Genetic Treasure Trove Revealed in India’s Amaranth Collection

Amaranth has fed people for thousands of years, yet it has long lived in the shadow of staple crops such as rice, wheat and maize. Now a comprehensive genetic survey of Indian amaranth germplasm suggests that this leafy vegetable, often dismissed as a weed or a poor farmer’s green, harbours a wealth of structured variation that breeders can exploit. A research team led by Ajay Kumar Sharma of the ICAR-Indian Institute of Vegetable Research in Varanasi, working with colleagues at Banda University of Agriculture and Technology and the ICAR-Indian Institute of Horticultural Research, examined 96 Amaranthus genotypes from across India, the recognised centre of diversity for the genus. Their study, published in the Indian Journal of Genetics and Plant Breeding, combined classical field descriptions with DNA-based molecular markers to build one of the most detailed pictures yet of the country’s amaranth diversity.

The fieldwork relied on an augmented block design, a statistical layout that allows large numbers of genetically distinct accessions to be evaluated even when seed or planting material is limited. The researchers scored 20 morphological descriptors covering traits that farmers and consumers actually notice: leaf shape and colour, stem pigmentation, petiole characteristics and the colour patterns of the flowering shoots. Every one of the 20 traits showed a wide range of variation across the collection. Some of what the team found was genuinely unusual. Alongside the familiar green-leaved types, the germplasm included novel leaf shapes, stems in white and pink, striking petiole pigmentation and distinct inflorescence colour patterns that had not previously been catalogued in Indian material at this scale.

To quantify that visual diversity, the team turned to the Shannon-Weaver index, a measure borrowed from information theory that ecologists and geneticists use to describe how evenly traits are distributed within a collection. Values in the study ranged from 0.00, meaning no variation at a given descriptor, to 1.48, indicating near-maximal diversity for a trait scored across many categories. Eleven of the traits showed statistically significant morphological variation, confirming that the apparent visual differences among accessions were not random noise but genuine, heritable diversity. For breeders, such qualitative descriptors matter because they are easy to score in the field, they often mark traits with market value, and they can serve as anchors when distinguishing varieties for registration and protection.

Morphology alone, however, can be misleading. Visible traits are shaped by environment as much as by genes, and closely related plants can look alike while carrying very different DNA. So the team profiled the same 96 genotypes with two classes of molecular markers: inter-simple sequence repeats, or ISSRs, and simple sequence repeats, or SSRs. Both target the short, tandemly repeated DNA motifs scattered through plant genomes. ISSR markers use a single primer designed to anchor on one microsatellite and amplify the stretch of DNA between neighbouring repeats, producing dominant fingerprints. SSR markers, by contrast, amplify specific microsatellite loci flanked by known sequences, and because they are co-dominant they can distinguish homozygotes from heterozygotes. Of the 13 ISSR primers tested, six proved polymorphic, and of the 22 SSR markers screened, nine were polymorphic, giving the researchers a solid panel for comparing genotypes across the collection.

The molecular data told a story that the field observations alone could not. Within individual populations, genetic diversity was low, with an expected heterozygosity among subpopulations, denoted Hs, of just 0.15. But when diversity was measured across the whole set of populations, total genetic diversity, Ht, rose to 0.26. That gap is the signature of strong population structuring: the variation exists, but it is partitioned among groups rather than mixed within them. A differentiation statistic, Gst, of 0.42 confirmed moderate-to-high separation between populations, and an estimated gene flow, Nm, of only 0.34 indicated that alleles rarely move from one group to another. In practical terms, the Indian amaranth collection is not a single blended pool but a set of partially isolated lineages, each carrying its own slice of the species’ genetic heritage.

Two complementary ordination and clustering approaches reinforced that picture. Principal coordinate analysis, which compresses pairwise genetic distances into a few visual axes, revealed substantial overall variation, partial clustering of accessions from the same populations and clear evidence of admixture, meaning some genotypes carry ancestry from more than one group. Marker-based clustering then divided the entire collection into five clusters, while a formal population structure analysis, of the kind pioneered by Pritchard and colleagues, identified four admixed subpopulations. The fact that different methods converged on a similar number of groups, while still detecting individuals of mixed ancestry, suggests the structure is real but porous, the result of historical seed exchange, overlapping cultivation and the outcrossing tendencies of the genus.

Why does this matter beyond the herbarium and the molecular lab? Amaranth is a nutritional powerhouse. Its leaves are rich in iron, calcium and vitamins, and the grain types produce gluten-free seeds with an unusually high lysine content, an essential amino acid that cereals typically lack. Reviews have described amaranth as a new-millennium crop of nutraceutical value, and interest in it is growing as consumers seek resilient, nutrient-dense foods. Yet crop improvement depends on having genetically distinct parental lines to cross. If all breeding material derives from a narrow genetic base, gains from selection stall and vulnerability to pests and diseases rises. The new study demonstrates that Indian germplasm contains exactly the kind of structured, exploitable variation that breeding programmes need.

The population structure revealed by the markers offers a practical roadmap. Breeders selecting parents for crossing schemes can now choose lines from different clusters or subpopulations to maximise heterosis, the hybrid vigour that often appears when divergent lineages are combined. Conversely, the low gene flow estimate warns that desirable alleles confined to one group will not spread on their own; deliberate introgression will be required. The rare phenotypes documented in the field, from pink stems to novel leaf shapes, could serve as visible markers in breeding programmes aimed at ornamental or specialty markets, while the quantitative diversity indices identify which descriptors are most informative for future germplasm characterisation.

The study also adds to a growing global literature on amaranth genetics. Earlier work had used ISSR markers to assess grain amaranth in India, SSR markers to profile core collections and single nucleotide polymorphisms to study Peruvian amaranth landraces. What distinguishes the new analysis is its dual approach at scale, pairing a full suite of morphological descriptors with both ISSR and SSR panels on a single large collection, and its focus on India, the crop’s centre of diversity. The work formed part of a doctoral programme at the Varanasi institute and was supported by the Indian Council of Agricultural Research, reflecting a broader national effort to characterise and conserve underutilised vegetable crops before their wild and traditional diversity erodes.

For a genus that includes both cherished vegetables and notorious weeds, the message of this study is that amaranth’s genetic resources are neither uniform nor random. They are organised into discernible populations, laced with rare and beautiful phenotypes, and accessible to any breeder with the right markers and crossing plan. As climate stress pushes farmers toward hardy, fast-growing greens, the structured diversity documented across these 96 Indian genotypes may prove to be one of the most valuable untapped assets in the vegetable world, waiting in plain sight in fields and markets across the subcontinent.

Subject of Research: Genetic diversity characterization of Indian Amaranthus germplasm using morphological descriptors and ISSR and SSR molecular markers

Article Title: Characterization of Genetic Diversity in Amaranthus Species Using Morpho-Molecular Markers

Article References: Sharma, A. K., Sagar, V., Dwivedi, S. V., Devi, J., Neetu, Tiwari, S. K., Singh, S. K., Rai, N., Kumar, R., & Behera, T. K. (2026). Characterization of Genetic Diversity in Amaranthus Species Using Morpho-Molecular Markers. Indian Journal of Genetics and Plant Breeding, 86(2), 224-240. https://doi.org/10.1007/s44489-026-00011-6

Image Credits: AI Generated

DOI: 10.1007/s44489-026-00011-6

Keywords: Amaranthus, genetic diversity, germplasm, ISSR markers, SSR markers, population structure, plant breeding, leafy vegetable, morphological descriptors, Shannon-Weaver index, India, crop improvement