Tropaeolum tuberosum Ruiz and Pav.
Cubio (Col.); Isao, Isau (Bol., Peru, Arg.); Mashua (Peru, Bol.); Navis, Navo (Col.); Ysao (S. Am.).
A herbaceous climber, resembling the garden nasturtium to which
it is closely related, although it is more compact and has smaller flowers. The
stems are green or reddish-green and the leaves show a considerable variation in
form, but are normally 5-20 cm long, peltate, with 3-5 lobes.
The flowers have long peduncles 10-19 cm long; the red calyx forms a spur, sometimes two, and there is considerable variation in the size and shape of the orange petals. The tubers are conical or ellipsoid in shape, generally deeply furrowed, each furrow containing a bud. Over 100 clones are recognised and some authorities consider that two separate species should be recognised: Colombian species, characterised by long deeply furrowed white tubers or white with pink extremes, and numerous rootless; and Peruvian/Bolivian species, with yellow tubers, often with dots and lines on them and without rootless. Chemical examination and cytological evidence have both suggested that there are two distinct types and subspecies status has been suggested, namely T. tuberosum ssp. tuberosum and T. tuberosum ssp. silvestre.
Origin and distribution
The au is native to the high Andes of South America and is confined to this area where it is cultivated in the Andean valleys of Peru and Bolivia.
This crop requires cool and moist conditions and is tolerant of frost; it is normally grown at altitudes of 3 000 m or above, frequently in rotation with ullucu. It is considered to require approximately 12 hours day-length for successful growth.
Material-au is propagated vegetatively from tubers. Method-au
is usually cultivated in small plots on terraces on hillsides; for good yields
it must be kept free from weeds and earthed up.
Field spacing-planting is usually in rows 70-100 cm apart with 40-70 cm between the plants.
The tubers reach maturity in approximately 7 months.
Harvesting and handling
The tubers are dug by hand and are reported to keep better in the fresh state than the other Andean tuber crops, oca and ullucu, with a storage life at ambient temperatures of up to 6 months.
Tubers-au produces small conical or ellipsoidal tubers approximately 5-15 cm long and 3-6 cm wide, with a wide range of colouring which can vary from dirty-white or yellow to red or purple. In the fresh state they have a disagreeable odour.
Yields are reported to lie between 20 and 30 t/ha.
Au tubers are eaten boiled as a vegetable and are said to resemble turnips. In some communities at high altitudes in the Andes, where potatoes and other tubers cannot be grown, au is the staple foodstuff.
It has been suggested that au could be grown for use as a feedingstuff for pigs. In some areas the tubers are valued for their medicinal properties and are used in the treatment of kidney and liver diseases, sores on the skin, and head lice. Traditionally, they are regarded as having anti-aphrodisiacal properties. Planting among other crops is reported to bring protection against nematodes.
Published figures give the composition of the edible portion of the tubers as: energy 218 kJ/100 g; water 86 per cent; protein 1.6 per cent; fat 0.6 per cent; carbohydrate 11 per cent; fibre 0.8 per cent; ash 7 per cent; calcium 7 mg/100 g; iron 1.2 mg/100 g; phosphorus 42 mg/100 g; vitamin A 0.015 mg/100 g; thiamine 0.06 mg/100 g; riboflavin 0.08 mg/100 g; niacin 0.6 mg/100 g; ascorbic acid 67 mg/100 g. The exceptionally high ascorbic acid content is noteworthy.
The plant contains isothiocyanates and thiourea; differences in composition correspond with the cultivated form and wild form and a division into two subspecies, Tropaeolum tuberosum ssp. tuberosum and T. tuberosum ssp. silvestre, has been proposed.
The traditional medicinal uses have been examined:
(i) Effect on reproduction: no effect was found on the male capability of impregnating females, though animals fed extracts of the plant showed a 45 per cent drop of testosterone/dihydrotestosterone in their blood; a similar effect in man would be expected to reduce libido.
(ii) Antibiotic activity: both subspecies contain p-methoxybenzyl glucosinolate, and both show strong antibiotic activity against Candida albicans, Escherichia cold and Staphylococcus albus.
(iii) Kidney diseases: isothiocyanates are diuretic.
(iv) Nematicidal effect: this has been demonstrated and is believed to be due to isothiocyanates.
(v) Head lice: similarly, it is believed that isothiocyanates are effective against head lice.
Production and trade
Little information has been recorded; Peru is stated to have approximately 4 000 ha under cultivation.
Major considerations Au is reported to be grown rather less than formerly, but continues to be an important crop, especially for remote Indian communities where its medicinal value and food value both find favour. A germplasm collection is being made, to be maintained at Cusco and Puna in Peru.
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