Contributor: Wanda W. Collins
Copyright © 1995. All Rights Reserved. Quotation from this document should cite and acknowledge the contributor.
- Common Names
- Scientific Names
- Crop Status
- Anti-nutritional factors
- Crop Culture
- Production Practices
- Harvesting and Storing
- Commercial "Seed" Sources
- Key References
- Selected Experts
Spanish: batata, boniato, camote
Species: Ipomoea batatas (L.) Lam.
Cultivated primarily for edible storage roots; vines are used as vegetables in
some parts of the world. Both starchy roots and vines can be used as animal
feed or feed supplement. Various products such as candy, pastas, flour, drinks
are produced in local industries.
New World; northwestern South America
A tropical perennial cultivated as an annual in temperate climates; grown in
more than 100
countries in tropical, sub-tropical and temperate climates, it is used as a
major food staple in a few countries, as an alternative staple in many
countries, and as an incidental or luxury addition to the diet in many
countries. It is one of only seven world food crops with an annual production
of more than 100 million metric tons per year ranking thirteenth globally in
production value among agricultural commodities. It is cultivated primarily
for the enlarged edible storage roots which provide high amounts of starch to
staple diets. Use as an export crop is rare and production is usually to meet
local or national needs. Asia accounts for over 80% of world production (most
of that is in China), Africa for about 15% and the rest of the world about 5%.
The US accounts for less than 1% of world production.
Although variation in storage root skin color and flesh color is abundant, two
major types exist which delineate usage. In most developing countries where
sweetpotato is used as a staple or alternative staple food, the type of root
which is produced has white to cream colored flesh and a bland, non-sweet
flavor. It is dry in texture and often has a high dry matter content. The
energy content which it can provide in staple diets depends on the dry matter
content. In contrast, the type most used in developed countries, where use is
normally as a vegetable or dessert, has root flesh color of yellow or deep
orange, moist texture, a very distinct flavor and high sugar content. The
yellow or orange flesh color is directly related to beta-carotene, a precursor
of Vitamin A. Other nutrients supplied by sweetpotato are Vitamin C, iron and
potassium. Protein content is very low in storage roots and does not add
substantially to daily supply of protein.
Sweetpotatoes contain trypsin inhibitors which may reduce ability to utilize
protein if eaten raw. However, trypsin inhibitors do not survive cooking and
are of no consequence in cooked roots.
Sweetpotato is a member of the family Convolvulaceae, Genus Ipomoea,
section Batatas. It the only hexaploid (6x = 90) in this section and its
origin is unknown. Section Batatas continues to undergo revision but contains
approximately 12 other species, most of which are diploid (2n = 30), with a few
tetraploids (4x = 60). Tetraploid sweetpotatoes have been collected in the
wild although rarely. Ipomoea trifida, a diploid, is purported to be
one of the likely progenitors of sweetpotato. Species in section Batatas have
been shown to contain unreduced gametes but the derivation of the hexaploid
sweetpotato remains a mystery. Different theories of the evolution of I.
batatas have been advanced by Japanese researchers, who consider it an
autopolyploid derivative of I. trifida, and American researchers, who
favor an allopolyploid origin involving I. trifida and an unidentified
tetraploid parent. Introgression of traits from related species is normally
prevented by crossing barriers between species. Some success has been reported
through using massive numbers of crosses and embryo culture. However,
introducing genes by this method is still generally not viable in a breeding
program even though a few traits of considerable interest have been identified
in related species.
The major center of diversity for I. batatas is in northwestern South
America (northern Peru, southern Ecuador) but other very important centers of
diversity exist in sub-Saharan Africa, Papua New Guinea, and Indonesia.
Sweetpotato is cultivated as a perennial in tropical and subtropical lowland
agroecologies although it is well adapted to other zones and can be grown over
widely different environments. The crop will grow with temperatures between
15°C and 35°C; however, the lower and higher temperatures have detrimental
effects on yield. Storage roots are sensitive to changes in soil temperature
depending on stage of root development. Sweetpotato responds well to
increasing moisture but is considered a drought-tolerant crop because it is
deep rooted and capable of developing storage roots under very dry conditions.
Excessive moisture inhibits storage root development in early growth stages and
causes decay of storage roots in later growth stages. Sweetpotatoes grow best
in a sandy loam, well-drained soil. They have been produced at altitudes in
excess of 2000m and as far north as Canada.
Hundreds of cultivars and land races are used throughout the world and are
unique to countries or to smaller regions within countries. In industrialized
countries which grow sweetpotatoes, limited numbers of cultivars are grown. In
the United States, growers tend to grow only one or two major cultivars for
regional and national markets but may grow several cultivars in small amounts
for local markets. Despite the tremendous genetic variability available to
breeders in almost all traits of sweetpotato, the crop is considered to be
genetically vulnerable due to this heavy concentration in only one or two
cultivars. The two cultivars which account for most of the current US acreage
are 'Jewel' and 'Beauregard'.
In temperate climates sweetpotatoes cannot survive freezing temperatures and
storage roots must be stored overwinter and used as "seed" roots the next
spring. Overwintered storage roots are presprouted while still in storage by
raising the temperature to 20-30°C for 2-6 weeks. Roots are then placed in
ground beds in late winter, covered with up to 5cm of soil and covered with
plastic. Exact conditions and types of beds vary with location. Plastic is
removed after the threat of frost is over. Typically roots will produce enough
sprouts to begin planting in 5-6 weeks. Sprouts approximately 25cm in length
are either pulled from the mother roots or cut (cutting prevents spread of some
diseases but is costly in terms of labor) and planted in field rows using
mechanical 4 or 8 row transplanters. Optimum plant density depends on cultivar
but is usually around 40,000 plants/ha. Rows may vary from 1m to 1.25m apart;
in row spacing is usually 25-30cm.
