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Vol. 5 No. 4 - October 1999

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 Ám) 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.

This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.

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