The drought resistance of quinoa is attributed to morphological characters such as a deep, extensively ramified root system, reduction of leaf area through leaf dropping, small and thick walled cells adapted to large losses of water, and the presence of vesicles containing calcium oxalate that are hygroscopic in nature and reduce transpiration (Canahua, 1977; Jensen et al., 2000; Jacobsen et al., 2003a). Physiological characteristics indicating drought resistance include low osmotic potential, low turgid weight/dry weight ratio, low elasticity and an ability to maintain positive turgor even at low leaf water potentials (Andersen et al., 1996). It has been observed that the stomatal conductance of quinoa remains relatively stable with low but ongoing gas exchange under very dry conditions and low leaf water potentials (Vacher, 1998). Quinoa maintains high leaf water use efficiency to compensate for the decrease in stomatal conductance and thus optimizes carbon gain with a minimization of water losses. Jensen et al. (2000) studied the effects of soil drying on leaf water relations and gas exchange in quinoa. The study showed that high net photosynthesis and specific leaf area (SLA) values during early vegetative growth resulted in early vigour of the plant, supporting early water uptake and tolerance to a following drought. The leaf water relations were characterized by low osmotic potentials and low turgid weight/dry weight ratios during later growth stages sustaining a potential gradient for water uptake and turgor maintenance under high evaporation demands. Garcia et al. (2003) calculated the seasonal yield response factor (Ky) for quinoa and observed that it was lower than that of groundnut and cotton. This low Ky value for quinoa indicated that a minor drought stress does not result in a large yield decrease.
The frost resistance of quinoa has been recognized for many years (Rea et al., 1979). The species exhibits 100% germination even at 2°C and no serious effect on the plant at temperatures close to −3°C (Bois et al., 2006). The main mechanism for the frost resistance of quinoa seems to be that it tolerates ice formation in the cell walls and the subsequent dehydration of the cells, without suffering irreversible damage (Jacobsen et al., 2003a). The presence of soluble sugars, such as fructans, sucrose and dehydrins, may be good indicators of frost tolerance in quinoa (Jacobsen et al., 2003a, 2005). Results have shown that quinoa seeds germinate rapidly even at low temperatures, with the base temperature for germination lower than 0°C for 9 cultivars out of 10 (Bois et al., 2006).
Hail and snow are sporadic and localized in the Andean region and sometimes causes irreversible damage, especially when the crop is near to maturity (Jacobsen et al., 2003a). Cultivars of quinoa exist with good tolerance to hail, mainly due to a minor leaf angle and greater thickness and resistance of leaves and stem. Flooding occasionally occurs in rainy years on flat areas and produces root rot, greatly reducing yield (Jacobsen et al., 2003a). Wind affects crop productivity by causing plants to fall, especially in the arid region of the altiplano and in some inter-Andean valleys. Wind is also responsible for erosion and drying of soil and plants. When quinoa is cultivated in deserts and hot areas, high temperatures can cause flowers to abort and the death of pollen (Jacobsen et al., 2003a). Fortunately, the genetic variability of quinoa makes it possible to select cultivars with greater tolerance to each of these environmental factors.
1.3.3 Economic uses
Quinoa has diverse uses. It is considered as one of the best leaf protein concentrate sources and so has the potential as a protein substitute for food and fodder and in the pharmaceutical industry. The whole plant can also be used as green fodder for cattle, sheep, pigs, horses and poultry. Results have indicated that up to 150 g/kg unprocessed or dehulled quinoa seed could be included in broiler feed (Jacobsen et al., 1997). This incorporation of quinoa in poultry feeds can greatly benefit the poultry industry. The seeds can be eaten as a rice replacement, as a hot breakfast cereal or can be boiled in water to make infant cereal food (Bhargava et al., 2006a). Quinoa seeds can be ground and used as flour, or sprouted, and can even be popped like popcorn. In Peru and Bolivia, quinoa flakes, tortillas, pancakes and puffed grains are produced commercially (Popenoe et al., 1989). Quinoa flour in combination with wheat flour or corn meal is used in making biscuits, bread and processed food (Bhargava et al., 2006a). There are numerous recipes for about 100 preparations, including tamales, huancaína sauce, leaf salad, pickled quinoa ears, soups and casseroles, stews, torrejas, pastries, sweets and desserts, and soft and fermented hot and cold beverages, as well as breads, biscuits and pancakes, which contain 15–20% quinoa flour. The flour has good gelation property, water absorption capacity, emulsion capacity and stability (Oshodi et al., 1999). The high water absorptivity may be used in the formulation of some foods such as sausages, dough, processed cheese, soups and baked products (Oshodi et al., 1999). Quantitative analysis of the sugar content and chemical composition of seed flour of quinoa has shown that it has a high proportion of D-xylose (120 mg/100 g), and maltose (101 mg/100 g), and a low content of glucose (19 mg/100 g) and fructose (19.6 mg/100 g) (Ogungbenle, 2003). Thus, quinoa could be effectively utilized in the beverage industry for the preparation of malted drink formulations. It can be fermented to make beer, or used to feed livestock (Galwey, 1989). Solid-state fermentation of quinoa with Rhizopus oligosporus Saito provides a good-quality tempeh (Valencia-Chamorro, 2003). Quinoa milk, a high quality and nutritive product, may have the potential for consumption as milk or as an ingredient of milky products (Jacobsen et al., 2003b). This tasty and healthy product is of particular importance for people who are unable to digest casein or animal lactose.
Quinoa starch can be used for specialized industrial applications because of its small granules and high viscosity (Galwey et al., 1990). Starches having small-sized granules could serve as dusting starches in cosmetics and rubber tyre mould release agents (Bhargava et al., 2006a). Quinoa starch also has potential for utilization as biodegradable fillers in low-density polyethylene (LDPE) films (Ahamed et al., 1996a). However, this aspect needs more investigation for effective utilization in the food, pharmaceutical and textile industries. Because of its mechanical properties, quinoa starch can be utilized in the manufacture of carrier bags, where tensile strength is important. Studies on freeze–thaw stability of quinoa starch have shown that its paste is resistant to retrogradation, suggesting applications in frozen and emulsion type food products (Ahamed et al., 1996b; Bhargava et al., 2006a). Another potential use of the plant could be in cloth dyeing and food preparation because of the presence of betalains, a natural colorant (Jacobsen et al., 2003b).
Quinoa has been evaluated as a food with excellent nutritional characteristics by the National Research Council and the National Aeronautics and Space Administration (NASA) (Schlick and Bubenheim, 1996). The plant is being considered as a potential crop for NASA’s Controlled Ecological Life Support System (CELSS), which aims to use plants to remove carbon dioxide from the atmosphere and generate food, oxygen and water for the crew of long-term space missions (Schlick and Bubenheim, 1996).
1.3.4 Medicinal importance
The use of quinoa for medicinal purposes has also been reported (Mujica, 1994). The plant is reportedly used in inflammation, as an analgesic and as a disinfectant of the urinary tract. It is also used in fractures and internal haemorrhaging and as an insect repellent (Mujica, 1994). The presence of glycine betaine, trigonelline and their derivatives has been reported in the plant (Jancurova et al., 2009). In humans, glycine betaine can be readily absorbed through dietary intake or endogenously synthesized in the liver through choline catabolism. The concentration of glycine betaine in human blood plasma is highly regulated. Its concentrations are lower in patients with renal disease, and its urinary excretion is elevated