Pachyrhizus erosus

Common name: Yam bean

Other common names: Chop suey bean, Manioc bean, Mexican turnip

Names in non-English languages: Philippines French India Spanish Malaysia Thailand German China

Description

Jicama or Yam Bean is a leguminous vine originating in Central American, its natural range extending across Mexico, Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica. It is widely cultivated for its tubers, which are eaten as a vegetable, mainly in its native range and in the Philippines, where it was introduced long ago.

It is a fast-growing vine, producing woody stems at the base, above which grow herbaceous angular stems up to 5 m (16 ft) long covered with fine brown hairs. They have a vining and twining habit, climbing up on any structure they come into contact with or, in the absence of a structure, trail along the ground.

The leaves are trifoliate, each made up of three dark green, broadly heart-shaped leaflets up to 20 cm (8 in) wide and almost as long.

Flowering is induced by shortening days from the end of summer to autumn, with white, pink or purple pea-like flowers held in erect clusters, arising at nodes along the vine. With the commencement of flowering, vegetative growth slows and the storage roots swell, forming large tubers. The tubers develop a turnip shape with thin, pale brown skin and crispy white flesh.

The flowers are followed by flat, ribbed seedpods covered with irritant hairs, becoming hairless when mature. They are up to 14 cm (5.5 in) long and enclose six to twelve flat, squarish seed.

Use

The main interest in the plant is its tubers which are eaten as a vegetable. A single tuber can weigh in excess of 3 kgs (6.6 lbs), though overly large tubers tend to become fibrous, losing their crispness and sweetness.

The tubers are washed and the skin peeled off, leaving only the crispy white flesh which does not discolour upon exposure to air. This has a high water content and can be eaten raw or cooked. In its raw form, it makes a good substitute for water chestnuts used in Asia cooking and has become an essential ingredient in Malaysian spring rolls.

In its native region, it is commonly sliced into strips, sprinkled with chilli, salt and lime juice and eaten as a snack. It is eaten in a similar way in Thailand, but with sugar added to the chilli and salt mixture to create a dry dip known locally as 'phrik ka kriea'. It can also be coarsely grated and added to salads or can be diced and pickled. The texture is crunchy or crispy and the taste subtlety sweet, reminding somewhat of apple.

Because of its mild flavour, it can be combined with a range of flavouring ingredients and maintains its crunchy texture even after cooking, suitably replacing water chestnuts or bamboo shoots in Asian stir-fries. Thinly sliced, it can be deep-fried to make chips or crisps, or can be cut into batons, seasoned and baked to make Jicama french fries.

Rotenone contained in the mature seed has insecticidal properties. It is a colourless, odourless, crystalline poison that is highly toxic to cold-blooded animals, including insects and worms, and has been widely used as an agricultural insecticide.

Health use

Jicama tubers are a low-calorie food, comprising less than 10% carbohydrates and very little fat. They are considered a good food for persons with adult diabetes because the carbohydrates in them are in the form of inulin, a natural compound produced at the expense of starch with minimal effect on blood sugar levels. Inulin is also thought to play a part in lowering blood cholesterol levels.

Climate

Grows naturally in moderately humid subtropical and tropical climates, generally in areas with annual lows of 12 to 25 °C, annual highs of 26 to 35 °C and annual rainfall of 900 to 2500 mm.

Jicama is also cultivated with irrigation in much drier areas, such as Dakar, in Senegal, which receives around 500 mm annual rainfall and has a long dry season lasting up to 9 months.

Growing

New plants can be started from seed or tubers. However, seed-raised plants take from five to nine months to produce harvestable tubers whereas tuber-raised plants take only three to five months to do the same.

The soil needs to be light and free-draining so that tuber growth is not restricted and fungal disease is not encouraged. Suitable soils are free-draining loams and sands of a moderately acid to neutral nature, generally with a pH of 5.0 to 7.5 and planting sites need to have full to partial sun exposure.

