- DISTRIBUTION AND PRODUCTION OF MAJOR ROOT VEGETABLES
- USE OF ROOT VEGETABLES IN THE UNITED STATES
- Cassava, Yams, and Aroids
- Potato
- Sweet potato
- POTENTIAL FOR INCREASED USE AND PRODUCTION OF SWEET POTATOES
- Ethnic Markets
- Development of New Value-added Products
- Sweet potato in Breads and Flours
- Use as Animal Feed or an Animal Feed Supplement
- POTENTIAL FOR NEW MINOR ROOT CROPS
- FUTURE PROSPECTS
- REFERENCES
- Table 1
Vegetables grown for their edible
roots or tubers encompass a wide range of starchy root crops, some of which are
true botanical roots and others which are tubers or corms. The most
economically significant root crops globally include potato (Solanum
tuberosum L.), sweet potato (also spelled sweet potato) [Ipomoea batatas
(L) Lam.], cassava (Manihot esculenta Crantz), yams (Dioscorea
spp.), and aroids [principally Colocasia esculenta (L.) Schott var. esculenta
and Xanthosoma spp.]. Although traditionally, root vegetables have been
considered low status and generally unimportant crops by consumers,
governmental organizations, and researchers, on a global scale they account for
three of the seven most important food crops in the world (FAO 1989).
Of these five majors root crops,
only potato and sweet potato are grown to any extent in the United States, and
of these two, sweet potato has the greatest potential for increased usage and
consumption. However, there are other starchy root vegetables grown in various
areas of the world where they are of local economic and cultural importance and
which could conceivably be considered potential new crops for domestic consumption
(O'Hair 1990a, b). Among the most promising may be some of the Andean root
crops (Sperling and King 1990). In addition, apios (Apios americana),
has received attention as a potential new crop. Apios is unique among the root
and tuber crops mentioned in that it fixes nitrogen and also produces edible
tubers, fleshy roots, and seeds (Putnam et al. 1991). Tubers are high in
protein and carbohydrates (Walter et al. 1986) and are preferred by some to the
domestic potato, Solanum tuberosum. The potential of apios as a new crop
has been described by Reynolds et al. (1990).
DISTRIBUTION
AND PRODUCTION OF MAJOR ROOT VEGETABLES
Most root vegetables are produced in
developing countries. In developed countries, 99% of root production is in
potato (Rhoades and Horton 1990). Fresh weight production of the five major
root vegetables (potato, sweet potato, cassava, yams, and aroids) is listed in Table 1 and compared with the other major crops
which are produced at a level of 100 million tonnes globally. Potatoes,
cassava, and sweet potato rank among the seven major, global food crops which
are produced at that level. Yams and aroids are produced at a much lower level,
but are important staple food crops on a regional level.
Sweet potatoes and potatoes are
produced in the United States (Table 1). Cassava, yams, and aroids are long
season crops requiring one to two years for maturity which precludes their
being grown in any significant amount in the continental United States.
Although some short-season types are available, they still require six months
or more for maturity. There are some experimental results indicating that yams
could be successfully produced domestically (Marsh 1991).
USE
OF ROOT VEGETABLES IN THE UNITED STATES
Cassava,
Yams, and Aroids
There is little consumption or
consumer familiarity with cassava, yams, or aroids in the United States outside
of ethnic populations. This status is not likely to change except for increased
consumption by steadily increasing ethnic populations. They are, however,
imported into the United States from the Caribbean and Latin America and are
available for consumption. Quality of imported products is generally poor
unless purchased immediately from a local market. Once the product reaches
grocery shelves, it is generally well below fresh quality standards.
Studies in Missouri have shown that
yams can be produced in that state by starting them in a greenhouse for six
weeks followed by about 22 weeks in the field (Marsh 1988). Yield per plant was
much lower than those obtained in tropical growing areas (3.5 kg/plant as
opposed to 20 to 30 kg/plant) but yams were of good marketable quality.
Potatoes have been the most widely
used root vegetable grown in the United States; current per capita consumption
is about 56.4 kg. Quality is excellent, consumption is high, and there are a
multitude of products available to the consumer. Potatoes are used in many ways
as a vegetable and as a snack food. Even so, new types of potatoes are being
introduced to the fresh market for consumers to try. Among these are yellow
potatoes and blue potatoes. The unique characteristics of these potatoes are
novelty traits which may capture a very small portion of present markets. They
do represent a potential for specialty markets at very high prices.
