well in a warm temperate climate.

Because the fresh seeds of soybean are bitter and contain some undigestible sugars, raw soybeans undergo various treatments to increase their digestibility.

Miso, shoyu, tofu, tempeh, soy milk are produced using various microbial and fungal fermentations to partially digest the soy protein.

Dried soybeans are deficient in vitamin C, and one of the ways that this deficiency has been overcome in traditional diets is to sprout the beans. Soy sprouts contain high amoungs of vitamin C.

Soybean oil is processed into oil, plastics, paint and adhesives.

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Pulses

Pigeon pea

Pigeon pea, Cajanus cajan, are often used in the US as the main ingredient of split-pea soup, although ordinary peas are also used.

Pigeon pea probably originated in India and was domesticated about 2000 years ago. In India, pigeon pea is a major food staple, and India is the major producer of the world’s crop. Pigeon peas are used like lentils in the preparation of dals (dhals).

Unlike other pulses pigeon pea is a perennial shrub not annual plant It growsUnlike other pulses, pigeon pea is a perennial shrub, not annual plant. It grows well on poor soil and marginal agricultural land, making it an important food crop.

Pulses

Common Bean

Common beans, Phaeolus vulgaris, have a wide variety of cultivated forms. Pinto beans, kidney beans, navy beans, shell beans, pea beans, runner beans, green beans, wax beans and snap beans are all types of the common bean.

Common beans originated in the New World and were first domesticated independently in southern Mexico – Central America, and in the south central Andean region of South America (Ecuador-Peru).

Wild collected beans have been found dating to about 11,000 years BP to 8500 years BP in archeological sites in southern Mexico. But the earliest preserved domesticated forms date to about 2300 BP in Mexico, and around 4400 BP in Peru.

In southern Mexico, beans, maize and squash formed the basis of the milpas farming system of the Olmec, Zapotec, and Mayan civilizations of southern Mexico. By the time of European arrival in North America, common beans were cultivated throughout North, Central, and South America.

Pulses

Common bean

Common beans grow naturally as vines and so were historically grown with another plant such as maize to serve as a support. This mixed cropping system was also very advantageous because the nitrogen fixing bean plants provided ample nitrogen for the maize.

Native Americans, probably without realizing why, discovered that growing maize in combination with beans increased the yield of themaize.

Succotash is a Native Americandish that reflects the mixed crop systemmade from dried maize and dried beans.

Peanuts

Peanut, or ground nut, Arachis hypogaea, is another New World native from central South America Bolivia and Peru. Peanuts were widely cultivated in the warmer parts of South America when the first Europeans arrived ca 1500.

The oldest archeological records of peanuts are from Peru and date to 7600 years BP, but domestication was probably older.

Peanuts were introduced to Africa by the Portuguese, and have become a major dietary staple in west Africa Peanuts were also introduced to SE Asia

Pulses

major dietary staple in west Africa. Peanuts were also introduced to SE Asia and to the Philippines by the Spanish.

In the US peanuts are considered more of a nut or oil crop than as a pulse, but originally the seeds were cooked and eaten like other legumes, and are still used this way in Africa and China.

Pulses

Peanut

Peanut plants have a very unusual process of fruit development. The familiar peanut shells are the carpels, and enclose the peanut seeds, which are actually oil filled cotyledons.

But the peanut fruits develop underground.

After the flowers are pollinated the pedicelAfter the flowers are pollinated the pedicel begins to curve down. The cells below the ovary begin to divide and force the ovary into the ground.

After the ovary is pushed a few cm into the soil growth stops and the ovary develops into a fruit underground.

Peanuts are fruits, not roots or tubers.

Pulses

Although peanuts are native to the New World, they were actually brought to North America by way of Africa. Peanuts were a popular crop in Africa and were brought to the southeastern US by African slaves.

Peanuts are high in both fat and protein content, grow in poor soils, and thrive in the tropics, all of which contributed to their popularity as a subsistence crop in Africa.

In the US most peanuts are processed into peanut butter, which is a 20th century inventioninvention.

Peanuts, like maize, are highly susceptible to contamination by Aspergillus flavus, the fungus that produces the mycotoxin aflatoxin. Aflatoxin is the most carcinogenic natural product known. In fact aflatoxin was first discoved due to a mass poisoning of turkeys in England fed on peanut meal. The cause of “turkey X disease” was later shown to be due to aflatoxin. The USDA monitors aflatoxin levels in the US peanut crop, and the FDA limits the acceptable level of contamination to 20 ppb for human food.

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LegumesCarob

One last legume crop should be mentioned, but this is not a pulse.Carob comes from a tree, Ceratonia siliqua, which is native to the Mediterranean region. Carob trees are moderately large and grow well in warm temperate climates. Carob trees have been cultivated in the southwest US and Mexico.

The seed of carob are small and very uniform in size. They used to be used as a standard weight for small amounts of precious substances, like gold, and the word carat is derived from the seed of the carob.

Traditionally carob pods wereTraditionally carob pods were gathered from wild trees for the sweet mesocarp tissue that surrounds the seeds.

Modern uses are to produce carob flour from the pods which is used like cocoa. The seeds are processed for a gum that is used as a thickening agent in processed foods.