After reading this article you will learn about:- 1. Origin of Amaranth 2. Commercial Production and Importance of Amaranth 3. Botany 4. Floral Biology 5. Cytology and Cytogenetics 6. Germplasm Resources 7. Breeding Objectives 8. Breeding Approaches 9. Biotechnology 10. Varieties 11. Future Prospect.
- Origin of Amaranth
- Commercial Production and Importance of Amaranth
- Botany of Amaranth
- Floral Biology of Amaranth
- Cytology and Cytogenetics of Amaranth
- Germplasm Resources of Amaranth
- Breeding Objectives of Amaranth
- Breeding Approaches of Amaranth
- Biotechnology of Amaranth
- Varieties of Amaranth
- Future Prospect of Amaranth
1. Origin of Amaranth:
The earliest dating of amaranth as a domesticated grain crop comes from archaeological digs at a cave in Tehaucan, Puebla, Mexico, where seeds of Amaranthus cruentus were dated as 6,000 years old, although Sauer (1993) notes that initial domestication could have occurred much earlier and in different locations.
The oldest known seeds of A. hypochondriacus appeared in the same caves about 1500 years BP, although domestication may have occurred earlier.
Sauer (1993) believes the progenitor of A. cruentus to be A. hybridus, which is currently found over a wide range of plains and mountains in North, Central, and South America. Amaranthus hypochondriacus has characteristics of both A. cruentus and the wild species A. powelli, and may be a hybrid of the two.
The origin of the third species of grain amaranth, A. caudatus, is more uncertain to Sauer. Amaranthus caudatus has been used in South America’s Andean highlands (Peru, Bolivia, Argentina) for centuries but the timing and location of domestication are unknown.
Amaranthus caudatus may have been domesticated from an early introduction of A. cruentus that then crossed with a wild Amaranthus in the region. Chan and Sun (1997) found evidence with isozyme and RAPD markers suggesting that A. hybridus is a common ancestor to all the cultivated grain species.
The archaeological record shows domesticated amaranth seeds appearing over a wide range, from Argentina into the southern United States. Grain amaranth was used by various Indian groups in the southwestern United States, and light-coloured A. hypochondriacus seeds dated to 1100 A.D. have been found in the Ozarks. Use of amaranth leaves, both from cultivated and wild amaranths, also seems to have been widespread.
India grows considerable amaranth. However, several events have triggered a resurgence of interest in amaranth, including evidence for its desirable protein characteristics. Over the last two decades, much has been learned about amaranth’s nutritional profile and production requirements.
Improved cultivars have been developed, although much plant breeding work needs to be done. Commercial production of amaranth is increasing in the United States, with production currently centered in the Great Plains, primarily western Nebraska.
Amaranth has been used in various processed foods such as breads, crackers, cereals, and cookies in the United Stated. Interest in grain amaranth use in other countries is also on the rise, based on reports from international participants at annual meetings of the Amaranth Institute.
The Rodale Research Centre (RRC), began an amaranth research project in 1976. In their 14 years of operations, the RRC breeders assembled a germplasm collection of approximately 1,400 accessions and developed many of the world’s most successful grain cultivars.
The RRC germplasm collection was donated to the North Central Regional Plant Introduction Station (NCRPIS) in 1990, where it is maintained as part of the USDA National Plant Germplasm Collection.
2. Commercial Production and Importance of Amaranth:
Grain amaranth’s commercial production in the United States began in the late 1970s, grew through the 1980s, and has fluctuated since then. The yearly U.S. planting in the 1990s has been very small, typically in the 800 to 1,200 ha range.
As with many small-area crops, over production has sometimes occurred when production increased too rapidly following a year with high prices and strong demand. The relatively high price of amaranth, usually 10-fold higher than the price of maize on a per-weight basis, has spurred farmers’ interest.
In the past 10 years, amaranth also has been grown for grain use in Iowa, Minnesota, North Dakota, Montana, Kansas, Pennsylvania, and in other scattered locations. Production of grain amaranth also is reported in a growing number of countries around the world, including China, India, Kenya, Mexico, Nepal, Peru, Russia, and several Eastern European countries. The largest area of the grain-type amaranth is in China, where 150,000 ha are reportedly grown for forage use.