Sweet
potato
Sweet potatoes are consumed in the
United States on a much smaller scale than potatoes with the per capita
consumption now about 5.8 kg. Quality is excellent but few products are
available. Normally sweet potatoes can be purchased fresh, canned (whole or
cut), as a reconstituted patty, and in baby food. They are most often used in
pies or as a candied vegetable. Use is seasonal revolving around Thanksgiving,
Christmas, and Easter. This seasonality has been a major problem in marketing
efforts to increase consumption. In the past, various products have been
developed from sweet potatoes, such as chips and fries, but none have been
successful.
Sweet potato does have the potential
for increased production and consumption. Sweet potato germplasm, like that of
potato, is diverse with many types with different flesh colors, skin colors,
textural properties, and nutritional components. There is excellent potential
for the development of new products and new types of sweet potatoes to fit
various demands of different consumer groups. Breeding efforts in the United
States have focused almost exclusively on a single phenotype: a sweet vegetable
type (luxury type) which has copper skin, deep orange flesh (high carotene),
sweetness, and moist texture (Collins 1987). The American public, through
surveys, has expressed a flexibility of choice for some attributes, but the
desired marketing type has remained the same. Although this type can still be
greatly improved through breeding efforts, it is unlikely that the demand for
the luxury type of sweet potato will increase significantly unless new uses and
products are developed.
POTENTIAL
FOR INCREASED USE AND PRODUCTION OF SWEET POTATOES
Ethnic Markets
Populations of ethnic cultural
groups in the United States are substantial and continue to increase (Marsh
1991). Opportunities exist for American growers in the United States to produce
different types of sweet potatoes for those markets. Unlike cassava, aroids,
and yams, importation of sweet potatoes into the United States is prohibited by
law. Hence, there is little or no supply for potential ethnic markets because
the type of sweet potato demanded by those markets is different from the normal
phenotype which is now the major focus of domestic commercial sweet potato
production. Preferred types are red or white skinned, cream to white flesh,
non-sweet or very slightly sweet, and dry in texture. Consumers in these groups
are more accustomed to eating sweet potato as a carbohydrate energy source
(staple or supplemental staple type) than as a dessert or sweet vegetable
(luxury type).
Staple, supplemental staple, and
luxury types of sweet potatoes were described by Villareal (1981) and further
characterized by Collins (1987). Desired traits for each type are very
different and breeding programs must have specific programs for developing
acceptable cultivars of these types.
Some efforts do exist to meet the
demands of ethnic markets. In Florida, "boniatoes," white-fleshed,
dry, firm textured sweet potatoes, have been produced for many years for the
Hispanic market. Cultivars used in this production have been brought into
Florida from nearby Caribbean islands, such as Cuba (O'Hair et al. 1983), and
have not been improved for United States growing conditions. A new Japanese
clone recently entered the domestic market and is being grown in California and
North Carolina. This cultivar may not be ideally suited to domestic growing
conditions. There is ample opportunity for breeders to respond to the need for
new phenotypes to meet new market opportunities. No surveys have been conducted
to assess potential demand, but it could equal as much as 25% of current
production if the crop is properly marketed. Market feasibility studies would
establish the extent of the potential market, and should they be positive,
convince growers of the profitability of producing this type of sweet potato.
The North Carolina State University sweet
potato breeding program has a small project underway to develop the type of sweet
potato described. The variability in sweet potato is great enough so that
almost any type desired can be constructed with proper breeding procedures.
Several clones with different characteristics are in various stages of testing.
There are also several research projects underway to study specific
characteristics which are important in breeding clones with the necessary
traits, such as studies on the heritability and factors affecting ß-amylase
activity which lead to non-sweet types. Non-sweetness has proved to be one of
the most difficult traits to incorporate in these clones even though non-sweet
types exist in the breeding materials. Results of preliminary tests indicate
that sweetness and the perception of sweetness is very complex and that
lowering ß-amylase activity alone may not necessarily lead to non-sweet sweet potatoes.