Planting is done mostly on raised beds enriched with organic matter and the vines provided with stakes or stout trellises to climb up on, which is essential for good vine growth and tuber production.

Tubers start forming after flowering is initiated (by shortening days) and at the same time vegetative growth declines, with most of the plant's energy diverted to tuber growth. In temperate and subtropical regions with long summer days, vegetative growth continues at the expense of tuber growth, making such regions generally unsuitable for cultivating Jicama.

The best quality tubers weigh between 1 and 2 kgs ( 2 and 4.5 lbs) and yields in commercial operations range from 7,000 to 10,000 kgs per hectare, or the equivalent of 6,200 to 8,900 lbs per acre.

Problem features

The above-ground parts, particularly the leaves and mature seed, contain the glycosides pachyrrhizid and pachyrrhizine as well as various saponins, which may be toxic to humans.

It is recorded as naturalised in some countries and as a weed in Florida and Australia but there does not appear to be any record of it anywhere as a serious weed or invasive species.

Where it will grow

With irrigation or groundwater

References

Books

  • Adams, C. D. 1972, Flowering plants of Jamaica, University of the West Indies, Mona, Greater Kingston

  • Allen, O. N. & Allen, E. K. 1981, The Leguminosae : a source book of characteristics, uses, and nodulation, University of Wisconsin Press, Madison, Wisconsin

  • Bladholm, L. 1999, The Asian grocery store demystified, 1st edition, Renaissance Books, Los Angeles, California

  • Brady, G. S. & Clauser, H. R & Vaccari, J. A. 2002, Materials handbook : an encyclopedia for managers, technical professionals, purchasing and production managers, technicians and supervisors, 15th ed., McGraw-Hill, New York

  • Duke, J. A. 1981, Handbook of legumes of world economic importance, Plenum Press, New York

  • Editors of Sunset Magazine 2012, The New Western Garden Book: The Ultimate Gardening Guide, 9th edition, Sunset Publishing Corporation, California

  • Hanson, B. 2007, Buried treasures : tasty tubers of the world : how to grown and enjoy root vegetables, tubers, rhizomes, and corms, Brooklyn Botanic Garden, Brooklyn, New York

  • Jacquat, C. & Bertossa, G. 1990, Plants from the markets of Thailand : descriptions and uses of 241 wild and cultivated plants, with 341 colour photographs, Editions Duang Kamol, Bangkok

  • Kochhar, S. L 1998, Economic botany in the tropics, 2nd ed, Macmillan India, Delhi

  • Macmillan, H. F. 1943, Tropical planting and gardening : with special reference to Ceylon, 5th ed, Macmillan Publishing, London

  • Morgan, D. & Achilleos, A. 2012, Roots : the definitive compendium with more than 225 recipes, Chronicle Books, San Francisco

  • National Research Council (Board on Science and Technology for International Development) 1979, Tropical legumes : resources for the future, The National Academies Press, Washington D. C.

  • National Research Council (Board on Science and Technology for International Development) 1989, Lost Crops of the Incas: Little-Known Plants of the Andes with Promise for Worldwide Cultivation, The National Academies Press, Washington D. C.

  • Norrington, L. & Campbell, C. 2001, Tropical food gardens : a guide to growing fruit, herbs and vegetables in tropical and sub-tropical climates, Bloomings Books, Hawthorn, Victoria

  • Perkins, K. D. & Payne, W. 1981, Guide to the poisonous and irritant plants of Florida, Florida Cooperative Extension Service, Gainesville, Florida

  • Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne

  • Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

  • Rubatzky, V. E. & Yamaguchi, M. 1997, World vegetables : principles, production, and nutritive values, 2nd ed., Chapman & Hall, New York

  • Tindall, H. D 1983, Vegetables in the Tropics, Macmillan Press, London

Articles, Journals, Reports and Working Papers

  • International Plant Genetic Resources Institute (IPGRI) 1996 to 1998, Promoting the conservation and use of underutilized and neglected crops (Series of 24 publications), IPGRI, Rome

© All rights reserved Iplantz 2019