The forage use of amaranth is established in both the tropic and temperate zones. In many tropical areas, where amaranth is consumed as a vegetable (potherb), amaranth Stover is fed to livestock after several harvests. Amaranth forage has succeeded as an animal feed in the temperate zone of China. In the United States, animals have always eaten wild amaranth, but not as a deliberately managed forage.
Vegetable types of amaranth are used across Africa, Asia, and the Americas. Amaranthus dubius, A. cruentus and A. tricolor are adapted for growth as leafy vegetables in areas with hot climates and especially in the hot, humid tropics where torrential rains during the monsoon season can create hazards for agriculture.
Ornamental amaranths of various species are found worldwide, having spread from Asia and the Americas in the Columbian exchange of plants. These ornamental amaranths are readily available as seeds to transplants in the United States and probably much of the world. Examples include brightly coloured A. tricolor bedding plants, and A. caudatus ‘Love Lies Bleeding’ plants with drooping rope-like inflorescences.
3. Botany of Amaranth:
The three grain-producing species (A. caudatus, A. cruentus, and A. hypochondriacus) have differences in agronomic performance. Amaranthus caudatus is grown at high elevations in South America and Asia ; and most accessions of it are prone to diseases and late maturity in the temperate zone.
Its flowers have short bracts so that the inflorescence is not bristly, its spreading styles are separated by a ‘U’-shaped cleft, and the sepals are obtuse. Amaranthus cruentus is the most photoperiod insensitive and widely-adapted grain species.
Its flowers also have short bracts, but its styles are vertical and parallel. Amaranthus hypochondriacus has been adapted to temperate photoperiods by plant breeders and is not disease prone. Its flowers have bracts that roughly equal the height of the styles, making the inflorescence bristly. Its styles join with a V-shaped cleft.
Two of the cultivated vegetable accessions from Bangladesh (PI 606281 and PI 606282) are presently identified as Amaranthus aff. blitum in the GRIN on-line database. The flowers closely resemble A. blitum, but the growth form is erect and single stemmed, and the leaves are red-purple as is found in A. tricolor.
Amaranihus caudatus includes a distinctive plant type with an orange determinate inflorescence. However, some authors regard it as a separate species, either A. edulis Speg. or A. mantegazzianus Pass. In the RRC type system it is Edulis. The USDA, ARS (1999) database lists A. caudatus subsp. mantegazzianus (Pass.) Hanelt, as a synonym of A. caudatus.
A number of studies have addressed phylogenetic relationship within Amaranthus and recent studies have utilized molecular techniques. Most amaranthus accessions are monomorphic, but there are considerable diversity among accessions.
Of 600 RAPD fragments generated from 27 primers, 39.9% were polymorphic within the cultivated grain species, 42.8% within the progenitor species, 51.0% within the vegetable species, and 69.5% within other wild species. Data on RAPD markers support the monophyletic origin of the cultivated grain species with A. hybridus as the common ancestor.
Transue (1994) used RAPD markers to classify 29 accessions of A. caudatus, A. cruentus, and A. hypochondriacus into three distinct groups, and classified 79 other accessions not previously assigned to species (all grouped to A. cruentus or A. hypochondriacus).
This study indicated these three species generally can be classified unambiguously despite overlap in variation for morphological traits, including the floral traits typically used for species identification. Analysis of 282 polymorphic RAPD markers indicated that A. hypochondriacus and A. caudatus are more similar to each other than either is to A. cruentus.
Zheleznov (1987) studied electrophoretic variation in seed proteins of wild cultivated Amaranthus, resulting in grouping of entries into seven biotypes based on banding patterns.
These biotype groups support the conclusions of previous studies regarding the close relationship of A. cruentus and A. hybridus, the similarity of A. caudatus and A. caudatus var. edulis, and the distinctiveness of A. caudatus and A. cruentus.
4. Floral Biology of Amaranth:
Most amaranth species are monoecious. The flowers can be terminal or axial, but are always organized into glomerulus within the inflorescence. Within the glomerules the first flower is generally staminate, and the later flowers are pistillate.