Fertilizer is usually incorporated in the soil with an additional application
approximately 6 weeks after planting. Requirements depend on soil testing but
are normally in the range of 60kgN/ha and 120kgK/ha. Phosphorous is also
required but is only added in phosphorous deficient soils. Boron is usually
added to prevent a surface defect known as blister. Requirements for water
vary with soil type but can be generally estimated as 18-20mm/week early in the
season, 40-45mm/week during the middle part of the season when storage roots
are enlarging rapidly, and a reduction to about 20mm late in the season.
Excessive moisture early in the season delays storage root development and
enlargement; late in the season, it induces cracking and/or rotting of roots.
Herbicides are normally necessary for sweetpotato production but
recommendations vary in different states. Few herbicides are labeled for use
with sweetpotato. Nematicides may also be necessary. The severity of
nematode damage varies from state to state and thus all released cultivars may
not have nematode resistance. As with herbicides, choices for nematicides are
Storage roots are harvested when the production of the Number 1 grade (5-9cm in
diameter) is maximized. This depends on cultivar but is usually between 90-120
days. Harvest is usually done mechanically with a number of different types of
harvesting aids. Typically vines are cut off and roots are thrown to the soil
surface using tractors with various types of dish plows; the roots are picked
up by hand and transferred to bulk bins in trucks. Mechanical harvesters which
lift the roots onto a belt and into bulk bins are available but are slow and
expensive. Roots harvested early are usually washed, graded and sent directly
to market because of high prices. Subsequently harvested roots are placed in
buildings to cure (30-35°C, 90%RH) and then are stored (10-15°C;
85-90%RH) until needed for market. Curing promotes wound healing and provides
a barrier to prevent bacteria and fungi from entering wounds received during
harvest and handling. Properly cured roots will store for 12 months or longer
with 15-25% losses under the best conditions. Temperature must not drop below
12°C in order to prevent physiological cold damage to which sweetpotatoes are
particularly susceptible. Relative humidity should remain between 80 and 90%
to prevent dehydration as the living storage roots continue to respire. As
they are needed for marketing, roots are removed from storage rooms, processed
through a mechanical washer/grader and packed into boxes of about 15kg. Wash
water may contain chlorine or other approved fungicides to reduce infection of
wounds generated by the grading procedure.
Roots which are designated as the next year's "seed" roots are usually
harvested late and are kept separate from the commercial stock. Most states
have some form of voluntary certified seed program to assure quality of stock
used for propagation.
Most of the sweetpotatoes which are processed in the US are canned. Because
the best prices are received for roots on the fresh market, those going to
canning processors are the smaller roots (2.5-5cm in diameter). Roots larger
than those desired for fresh market (>9cm in diameter) are usually sent to
baby food processors.
US Germplasm Repository, Plant Introduction Station, Griffin, GA (Curator R. L.
World Collection: International Potato Center, Lima, Peru (Curator Z. Huaman)
Contact North Carolina Crop Improvement Association, 3709 Hillsborough St.,
Raleigh, NC 27607 Tel: 919 515 2851 FAX: 919 515 7981
Wanda W. Collins, Department of Horticultural Science, Box 7609, North Carolina
University, Raleigh, North Carolina 27695-7609 Tel: 919 515 1205; FAX: 919 515
2505; e-mail: Wanda_Collins@ncsu.edu
- Edmond, J. B. and G. R. Ammerman. 1971. Sweet Potatoes: Production,
Processing, Marketing. The AVI Publishing Co., Inc., Westport, CT, 334p.
- International Potato Center, 1987. Exploration, maintenance and utilization of
sweet potato genetic resources. Report of the First Sweet Potato Planning
Conference. Lima, Peru. 369 p.
- Woolfe, Jennifer A. 1992. Sweet Potato: An Untapped Food Resource. Cambridge
University Press, Cambridge, UK. 643 p.
- Bouwkamp, John C. 1985. Sweet Potato Products: A Natural Resource for the
Tropics. CRC Press, Inc., Boca Raton, FL.271 p.
- Asian Vegetable Research and Development Center. 1982. Sweet Potato:
Proceedings of the First International Symposium. AVRDC Press, Shanhua,
Tainan, Taiwan, ROC. 481 p.
- Yen, D. E. 1974. The Sweet Potato and Oceania: An Essay in Ethnobotany.
Bishop Museum Press, Honolulu, HI. 389p.
Jonathan Schultheis, Department of Horticultural Science, Box 7609, North
Carolina State University, Raleigh, North Carolina 27695-7609 Tel: 919 515
1225; FAX: 919 515 2505; e-mail: Jonathan_Schultheis@ncsu.edu
J. M. Cannon, Resident Director, Sweetpotato Research Station, Louisiana State
University Agricultural Center, Chase, LA 71324. Tel: 318 435 2155
[Contributor: Wanda W. Collins, Department of Horticultural Science, North
Carolina State University]
Copyright © 1995. All Rights Reserved. Quotation from this document should cite and acknowledge the contributor.
Last update Tuesday, February 24, 1998 by aw