Amaranths. Amaranthus species
Fig. 4a. Red amaranths with red flowers
Fig. 4b. White amaranths.
Introduction
These plants have not yet received any attention from agricultural scientists in Southern Africa, as they have not been considered to show promise as a commercial crop. Amaranthus is one of the oldest food crops in the new world, with evidence of cultivation reaching back as far as 6700 BC (Agogino 1957; MacNeish, 1971). This is probably owing to the ability of these plants to adapt readily to new environments, an extremely broad climatic adaptability and their competitive ability, which permits cultivation with minimum management. This makes it an easy crop to cultivate and domesticate (Feine et al., 1979). The Genus Amaranthus contains about 800 species and is divided into two sections. The section Amaranthus includes those species, which are normally considered to be grain types, while the section Blitopsis includes the vegetable species. Amaranthus constitutes an important part of the diet in areas of South America, Africa and Asia (Grubben, 1976). Although it is also used as a grain, Amaranthus is more widely used as a pot-herb and in some instances supplies a substantial portion of protein, minerals and vitamins in the diet (Feine et al., 1979).
These indigenous leafy vegetables have the potential to provide a valuable source of nutrition in areas with hot, dry climates. They could fill a valuable niche in the production of food in rural areas where the climate is not conducive to the production of vegetables such as cabbages. They could be particularly valuable in areas with a low rainfall, as these crops will produce a viable yield under these conditions, whereas most of the exotic leafy vegetables require large amounts of water for successful production. In areas where people have to walk long distances to collect their water, most water is used for household purposes and there is very little available for use on a vegetable garden. Drought-tolerant vegetable crops would be invaluable in helping to alleviate malnutrition in these areas. However, before being able to fulfill this potential, more information on their cultivation requirements is needed. Also, careful attention should be paid to palatability if a plant is to be successfully grown as a commercial crop.
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Historical perspective and origins.
The cultivation of Amaranths dates from far back on earth, as evidenced by the discovery of Amaranths seeds in the caves of Tehuacan Puebla in Mexico from 5500 years ago. There is, however, some uncertainty as to the exact date of these discoveries.
It is believed that as long ago as 5000 years peoples began to master the cultivation of squash, peppers and amaranths. These cultivations represented about 6% of their food. The percentage after1500 years later rose to 14% due to the progressive domestication of maize, beans and gourds.
The cultivation of amaranths was at its height during the Aztec Empire. For the Aztec people the amaranths represented a value on the nutritional level, therapeutic and the ritual. Certain historical writings still mention in 1577 the amaranths as being one of the four major edible plants. Four centuries later, the amaranths had completely disappeared from the Mexican diet save for certain confectionery made from the seeds of it mixed with molasses and called â śAlegriaâ ť. These constitute the last vestige of the epic of the amaranths left in Central America, the dusk of some six thousand years.
The crop.
Amaranthus species are ancient cultivated crops that have long been neglected by western agriculturists and gardeners. The National Academy of Science lists amaranths (vegetable and grain) as one of 23 food plants that could be used to improve nutrition and the quality of life for people in developing countries (Marx, 1977). Leaves of vegetable amaranths are high in protein (17.4-38.3% of dry matter); the protein is 5% lysine and 4.4% sulfur-containing amino acids; both limiting in many vegetables and cereal grains (Lloyd 1986, Makus and Davis, 1984; Teutonico and Knorr, 1985). In addition, leaves of amaranths are nutritionally significant sources of carbohydrates, several vitamins and minerals, and dietary fiber (Betschart et al.; 1981, Mathai 1978; National Research Council, 1975; Okuno and Sakaguchi, 1981, Teutonico and Knorr, 1985, Tucker 1986). Organoleptic judging panels have described vegetable amaranths to be very acceptable (Abbott and Campbell, 1982).
Amaranthus, whether grain or leaf, constitute a veritable solar factory. The productivity of Amaranths varies considerably according to the variety, climate, richness of the soil, etc. It can yield between 500kg and 5 tonnes per hectare.
Leaves of vegetable amaranths are nutritionally significant sources of beta carotene (National Research Council, 1975). There have been concerns about the presence of oxalates in vegetable amaranths, which can bind calcium and so lower ionic calcium concentrations in the blood, leading to hypocalcaemia. Oxalates can comprise 0.2-11.4% of the dry matter in vegetable amaranths (Teutonico and Knorr, 1985), but levels of oxalates are significantly reduced by boiling leaves for ten minutes, which does not significantly reduce nutrient levels (Stafford et al., 1976).
Cultivation
Amaranths prefer well-drained fertile soils in open spaces. Plants tolerate a pH in the range 4.3 to 7.5. Plants should not be given inorganic fertilizers. Most, if not all, members of this genus photosynthesize by a more efficient method called the C4 carbon-fixation pathwayâ ™; this process is particularly efficient at high temperatures, in bright sunlight and under dry conditions.
Amaranths are easy to grow and reasonable yields can be produced even in poor soils (Afolabi et al., 1981; Dean 1986, Uzo and Okorie, 1983). The crop has few insect pest problems (Afolabi et al., 1981; Dean, 1986), but damping-off of seedlings by species of Pythium is a problem that plagues producers and breeders (National Research Council, 1984).
Uses
Rural subsistence farmers primarily use amaranths as leafy vegetables. The vegetable can also be used as feed for livestock. Leaves are eaten raw or cooked as spinach (Hedrick, 1972; Harris, 1973; Grieve, 1984). The leaves contain about 3.88% protein, 1.1% fat, 9.38% carbohydrate, 3.2% ash, 323mg Ca, 8.3mg Fe and are rich in vitamins A,C, and B1 (Reid, 1977). The leaves may also be used as a potherb in order to remove poison from the system (Duke and Ayensu, 1985). Seeds may be cooked or used as a cereal substitute in cakes or porridge (Harris, 1973). Seeds are very small; about 1.2mm in diameter, but they are easy to harvest and are very nutritious. They can be cooked whole, but become very gelatinous like this, and it is rather difficult to crush all of the small seeds in the mouth and thus some of the seed will pass right through the digestive system without being assimilated. An edible dye is obtained from the seed capsules.
Other than culinary functions, Amaranths also have medicinal functions. A fluid extract of the plant is used as an astringent internally in the treatment of ulcerated mouths and throats, and externally as a wash for ulcers and sores (Grieve.1984) The juice of the roots is used externally to relieve headaches (Manandhar, 2002) The plant has a reputation for being effective in the treatment of tumours and warts (Duke and Ayensu, 1985).
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