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An important point is that plant genetic resources have been collected and exchanged for over 10,000 years, and more than 5000 years for quinoas (Planella et al., 2011). As the practice of agriculture spread along with human migrations, genes, genotypes and crop populations were carried by people around the world. What is interesting to note is that each group of farmers who settled in a specific location continued to improve their cultivars in order to suit the specific requirements of their farming practices and the ecology of the environment in which they chose to settle and work. Farmers never stopped developing and improving plants, both in their places of origin and in locations very far away, and as populations became more settled, they began to cultivate the large number of species that are found today.

Agriculture has always been based on access to and exchange of plant genetic resources. Farmers give each other material in order to be able to sow from year to year. Agriculture was never based on the exclusive principles observed today with the extension of property rights over the living world. Through these free exchanges, people traded plants, local landraces and seeds. Through their travels, they brought back exotic species to cultivate alongside their usual plants. Farmers introduced exogenous material to avoid declines in productivity and a degeneration of variety cultivars in their fields.

Before discussing Chenopodium quinoa Willd., we need to consider all the species of the genus Chenopodium (Chenopodiaceae), which includes about 250 species that are mostly colonizing herbaceous annuals occupying large areas in the Americas, Asia and Europe, though some are also suffrutescent and arborescent perennials.

Nowadays, three important species of Chenopodium are in cultivation as food plants: C. pallidicaule Aellen and C. quinoa Willd. in South America and C. nuttalliae Safford in Mexico. Other species of the genus are known to have been important wild food sources in North America. Wild species were also used in Europe for food. This wide use of chenopods for food is not surprising because most species produce large numbers of seeds, which have a high protein content, and the leaves can also be used for human consumption (Risi and Galwey, 1984, 1989).

The economically important species of the genus Chenopodium are:

• C. quinoa (2n = 36) used as a grain crop;

• C. pallidicaule (2n = 18), C. berlandieri subsp. nuttalliae (2n = 36) used for both grain and vegetable; and

• C. album (2n = 18, 36, 54) mainly used as a leafy vegetable and foliage crop, though some Himalayan types are also cultivated for grain.

Using Chenopodium seeds for human consumption is not unique to the Andean region:

• C. berlandieri ssp. nuttalliae, a species similar to C. quinoa, is largely consumed in Mexico for its tender leaves and inflorescences.

• In the Himalayas in India, Nepal, Bhutan and China, farmers cultivate a kind of chenopod (classified as C. album) at altitudes of 1500–3000 m.

• C. album is a widespread weed and was part of the human diet in Europe according to prehistoric human remains found in Tollund (Denmark) and Cheshire (UK).

All of these examples show the importance of the genus Chenopodium and the need for research on the links between species. Phylogenetic relationships between cultivated and related wild taxa have been studied on the basis of allozyme studies, crossability and DNA structuration, but the complex and great morphological, ecological and chromosomal diversity found within the genus complex needs further studies to settle the taxonomic problems.

Quinoa, as a food grain, has been recognized for centuries as an important food crop in the high Andes of South America. Cultivated chenopods, especially C. quinoa, are gaining importance for their outstanding protein quality and high content of a range of minerals and vitamins. The genetic diversity of C. quinoa, with its salt and drought tolerance, offers a wide adaptation for many difficult environments. The very name quinoa in the Quechua and Aymara languages means ‘Mother Grain’. Within South and Central America, two closely related species, Canihua (C. pallidicaule) and Huazontle (C. nuttalliae), are also utilized for food. The descendants of the Inca Empire, 8–10 million Quechua and Aymara Indians, still use quinoa as an important component of their diet.

Quinoa has been cultivated for more than 5000 years in the Andes. Some data report that it was probably domesticated by ancient civilizations at different times and in different geographic zones, including Peru (5000 BC), Chile (3000 BC) and Bolivia (750 BC) (Kadereit et al., 2003). Nowadays, its existence is explained by the transmission of seeds by the Incas to other Chilean aboriginal groups living in distinct agroecological contexts, from the Chilean Altiplano (17°S) to Chiloé Island (42°S) and beyond (47°S, Puerto Rio Tranquilo). However, during the Spanish conquest this crop was strongly discouraged because of its cultural importance and because it was considered a sacred crop by the indigenous people (Ruas et al., 1999).