From the Handbook
of Energy Crops, unpublished
by James A. Duke
Ipomoea
batatas (L.) Lam.
Syn.: Ipomoea fastigiata
Choisy
Convolvulaceae
Sweetpotato, Camote
Uses
Cultivated
mainly for the tuber, used as vegetable, eaten
boiled, baked fried, or dried and ground into flour to make biscuits,
bread, and other pastries. Tubers also dehydrated in chips, canned,
cooked and frozen, creamed and used as pie fillings, much like pumpkin.
Leafy tops eaten as vegetable and sold in markets in Malaysia. Greatly
esteemed as feed for farm animals; with 3 kg green sweet potatoes
equivalent to 1 kg of corn, with a food value rated 95–100% that of
corn. Dry vines have feed value which compares favorably with alfalfa
hay as forage (Reed, 1976).
Folk Medicine
According to Hartwell
(1967–1971), the leaf decoction is used in folk remedies for tumors of
the mouth and throat. Reported to be alterative, aphrodisiac,
astringent, bactericide, demulcent, fungicide, laxative, and tonic,
sweetpotato is a folk remedy for asthma, bugbites, burns, catarrh,
ciguatera, convalescence, diarrhea, dyslactea, fever, nausea, renosis,
splenosis, stomach distress, tumors, and whitlows (Duke and Wain, 1981).
Chemistry
Per
100 g, the root is reported to contain 108–121 calories, 68.5– 72.3 g
H2O, 1.0–1.7 g protein, 0.2–0.4 g fat, 25.6–31.0 g total carbohydrate,
0.7–1.0 g fiber, 0.7–1.0 g ash, 21–36 mg Ca, 38–56 mg, P, 0.7–2.0 mg
Fe, 10–36 mg Na, 210–304 mg K, 35–5,280 mg b-carotene equivalent,
0.09–0.14 mg thiamine, 0.04–0.06 mg riboflavin, 0.6–0.7 mg niacin, and
21–37 mg ascorbic acid. The usual range of values for different
constituents is: moisture, 58–75; protein, 0.5–3.5; fat, 0.2–1.5;
N-free extract, 18.0–37.0; sugars, 2.2–5.6; fiber, 0.6–2.5; and ash,
0.6–1.5%. Indian types with white flesh contain little or no carotene,
while American types with pink flesh contain as high as 5.4–7.2 mg/100g
of caroten. Vitamins present in the tubers are: thiamine, 0.09–0.14;
riboflavin, 0.05–0.10; and vitamin C, 16–22 mg/100 g. Sucrose and a few
reducing sugars are present, but maltose, mannose, galactose, and
pentose occur, if at all, only in traces. The essential amino acids
present in the total proteins are as follows (calculated to 16.0 g N):
arginine, 1.9; histidine, 1.4; lysine, 4.3; tryptoplian, 1.8;
phenylalanine, 4.3; methionine, 1.7; threonine, 3.8; leucine, 4.8;
isoleucine, 3.6; and valine, 5.6 g. The pectic substances (total, 0.78;
soluble, 0.43%) present in fresh tubers contain: uronic acid, 60; and
methoxyl, 4–5%. Other constituents in the tubers: phytin (1.05%), two
mono-amino-phosphatides (probably lecithin and cephalin), organic acids
(oxalic acid, 0.1%), phytosterolin, phytosterol, resins, tannins, and
coloring matter. Sweetpotato contains calcium, 30; magnesium, 24;
potassium, 373; sodium, 13; phosphorus, 49; chlorine, 85; sulphur, 26;
and iron, 0.8 mg/100 g; iodine, 4.5 mg/kg; magnanese, copper, and zinc
are present in traces. The spent pulp, or pomace, left after the
extraction of starch, gave the following values: dry matter, 90.2;
protein, 2.5; fat, 0.3; fiber, 9.6; N-free extract, 71.8; mineral
matter, 6.0; digestible protein, 0.4; and total digestible nutrients,
69.0%; and nutritive ratio, 171.5. Analysis of the dried vines gave:
dry matter, 90.7; protein, 12.6; fat, 3.3; fiber, 19.1; NFE, 45.5;
mineral matter, 10.2; digestible protein, 8.9; and total digestible
nutrients, 51.7% (C.S.I.R., 1948–1976). Of more than a dozen African
vegetables, this was the richest in folate (1.93–1.96 mg/g) (Hug et al,
1983).
