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Plantwise Technical Factsheet

quinoa (Chenopodium quinoa)

Description
Quinoa is an annual spring crop. The quinoa plant is 1-1.5 m tall (range 0.5-3 m), terminating in a panicle consisting of small flowers, each producing one seed of 2.5 mg and 1 mm diameter. The most important vegetative characters for the classification of quinoa are plant colour, leaf morphology and growth type, i.e. branching habit. It exhibits a degree of branching, which is controlled by genetic and environmental factors.

The basic colours of quinoa are green, purple and red. Green plants may become white, yellow, orange or red at maturity; purple plants may turn yellow or stay purple on maturing, while the red plants remain red throughout their life. The variability in the colour of the plants and inflorescences of quinoa is due to a wide spectrum of colours present in the vegetative organs and in the perigonium. The pericarp, too, ranges in colour from white, yellow, orange and red, through to brown and black. Wild species often have black pericarp (Jacobsen, 1993).

Quinoa has a vigorous, deep-rooting tap root. Due to a lack of seed dormancy, seedling emergence, including root elongation, occurs quickly in the presence of adequate soil moisture. The tap root divides just below the rootneck giving rise to secondary and tertiary roots. The stem is cylindrical below the rootneck, but angular above with alternating leaf positions, originating from the four sides in turn. Inside the stem there is a fibreless, white to cream-coloured marrow which, in the early stages of growth, is massive and soft but which becomes hollow and spongy as maturity approaches. In contrast, the cortex is firm and compact. The outer stem can be green, green with red axils, green with purple or red stripes, or red (Gandarillas, 1979).

The branches originate from the axils of each leaf on the stem. Their length may vary from just a few centimetres to the same length as the main stem, according to cultivar and environmental conditions. The two extreme types are classified as simple (no long branches) and branched. At low densities, even simple plants will branch to some extent, but commercially the plants will normally be sown at a density that gives no opportunity for this. Branching is undesirable for grain production and is therefore minimized through cultivation techniques (Jacobsen, 1993).

Leaf petioles are long, fine and furrowed. The lower leaf laminas are rhomboidal or triangular, while the upper leaves are triangular or lanceolate. Most often the laminae are plane, but in some types they may be undulating. Leaves possess various morphological adaptations which help them to withstand drought during growth. Among these adaptations are cuticular wax, stomata protected by a thickened epidermis, and papillae on both sides. The young leaves, the stem and the young flowers are normally covered on both sides with white, purple or red stellate papillae.

The most important floral characters for the classification of quinoa are inflorescence type, and size and colour of seed. The inflorescence consists of a number of racemes, which originate from the axils of the whole plant starting from the top. When the branches in the upper part in relation to the lower part of the plant are vigorous and closely spaced, the inflorescences can be easily differentiated from the rest of the plant, and thus it gives the impression of being terminal. Other types may lack any differentiation, as in wild Chenopodium species. Two types of inflorescence exist: glomerulate, where small groups of flowers originate from tertiary axes, and amaranthiforme, originating from secondary axes (Jacobsen, 1993).

All members of the Chenopodiaceae, including the genus Chenopodium, have incomplete flowers without petals. The flowers are hermaphrodite or female. Hermaphrodite flowers vary in size between 2 and 5 mm, and consist of a 5-numbered perigonium, a pistil with an elipsoid ovary and a 2- or 3-branched stigma surrounded by five stames. The female flowers, which are 1-3 mm in size, contain only perigonium and pistil. The flowers can be with or without pedicels.

The fruit is an achene covered by the perigonium, from which it can be removed by rubbing in the dry state. The outer layer of the fruit, consisting of one seed, is the pericarp, which constitute the hull. The pericarp of the fruit contains saponins, which are compounds widely distributed throughout the plant kingdom, being reported in more than 500 species. Saponins may exert both negative effects due to haemolytic activity and bitterness, and a positive effect, due to cholesterol-binding ability (Jacobsen et al., 2000a). Saponin act as a general defense agent towards fungi, insect pests and birds.

Just underneath the pericarp there is a thin episperm. The embryo, which constitutes the cotyledon and the root, surrounds the major part of the mostly white seed perisperm underneath the pericarp and episperm. The perisperm, which is the storage organ of quinoa seeds, and consists primarily of starch, derives from the nucella and therefore being diploid. The many different colours, present in the inflorescences of quinoa, are caused by the colouration of the perigonium, the pericarp and the episperm.

Seeds may be conical, cylindrical or elipsoidal in shape (Quispe et al., 1976), and vary in size from large (2.2-2.6 mm), medium (1.8-2.1 mm) to small <1.8 mm). Seed weight ranges from 2 to 6 mg. The seed can have a sharp or a rounded border, which may be used as a taxonomic character. With few exceptions all the cultivars of quinoa have sharp borders, while the wild Chenopodium species have rounded borders.

The daylength-neutral cultivars from southern Chile all have fruit or seed of the small-seeded, yellow, nutty, hard-pericarp type. Cultivars of the larger-seeded short-day types from Colombia, Ecuador, Peru and Bolivia have a neutral flavour and a soft, easily removable pericarp (Jacobsen, 1993).

The developmental stages has been defined according to Jacobsen and Stølen (1993).
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