There are two kinds of exceptions to the usual monoecious pattern: the dioecious species and two species (A. spinosus and A. dubius) with separate staminate and pistillate glomerules within the inflorescence.
5. Cytology and Cytogenetics of Amaranth:
Most Amaranthus species are n = 16 or n = 17, but A. dubius is unusual for having n = 32. The grain amaranths are paleo-allotetraploids, as indicated by observations of pairing in their hybrids (Table 37.1).
These studies of pairing behaviour could be expanded to include more of the grain amaranth races and perhaps explain their erratic patterns of cross-compatibility. Outside of the grain amaranths, pairing behaviour has been studied for only a few of potential crosses.
Minor differences are expressed in the subscripts for the a and b genomes. The genomes are * = 8 except for B2 and C, which are x = 9.
6. Germplasm Resources of Amaranth:
Amaranthus germplasm has been collected for ex situ conservation. Most collections have less than 100 accessions, but six collections have substantial numbers of accessions (Table 37.2).
Amaranthus is well suited to ex situ conservation because the seeds are long lived and small. Brenner and Widrlechner (1998) described an efficient protocol for regenerating seeds of Amaranthus germplasm and maintaining genetic integrity ex situ.
Numerous major genes have been identified that may be useful for breeding. A few important ones are listed in Table 37.3.
7. Breeding Objectives of Amaranth:
1. Raising yield
2. Increasing harvest-ability
i. Lodging resistance
ii. Less seed shattering
iii. Timing of maturity
iv. Uniformity of maturity
v. Reduced leafiness in the green head area
vi. Reduced plant height
3. Good seedling vigour
4. Pest resistance/tolerance
i. Tarnished plant bug or sucking insect (Lygus lineolaris)
ii. Stem boring insect (Hypolixus)
iii. Damping off
5. Larger seeds
6. Good nutritional profile of seed (high seed protein, 14-16%)
7. Tolerance to cold
i. Heat tolerance
ii. Improved seedling establishment
iii. Resistance to diseases, insects and drought
8. Breeding Approaches of Amaranth:
Overcoming Seed Dormancy. The wild Amaranthus species and some vegetable accessions have seed dormancy. The cultivated and, especially, white-seeded grain types lack seed dormancy and will generally germinate in 3 to 4 days at 21°C or above.
A month or more of moist stratification at approximately 2 to 5°C, will overcome seed dormancy for many accessions. Germination can be achieved on blotter paper or sand. After stratification the seeds germinate well with 20°C (night) and 30 to 35°C (day).
Amaranth populations are easily managed because the plants can be miniaturized and their flowering cycle accelerated by controlling the environment. In a greenhouse, seeds should be planted approximately 0.5 to 1.0 cm deep in soil or transplanted with tweezers after germinating on moist blotter paper.
Cool temperatures (<20°C) can be harmful to amaranth plants. Twenty to 40°C is recommended. Seedlings of grain amaranths can be transplanted into the field 3 weeks after planting. Day-lengths shorter than 12 h will speed up flowering of most accessions, but not A. cruentus. Long-day lighting encourages vigorous vegetative growth.
The Amaranth Production Guide is a good reference for field management. Amaranths should be planted after the soil has warmed to 20°C or above. Amaranths can be vegetatively propagated from stem cuttings by using commercial rooting hormones. Finally, there is extensive literature on tissue culture, and in vitro culture as reviewed by Brenner et al. (2000).
Controlled crossing in greenhouses has been used successfully at the RRC. Crossing amaranths requires positioning or agitating synchronously flowering plants, so that when pollen is released, it will fall on the styles of the seed parent.
Genetic markers can be used to distinguish hybrids from the plants resulting from self-pollination. Inter-specific hybrids are usually distinctive enough that markers are not needed. The red/green trait is easily used, but other markers are also available. It is possible to emasculate, but if genetic markers are available, they are easier to use and more reliable.