Toxicity
Roots may contain the laxative ipomoein.
Description
Tuberous-rooted
perennial, usually grown as an annual; top herbaceous, drying back to
ground each year; stems forming a running vine up to 4 m long, usually
prostrate and slender, with milky juice, lateral stem-branches arising
from the short stem and usually not branched; leaves ovate-cordate,
borne on long petioles, palmately veined, angular or lobed, depending
on variety, green or purplish; flowers rare, especially in United
States, like common morningglory, white or pale violet, axillary,
funnel-shaped, borne singly or in cymes on short peduncles; pods round;
seeds 1–4 per pod, flattened, hard-coated, angular. Fl. summer; fr.
late summer and fall (Reed, 1976).
Germplasm
Reported
from the Indonesia-Indochina and Middle and South American Centers of
Diversity, sweetpotato, or cvs thereof, is reported to tolerate
bacteria, disease, drought, fungus, hydrogen flouride, high pH,
laterite, low pH, mycobacteria, nematodes, peat, savanna, virus, and
weeds (Duke, 1978). Of the more than forty cvs that have been grown in
the US, about 10 are of commercial value now. These fall into two
categories: food types and feed types. They are further divided into
dry or firm types and moist or soft types. The present outstanding
soft-fleshed cvs are 'Porto Rico', 'Nancy Hall', 'Triumph', and
'Australian Canner'; firm-fleshed types are 'Big-stem Jersey', 'Yellow
Jersey', 'Maryland Golden', and 'Orlis' (Jersey orange). The best,
high-yielding white-fleshed, high-starch feed cv is 'Pelican
Processor', which is somewhat resistant to stem rot, and is especially
adapted to the lower South. Also 'Whitestar' is a white-fleshed cv,
high-yielding, high-starch variety, better adapted to the middle and
northerly sweetpotato areas than 'Pelican Processor'. Both contain less
carotene than the yellow food types (Reed, 1976).
Distribution
Native
to the American Tropics. Introduced and cultivated in many tropical and
subtropical countries, there becoming important food crop, especially
in India, China, Philippine Islands, and the South Seas Islands (Reed,
1976).
Ecology
Ranging
from Cool Temperate Steppe to Wet through Tropical Thorn to Wet Forest
Life Zones, sweetpotato is reported to tolerate annual precipitation of
3.1 to 42.9 dm (mean of 153 cases = 15.0), annual temperature of 8.4 to
28.5°C (mean of 152 cases = 23.5), and pH of 4.3 to 8.7 (mean of 88
cases = 6.4). Well-adapted to tropical and subtropical climates,
sweetpotato will grow successfully over a wide range of climatic
conditions where the average frost-free growing season is at least 5
months. Freedom of frost is not enough. Days and nights must be fairly
warm. Will grow north to Maryland, New Jersey, New York, Iowa, and
Kansas, where it is grown as an annual. Most of the crop is grown in
areas receiving 10 dm or more rainfall annually, but will grow in areas
receiving less than 8.5 dm if irrigated. Rainfall should be well
distributed over the growing season (0.25 cm or more per week) until 2
or 3 weeks before harvest and then about half that. Sweetpotatoes are
fairly drought-tolerant and can survive some rather long dry spells
during the summer after growth is well along. They resume growth with
adequate rains, but should not be considered a dry-weather crop. Low
water supply impairs crop quality. Soils rated good for sweetpotatoes
include moderately deep, very friable fine sandy loams, sandy loams, or
loamy fine sands. Soils must be well-drained. Subsoils of clay are
satisfactory unless they are tight and sticky. Some friable,
well-drained loams and silt loams are highly productive. Excellent
soils have surface layers more than 30 cm in depth, those from 15–30 cm
are considered good. Slopes should be gentle, with little tendency to
become eroded. If soils are too deep, tubers grow too deep for
harvesting machines.
Cultivation
In
tropical areas, sweetpotatoes flower and cross-pollinate easily.
