Lupinus mutabilis is a species of lupin grown in the Andes, mainly for its edible bean. Vernacular names include tarwi(tarhui), chocho, altramuz, Andean lupin, South American lupin, Peruvian field lupin, and pearl lupin. Its nutrient-rich seeds are high in protein, as well as a good source for cooking oil. However, their bitter taste has made L. mutabilis relatively unknown outside the Andes, though modern technology makes it easier to remove the bitter alkaloids.
The origin of L. mutabilis has been identified in the Andean region of Ecuador, Peru and Bolivia. In this area, the greatest genetic variability in the world was found. The plant has been domesticated for more than 1500 years, mostly because of its high protein content.
L. mutabilis is an annual plant. The stem is hollow and highly branched. Plant height reaches from 0.5 to 2.8 meters, depending on the environmental conditions and the genomic properties. Due to the high vegetative growth, species from northern South America are taller than species from the southern Andean region. The genome contains 2n = 48 chromosomes and there is a high genomic variation, which leads to big differences in morphology. Several architectural types of L. mutabilis exist. Most common is the branching in V-form, this type has the highest biomass production. The basal branching type has the positive feature that its infructescence is at the same level. This species is preferably promoted because of its early ripening, stability and the homogeny seed quality.
The fruit is a 5 to 12 cm (2.0-4.7 in) long pod, depending on the amount of seed. One pod contains on average 2-3 seeds, but can have up to 9 seeds per pod. The thousand-seed weight (TSW) is around 200 g. Leaves are palmate and have a typical appearance: one leaf is divided in five to twelve leaflets, which have an oval or lanceolate form. The form is typical for Faboideaes. The corolla reaches 1 to 2 cm (0.39-0.79 in) and contains five petals. Variation in coloration is high and reaches from white to purple. The white coloration is recessive to purple. L. mutabilis has a strong taproot reaching 3 m length. Like all Leguminosae secondary roots build nodules containing bacteria for nitrogen fixation.
The growing cycle varies from 150 to 360 days, depending on the genotype, altitude and environmental conditions. Phenological phases are: emergence, first true leaf, formation of the raceme on the central stem, flowering, podding, pod ripening, and physiological maturity.
The bone-white seed contains more than 40% protein and 20% fat and has been used as a food by Andean people since ancient times, especially in soups, stews, salads and by itself mixed with boiled maize. Like other legumes, its protein is rich in the essential amino acid lysine. The distribution of essential fatty acids is about 28% linoleic acid (omega-6) and 2% linolenic acid (omega-3). It has a soft seed coat that makes for easy cooking. It may not have been more widely used because of its bitter taste, due to the alkaloid content. It contains unusually high amounts of sparteine, which make up nearly half of its alkaloid content. However, the alkaloids are water-soluble and can be removed by soaking the seeds for some days in water. It is also possible to remove the alkaloids by denaturation with heat treatment.
L. mutabilis contains 42% of protein and 18% fat in average. The high fat content has allowed commercial oil pressing. The protein digestibility and nutritional value are reportedly similar to those in soybeans.
Contents in the seed:
|Protein||42.6||37.7 - 49.7|
|Oil||18.7||12.8 - 22.2|
|Fibre||6.27||4.29 - 7.51|
|Ash||3.69||3.10 - 4.24|
|Carbohydrates||27.3||23.7 - 29.9|
|Alkaloids||3.26||2.56 - 4.14|
L. mutabilis is able to fix nitrogen from the air. Therefore, succeeding cultures can profit from 60 to 140 kg (310 lb) of nitrogen per hectare. Incorporation in the flowering stage leads to a higher quantity of organic matter and to an improved soil structure.
L. mutabilis is a crop for cool climates and exists mainly in valleys at high altitudes, such as the Andes at tropical latitudes. The crop can be grown at an altitude that ranges from 800 to 3000 m. The crop withstands exceptional levels of drought. Mature plants are resistant to frost, whereas seedlings are sensitive to low temperatures.
In traditional farming practices minimum tilling is done before sowing. 100 to 120 kg (220-260 lb) unselected seeds per hectare is sown.
Improved cultivation practices:
It is recommended to apply 80 kg (180 lb) phosphorus and 60 kg (130 lb) of potassium as fertilization before sowing. The sowing of 90 kg (200 lb) selected seeds in a distance of 60 to 80 cm (24-31 in), either by hand or by seed drill, follows. Plants germinate fast due to the high fat content in the seeds.
Crop rotation aspects
Early varieties of L. mutabilis, with a growing period of about 150 days, can be cultivated in rotation with potatoes and cereals. Nematode disease of potato can be controlled by alkaloids when cultivated after L. mutabilis.
In traditional farming practices harvest occurs when plants have reached full maturity and the water content of seeds is between 8-12%. From peasant plots average yield is about 500 to 1,000 kg (1,100-2,200 lb) per hectare under suitable conditions yield reaches up to 3,500 kg (7,700 lb) per hectare.
Alkaloids can act as a pesticide but breeding goals aim for a low alkaloid content. Therefore, other disease control methods must be applied. Since ''L. mutabilis'' is a low-input crop, disease control mainly is done by phytosanitary methods. A reduction of soil born saprophytes can be reached by removing dry straw from the field. Instead of green manure the plant residues can be used as fuel. Seed borne diseases can be reduced by translocation of seed production and by the use of certificated seed. If seed production is done by the cultivator, diseases can be controlled by reducing the number of infected seed and by a permanent control of diseases in the field. Another possibility is to treat seed with a fungicide prior to sowing.
Since species with low alkaloid content are already available a further step would be to make them more stable and low alkaloid content is inherited. Other breeding goals are tolerance to diseases and insects, improvement in yield, early maturing and synchronous ripening. Higher resistance could be reached by breeding a variety with high alkaloid content in leaves but not in the seeds.