Crossing is most easily accomplished in a greenhouse because plants in pots can be easily moved; photoperiods can be manipulated to synchronize flowering, and unwanted pollen can be excluded. However, adapted types that have synchronized flowering will cross naturally between adjacent field rows.
Many Amaranthus species are highly self-pollinated, limiting variability within accessions. Spontaneous genetic variation is low in these amaranths indicating the potential to obtain useful variability with induced mutation techniques. Mutants with a basal branching habit could be of economic value for vegetable production because the higher number of branches could increase leaf harvests, especially with improved regrowth ability.
The viable mutation frequency increased (2-8%) when the irradiation doses were increased (3-15 KR) for six Amaranthus genotypes tested, with the high doses yielding more early, and the lower doses more late- maturing mutants. Earliness could be advantageous for grain amaranths to escape drought and fit into crop rotations.
9. Biotechnology of Amaranth:
Although callus tissues can be readily obtained in amaranth, regeneration is recalcitrant. Bennici et al. (1997) determined that genotype, growth regulator dose and combination, and type and physiological stage of explants were critical factors in regeneration. Le et al., (1998) achieved rapid plant regeneration using thin cell layer explants of A. edulis. Culture systems also might be used in producing inter-generic hybrid calli.
Amaranths have a desirable spectrum of amino acid for human nutrition, especially a high lysine content often lacking in common ceieal grains. Accordingly, Raina and Datta (1992) cloned a gene for a high-quality 304 amino acid polypeptide from A. hypochondriacus.
A method for producing transgenic plants using their gene is patented and the gene functions in potato tubers. To identify and compare other protein genes for genetic transfer, Gorinstein et al. (1998) analyzed amino acid residues of A. caudatus with those of rice, garden pea, maize, and yam.
The glutelin fraction of amaranth, the most abundant polypeptide in the grain (Segura-Nieto et al., 1994), was electrophoresed with the aforementioned crops, and was found to have amino acid sequences similarities between 52 and 71%.
Restriction enzymes, cloning, and nucleotide sequencing have been applied to genomic DNA studies of A. paniculatus. A. particulars is a synonym of A. cruentus and to an amaranth gene encoding mitochondrial NAD-dependent malic enzyme.
Zeneca Limited (1996) has patented antimicrobial genes from Amaranthus to be incorporated into vectors. The resulting protein products are to be applied as antifungal or antibacterial agents.
10. Varieties of Amaranth:
Four amaranth cultivars have been registered in Crop Science: ‘Montana 3’ (‘MT 3’), ‘Montana 5’ (‘MT 5’), ‘Amount’, and ‘Plainsman’. Several lines have been developed by the RRC, NU-World Amaranth, and American Amaranth, and have been widely distributed and tested. All of the registered cultivars trace to materials developed by the RRC. ‘MT 3′ was a selection from RRC 1041’, MT 5 was a selection from ‘RRC 425’, and Amont was a selection from ‘MT 3’.
‘Plainsman’ was a selection from the cross ‘RRC 1024’ x ‘RRC 1004’ and widely distributed and tested as ‘K 343’ prior to release. ‘Plainsman’ has become the most widely grown amaranth cultivar in the U.S. due to its relatively high yield potential, lodging resistance, limited seed shattering, seed colour, maturity range.
Several others cultivars have been developed throughout the world, including Russia, ‘Pastevnyi 1’, ‘Turkestan’, and ‘Ural’, and South America, A. cruentus genotype “Anden’. Corke et al (1997) mentioned three Chinese lines in their discussion of amaranth research in China. The main cultivars in China are five RRC lines especially ‘RRC 1011’.
But, at least three new lines have recently been developed in China. ‘Noel Vietmeyer’, Oscar Blanco’, and ‘Alan Garcia’ were released from selection programs in Peru. Joshi (1985) developed ‘Annapurna’ from a selection program in India.
Annapurna’s average grain yield is 22.3 q/ha which is about 69% higher than that of another selection VL 21. The whitish creamy seeds of Annapurna contain about 14.5% protein. Its popping quality is excellent.
