Morphological Assessment of Cultivated and Wild Amaranth Species Diversity

Amaranthus L. is genus of C4 dicotyledonous herbaceous plants comprising approximately 70 species, with three subgenera, which contains both cultivated and wild types, where cultivated ones are used for food grains, leafy vegetables, potential forages and ornamentals. Grain amaranth are pseudocereals from three species domesticated in North and South America and are notable for containing high amount of protein and minerals and balanced amino acid in their small seeds. Genetic diversity analysis of amaranths is important for development of core set of germplasm with widely diverse population and effective utilization of plant genetic resources. In this study, we evaluated a germplasm collection of 260 amaranth accessions from United State Department of Agriculture (USDA) and 33 accessions from Seed Savers' Exchange (SSE). We evaluated morphological traits like blade pigmentation, blade shape, petiole pigmentation, branching index, flower color, stem color, inflorescence density, inflorescence shape, terminal inflorescence attitude, plant height and yield characteristics across all 293 accessions. We compared clustering within the USDA and SSE collection and across both collections. Data analysis of morphological data showed significant difference of petiole pigmentation, stem color, blade pigmentation, blade shape and flower color across different clusters of accessions of USDA unlike among different clusters of SSE where we found significant difference of only blade pigmentation, blade shape and flower color. The relationship depicted by neighbor-joining dendogram using the morphological markers was consistent with some but not all of the differences observed between species. Some divisions were found between cultivated and weedy amaranths that was substantiated by morphological characteristics but no separation of South and Central American species was observed. Substantial phenotypic plasticity limits the use of morphological analysis for phylogenetic analysis but does show that important morphological traits such as inflorescence type and plant architecture can cross species boundaries. Similarly, color variants for leaves, flowers and seeds are not exclusive to one cluster in our study nor to one species and can be used widely for breeding any of the cultigens, but not to species identification. Our findings will help in germplasm conservation of grain amaranths and facilitate in this crop's improvement. It will also help on developing effective breeding programs involving different plant characteristics and morphological traits of Amaranths.