Development
of New Value-added Products
The range of variability in sweet
potatoes is so great that many different phenotypes can be made available for
special product development depending on the characteristics needed. Often it
is difficult to determine, even through trial and error, what the best
characteristics are for particular products. Value-added products such as
french fries, chips, and flakes, have been developed from sweet potato but none
has been successfully marketed for any length of time. Much effort has been
devoted to sweet potato fries. However, consumer comments often refer to the
sweetness, texture, and oil content as problems. The products developed, such
as fries, have always been developed from the existing single phenotype grown
in the United States today and this may be a major reason for the disappointing
results with such products.
Sweet
potato in Breads and Flours
There have been efforts in the
private sector to capitalize on the enormous potential for sweet potato
products. At least one patent has been granted for producing sweet potato bread
and flour composed of 100% sweet potato. These products are marketed as
hypoallergenic for people who cannot tolerate grain breads and flours. The
price is quite high (approximately $12/lb. for flour and up to $17 for a loaf
of bread) as is demand. The inventor in this case has surmounted the problems
normally associated with increased amounts of sweet potato flour in breads. A
"boniato" type sweet potato from Florida is used to make these products.
As the process is patented, it is not available for general production at
present. Several other patents are pending for other processes involving sweet
potato (K. Slimak pers. commun.).
Where wheat has to be imported or
can be grown only with extensive inputs (such as in developing countries), sweet
potato is a viable alternative component for breads and flours. There are
disadvantages such as reduced loaf volume and decreased storage life (Keya and
Hadziye 1990), but the reduced costs and decreased dependability on imports may
outweigh the disadvantages. The acceptability of component breads and flours is
excellent with as much as 10 to 15% content of sweet potato flour (Sammy 1984).
Some researchers have reported using up to 25% sweet potato flour with no
adverse consumer reaction. In the United States, where wheat is plentiful and
relatively inexpensive, this alternative use of sweet potato does not appear to
be economically justified except as a specialty product.
Use
as Animal Feed or an Animal Feed Supplement
Sweet potato is used as an animal
feed and supplement in developing countries (Gohl 1981). Both vines and roots
are used. Starch and protein digestibility of raw sweet potatoes has been cited
as an obstacle to increased use for animal feed. Trypsin inhibitor has been
implicated in poor protein digestibility. Genetic variability does exist for
level of trypsin inhibitor activity and genotypes with no measurable activity
are available. In the United States, competition with maize (Zea mays
L.) is a major impediment to increased usage of sweet potato for animal feeds
and supplements although interest is growing in the potential use as a
component in chicken feed.
POTENTIAL
FOR NEW MINOR ROOT CROPS
Recently, much attention has been
focused on minor crops which are very important to the culture and subsistence
of local farmers in many parts of the world. Concern has been raised about the
future security of the genetic resources of these minor crops. In particular,
recent attention has been focused on the Andean root and tuber crops. In
addition to potatoes, several roots and tubers have played a significant role
in the Andean culture and are cultivated in that area. Two of these which are
more well known than others could be domestically grown. A third is lesser
known but could also have some potential for production.
Oca (Oxalis tuberosa Molina,
Oxalidaceae) is probably the most well known root vegetable other than potato
in the Andean region. It is quite unusual in appearance with a brightly colored
edible tuber and a pleasant mild flavor. Oxalic acid is a component of the
tubers, but levels are generally not higher than those found in some other
popular crops (S. O'Hair pers. commun.). Oca is commercially produced in Peru
and has been commer-cialized in New Zealand (Yamaguchi 1983). A number of
clones are grown and many accessions have been collected (S. O'Hair pers.
commun.).
A second Andean root vegetable,
ulluco or olluco or ullucu(s) (Ullucus tuberosus Caldas, Bassellaceae)
is also grown commercially in the Andean regions of Peru. This is also a crop
of wide genetic diversity with perhaps 50 to 70 clones being grown in the
Andean region (S. O'Hair pers. commun.). External colors of tubers can be white,
yellow, green, or magenta; the plants are frost resistant and require 140 to
150 days for tuber development (Yamaguchi 1983).
Mashua or anu (Tropaeolum
tuberosum Ruiz & Pav. Family Tropaeolaceae) is a third Andean root
vegetable and is related to the ornamental nasturtium. It is not commercially
produced on the same scale as the other two crops. Consequently, it is not as
well known as the other two. It is said to have medicinal properties and some
cultivars may have pesticide properties (S. O'Hair pers. commun.).
Each of the three Andean root
vegetables can be eaten fresh or dehydrated. All are used in the Andean region,
along with potato, to make chuo, a dehydrated and frozen product which can last
several years and serves as a secure food source when necessary. Each has the
potential to be grown in certain areas of temperate climates.
