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Amaranthus :
Evolution, Genetic Resources and Utilization
By:
Mohinder Pal
The
genus
Amaranthus
is rather unique in having species which are used for grain, vegetable and
ornamental purposes. Recently the potential of microcrystalline (1-3 µm) starch
granules for possible replacement of talc in the cosmetic industry and edible
dyes has emerged. The major attributes of amaranths are their adaptability to a
wide range of climatic and soil conditions, superior nutritional quality of
grain with high protein (12-19%) and complementary amino acid profiles (lysine
5-7%), easily digestible starch, presence of cholesterol lowering fractions in
the seed oil and high carotene (pro-vitamin A) contents in the leaves. The
grain amaranth ('ramdana', 'marcha', 'ganhar', lathe') considered by many as
the crop of the future has been associated with man since prehistoric times
(4,800 BC). The most common use in the major regions of its cultivation (Peru,
Bolivia, Ecuador, Mexico, India, Nepal and Bhutan) is in the form of cakes or
balls (laddoos) prepared by binding the popped seed in jaggery/sugar. The
vegetable amaranths are used as pot herbs in most tropical countries of the
world. While the related foliage ornamental types add colour to the otherwise
drab garden surroundings in summer months.
The grain
amaranths constitute a group of pseudocereals which have a long history of
domestication and cultivation (7,000 years). These are important source form of
subsidiary food especially in the Himalayan Valleys because of their high
nutritive value and excellent amino acid composition. The vegetable amaranths
are used all over India as pot herbs and are rich in Vitamin A (2,000 to
11,0000 iu/ 100 gms) and leaf protein (2-3%).
Detailed
basic studies, have provided a very clear picture of evolutionary dynamics of
this group of plants. This was possible by undertaking a systematic programme
involving breeding systems, intra-interspecific hybridization, dilled analysis
on a very large amount of plant material secured from all over the world, in
order to decipher not only the genetic relationships but also the size of the
gene pool available for their improvement. These studies have revealed a very
interesting series of reproductive barriers like unidirectional incompatability,
male sterility, hybrid sterility and 'virus' like syndromes, the last being
unique and unravelled for the first time in this group of plants. The
cytogenetic investigation of F1 and F2 progenies of the
dibasic interspecific crosses involving A. hybridus (2n=16), A.
hypochondriacus (2n=16), A.
cruentus
(2n=17) and A.
retroflexus
(n=17) have shown that x=16 is ancestral and x=17 derived through primary
trisomy. A close genetic homology has been found between the progenitors like.
A. hybridus and A. quitensis on the one hand and between them and
their respective domesticates-namely A. hypochondriacus -cruentus and A.
caudatus edulis.
The
domesticates and the progenitor species thus constitute essentially a single
'gene pool' in which despite be achieved through the wild progenitor species.
The discovery for the first time of the existence of a wild species viz.
Amaranthus retroflexus L.
in the
Ladakh and adjacent regions of India and evaluation of its cytogenetic
relationship with the cultivated grain amaranth species viz.
A. cruentus
L. (n=17) is of special significance in as much as the fertility shown by the
hybrid could be used for evolving a grain amaranth crop for cold dry desert
regions of India and other adjacent countries. Earlier Amaranthus
retroflexus
was not
considered a close relative of grain species and thus the study has also helped
in broadening the 'gene pool' of grain amaranths.
The foliage
of sixty one lines comprising both the grain and vegetable amaranths referable
to 10 species were evaluated for carotenoid, protein, nitrate and oxalate
contents (fresh weight). Carotenoid varied from 9.0 to 20.0 mg/100 g in
vegetable and 6.0 to 20.0 mg/100 g in the leaves of grain type. Variation with
leaf protein was found to be 1.4 to 3.0%, 1.5 to 4.3%, nitrate 0.18 to 0.80%,
0.41 to 0.92% and oxalate 0.51 to 1.92% and 0.3 to 1.65% in vegetable and grain
types respectively. The results were compared with the other cereals and leaf
vegetables. Protein and amino acid composition was analysed in 19 lines of
Amaranthus hypochondriacus
cultivated
solely for grains in India. Variation of protein was from 8.9 to 15.7% and
lysine 3.8 to 5.5%. Seed protein and amino acid composition over a ten year
period, in grain species A.
hypochondriacus
revealed
stability for these features. Considerable variation as revealed by the present
studies is of significance for developing nutritionally superior lines both in
the vegetable and grain amaranths.
The National
Botanical Research Institute of India (NBRI) has built up perhaps, one of the
best qualitative collections-of amaranth 'germplasm' in the world, comprising
nearly 400 accessions, referable to 20 species,
of which nearly half belong to the grain types. The most precious amaranth 'germplasm'
in NBRI's collection is that of wild progenitor species of both the grain and
vegetable domesticates as determined through an extensive hybridization
programme. This could prove to be of immense value in developing varieties with
desirable attributes for use under different agroclimatic regions in the
developing countries.
The basic
studies carried out at NBRI constitute important steps in the genetic upgrading
of vegetable and grain amaranths to meet the dietary requirements of the
populations in the developing countries. However, for optimum utilization of
the multidimentional potential of amaranths efforts in many areas especially in
food processing, commodity/product development and marketing are needed.
Dr.
Mohinder Pal is a retired scientist of National Botanical Research Institute,
Lucknow, India. |
