Abstract
The genus Chenopodium comprises about 150 species distributed all around the world and over a wide range of environments. In South America, differents species, either cultivated as C. quinoa Willd. and C. pallidicaule Aellen, or wild as C. hircinum Schrader, are distributed over pedoclimatic gradients from the sea level in Chile, up to an altitude of 4000 m in the altiplano of Bolivia and Peru, on soils more or less thick and rich in nutrients, and under climates from tropical humid to arid and cold. These species are phylogenetically related, and it is generally admitted that C. quinoa was domesticated from C. hircinum and that part of its genome comes from C. pallidicaule. Their wide distribution in natural and crop ecosystems and their more or less strong tolerance to environmental constraints, make this group of species an interesting model for examining the diversity of responses of the plants, in particular facing a low disponibility of resources in the soil. As all the water necessary for the life of the pass through the root system, we focused our interest in the intra- and interspecific variations in the root growth and architecture, and their responses to the water deficit, with the hypothesis that plants from arid habitats or from low-input agrosystems, developed root traits that allowed them to increase the acquisition of resources in the soil. To test this hypothesis we compared the root growth and development in plants of two ecotypes of C. quinoa from more or less arid regions, and of populations of C. pallidicaule and C. hircinum, placed under non-limiting or water deficit growth conditions, in pots and in rhizotrons. The main results of this research show that, despite large differences in biomass production and morphology of the aerial plant part, the studied populations showed the same root typology. They differed by several traits of root architecture and morphology which control the capacity of the plant to explore and exploit the soil resources. Some of these traits, such as the taproot elongation rate, showed a high plasticity in response to the water deficit. Other traits, like the specific root length, were less plastic but showed large interspecific differences. These variations in plant root architecture conforms adaptive syndromes that favor the plant survival in the most limiting environments. Key words : Chenopodium quinoa, Chenopodium hircinum, Chenopodium pallidicaule, root system, root architecture, topological index, ontogeny, rhizotron, root elongation, plant growth analysis, cultivated species, wild species, root growth, root morphology.