FUTURE PROSPECTS
There are several opportunities for
increased production and usage of root and tuber crops in the United States. Of
the five major root crops, sweet potato has the greatest potential for new uses
and increased production. As sweet potatoes cannot be imported in the United
States, there is no significant current supply for specific types of sweet
potatoes suited to ethnic cultural preferences. Growers in North Carolina, who
produce over 30% of the sweet potatoes in the United States, have been
reluctant to begin production of new types for ethnic markets. Market
feasibility studies need to be undertaken to determine the potential markets.
With respect to new and unknown root
crops, three Andean root crops, oca, ulluco, and mashua, offer potential for
new production. However, a lack of funds to investigate the possibilities may
preclude any development.
REFERENCES
- Collins, W.W. 1987. Improvement of nutritional and edible qualities of sweet potato for human consumption, p. 221-226. In: Exploration, maintenance and utilization of sweet potato genetic resources: Report of the first sweet potato planning conference, International Potato Center, Lima, Peru.
- FAO. 1990. 1989 production yearbook. Rome, Italy.
- Gohl, B. 1981. Tropical feeds. FAO, Rome, Italy.
- Keya, E.L. and D. Hadziyev. 1990. p. 188-196. In: R.H. Howeler (ed.). Proc. 8th Symposium of the International Society for Tropical Root Crops. Oct. 30-Nov. 5, 1988. Bangkok, Thailand, 1990.
- Marsh, D.B. 1988. Production of specialty crops for ethnic markets in the United States. HortScience 23:628.
- Marsh, D.B. 1991. Ethnic crop production: An overview and implications for Missouri. HortScience 26:1133-1135.
- O'Hair, S.K. 1990a. Tropical root and tuber crops. Hort. Rev. 12:157-196.
- O'Hair, S.K. 1990b. Tropical root and tuber crops, p. 424-428. In: J. Janick and J.E. Simon (eds.). Advances in new crops. Timber Press, Portland, OR.
- O'Hair, S.K., R. McSorley, J.L. Parrado, and R.F. Matthews. 1983. The production and qualities of Cuban sweet potato cultivars in Florida. Proc. Amer. Soc. Hort. Sci. Tropical Region 27:35-41.
- Reynolds, B.D., W.J. Blackmon, E. Wickremesinhe, M.H. Wells, and R.J. Constantin. 1990. Domestication of Apios americana, p. 436-442. In: J. Janick and J.E. Simon (eds.). Advances in new crops. Timber Press, Portland, OR.
- Rhoades, R. and D. Horton. 1990. p. 8-19. In: R.H. Howeler (ed.). Proc. 8th Symposium of the International Society for Tropical Root Crops. Oct. 30-Nov. 5, 1988. Bangkok, Thailand.
- Sammy, G.S. 1984. The processing potential or tropical root crops. Proc. Caribbean Regional Workshop on Tropical Root Crops, Jamaica, April 10-16, 1983. p. 199.
- Sperling, C.R. and S.R. King. 1990. Andean tuber crops: worldwide potential, p. 428-435. In. J. Janick and J.E. Simon (eds.). Advances in new crops. Timber Press, Portland, OR.
- Villareal, R.L. 1981. Sweet potato. Proc. First International Symposium. Asian Vegetable Research and Development Center, Tainan, Taiwan. p. 3-16.
- Walter, W.M., E.M. Croom, G.L. Catignani, and W.C. Thresher. 1986. Compositional study of Apios princena tubers. J. Agr. Food Chem. 34:39-41.
- Yamaguchi, M. 1983. World vegetables: Principles, production and nutritive values. AVI, Westport, CT.
Table
1. Production
of major world food crops and root cropsz.
Crop
|
Global
production (000 tons) |
United States
production (000 tons) |
Wheat
|
538,056
|
55,407
|
Rice
|
506,291
|
7,007
|
Maize
|
470,318
|
191,197
|
Barley
|
168,964
|
8,784
|
Potato
|
276,740
|
16,659
|
Sweet potato
|
133,234
|
542
|
Cassava
|
147,500
|
---
|
Yam
|
23,459
|
---
|
Aroids
|
5,814
|
3
|
Root crops total
|
590,176
|
17,204
|
zSource: FAO 1989 Production Yearbook (FAO 1990)