The distinguishing features of Annapurna are as follows:
1. Plant height: 220-225 cm.
2. Flowering: 75 days.
3. Maturity: 140-145 days
4. Stem: Stout, generally un-branched, ridged
5. Foliage: Leaf broad, dark green, lanceolate (24 X 12 cm ).
6. Inflorescence: Long (70 cm), green, compact terminal and lateral spikelet’s
7. Test weight: 0.8-0.9 g/1000 seeds.
8. Seed colour : Creamish white.
The nutritional value of vegetable amaranth has been extensively studied. The nutritional value has been rated equal or even superior to spinach, as it is considerably higher in calcium, iron, and phosphorous as well as fiber, niacin, and ascorbic acid on a fresh-weight basis and vitamin A, magnesium, and protein.
In parts of Africa, where the diet of rural people is high in carbohydrate and low in protein, leafy amaranth is a good source of protein, and is used heavily. Vegetable amaranths provide a high concentration of vitamin A, which is important for preventing eye diseases in the tropics.
Although vegetable amaranth contains oxalates and nitrates, they are not harmful for consumption under normal conditions of dietary intake. The levels of oxalates and nitrates are reduced by boiling the leaves. When grown under stressful conditions, vegetable amaranths produce higher levels of oxalate compounds, which could have adverse nutritional effects on humans or animals when utilized in quantities of more than 100 g of fresh greens daily.
The main use of leafy amaranth is as a cooked vegetable whose leaves and soft shoot parts are boiled in several changes of water for 10-15 minutes. When cooked, the leaves of A. tricolor are similar to spinach, with a fine, smooth-textured taste.
Sensory evaluation research done on amaranth entries from Asia and Africa showed that care must be taken in the choice of entries to be grown, as the eating qualities vary among species and selections, and that affects its acceptability as a vegetable crop.
Vegetable amaranths have a wide diversity in growth habit, leaf shape, colour, and size, plant size, and inflorescence characteristics, but typically they have broad leaves and low seed production.
The primary vegetable amaranths are A. blitum, A. cruentus, A. dubius, A. tricolor and A. hypochondriacus. Wild species are also commonly gathered as leafy vegetables. Amaranthus cruentus, A. dubius, and A. tricolor appear to be superior to other amaranth species for use as vegetables, as they have the highest leaf-stem ratio. Leaf-stem ratios and yields also vary dramatically between cultivars within species.
Amaranthus blitum (synonymous with A. lividus):
This species is believed to be native to south or central Europe and is widely dispersed through West Africa, India, South-east Asia, and the Pacific Islands. The plant reaches 30-50 cm in height and its stems are considerably branched.
A dark-seeded strain of A. cruentus is extensively cultivated as a leafy green in West Africa. The plants are mainly un-branched and grow up to 1.5 m tall with long elliptically shaped, coarse leaves.
The dark oblong to elliptic leaves of A. dubius resemble spinach and are considered to be a delicacy in many areas of the Caribbean. The plants grow large, with many side branches. Leaves are harvested through the season, or the entire young plant is harvested. The inflorescence is short and branched.
This species is very variable, often large (0.5-2.0 m tall) with the upper half usually much branched; the leaves vary in shape, colour, and size. Landrace vegetable types have been developed from this species in Mexico.
This species was developed for grain production in Mexico and now is worldwide. It is also an important vegetable species in Mexico with specialized vegetable cultivars.
This prostrate wild species is used heavily in Botswana and other parts of southern and western Africa. It is occasionally cultivated.
Many cultivars of the species A. tricolor are widely dispersed and cultivated throughout Asia and the South Pacific. There is considerable variation in appearance but generally they grow bushy, of medium height with relatively large seed. Varieties in India include Pusa Kiran and Pusa Kirti.
11. Future Prospect of Amaranth:
Amaranth is a versatile crop with a long history of domestication and use. To date only a modest amount of research and plant breeding has been done with this plant, mostly with the grain types. Amaranth is an important plant to diverse human populations around the world, but its use could be greatly enhanced through further breeding and research.
With the diverse collection of germplasm available, rapid progress could be made with a minor investment in screening and breeding projects. Investigations by amaranth researchers and farmers around the world have provided a solid foundation for further development of this valuable plant.