Hwever, as plants do not come true from seed, seeds are rarely used for
propagation purposes. In more northern areas where plants never flower,
all propagation is by vegetative means, from transplants produced by
bedding mother roots, or from rooted cuttings. Sweetpotatoes are grown
over a wide range on farms of various types: truck farms, dairy farms,
cotton farms, tobacco farms, corn-and-hog farms, and others. Crops that
should be grown on any one field during the years between Sweetpotato
plantings on that field will depend on what other crops are most
profitably grown on that farm. Sweetpotato can follow successfully any
one of a wide variety of crops or be grown on new land. Sweetpotatoes
should be transplanted only after the soil has warmed up well, in late
spring. It is undesirable to grow sweet potatoes on soils too rich in
manures. Plants obtained from bedded mother roots and cuttings taken
from early vine growth are planted about 10 days after frost-free date.
Early transplanting is best. Soil fertility and freedom from diseases
must be maintained. Usually both form new roots so readily that it is
unnecessary to treat them with hormones. Best cuttings consist of ca 20
cm of the ends of sturdy vines. They may be taken from open-field plant
beds or from early transplants that have produced vines. Most
sweetpotato plants are obtained from slips or plants of seed stock
grown in various ways in seedbeds. Plants are spaced about 30 cm apart
in rows about 1.1 m apart (ca 31,250 plants/ha), or in rows 1.3 m apart
(ca 26,350 plants/ha), or in rows 1.6 m apart (ca 21,250 plants/ha).
Sweetpotatoes are transplanted by hand or machine. On large fields,
machine planting is more economical and gives more uniform stands.
Three men with a 1-row planter can set 3,500 to 4,000 plants per hour,
with one man driving and 2 setting. With a 2-row planter, 5 men can set
7,000 to 8,000 plants per hour. If the soil is moist enough for setting
without water, more can be set per hour. High yields of high quality
sweetpotatoes can be obtained only on soils of high fertility, good
drainage, and suitable texture. Plants respond well to good soil
management and fertilizer practices. The most profitable yields have
been generally obtained with 1.5–2.25 MT of fertilizer mixtures
containing 2–4% nitrogen, 8% phosphoric acid, and 8–10% potash. On
fields where good amounts of green manures or animal manures have been
turned under, often no more than 2% of nitrogen is needed. On lighter
sandier soils, 10% of potash is recommended. Fertilizer generally
should be applied in two stages, one just before the ridges are
prepared ca 2 weeks before planting, when 0.75 MT/ha is thoroughly
mixed in the soil where the ridge is to be, with the ridge thrown up so
that most of tile fertilizer lies deep in the ridge, and the remainder
applied as top-dressing to the sides of the ridge 2 or 3 weeks after
transplanting. Sweetpotatoes do best on soils that are slightly to
moderately acid. On very acid soils that are deficient in calcium,
applications of ground limestone have markedly increased in yields. It
is undesirable to apply so much lime that the soil is neutralized.
Sometimes sweetpotatoes are grown in the West with irrigation. The time
and amount of water applied vary according to the soil and climate. In
general, on furrow-irrigated lands, six to eight irrigations are
applied between transplanting and harvesting. In all cultivations, weed
control must be pratically perfect before the vines become long enough
to interfere with cultivation. Sweetpotatoes are poor competitors with
weeds. Weeds reduce yields and interfere with harvesting.
Harvesting
Sweetpotato
tubers have delicate skins that are very easily broken. The flesh also
is easily bruised, broken, or cut. Wounds are followed by decay unless
they are promptly healed before infection occurs. Roots should not be
allowed to become chilled either before or after being harvested.
Sweetpotatoes develop a substantial amount of the total yield in the
last 4–5 weeks before frost. Since large yields are necessary, the
storage crop is usually allowed to grow as late as possible without
storage quality being damaged by frost. For large yields 130 to 150
days growth is required. A crop for immediate marketing can be
harvested at any time that the roots are large enough for sale and that
a large enough crop has developed to be profitable. Early harvested
crops are lower in carotene content and in total solids. Probably the
best time to harvest for storage is after the leaves show slight
yellowing. The earliest planted fields should be harvested first. Large
plows with 14-inch or larger shares do less damage to the sweet
potatoes than smaller ones. They should be set deep enough to get under
the tubers and not cut them. A 16- to 18-inch tractor-drawn turning
plow with a vine-cutting colter in front of it is probably the best
tool for harvesting. Harvesting machines have been developed that dig
the sweetpotatoes, carry them onto a conveyor where dirt is shaken off
and returned to the ground, the roots moving onto a platform where they
may be sorted. Such a machine can harvest 600–800 22.5 kg crates a day.
The crates are taken to packing and storage houses for immediate
washing, regrading and repacking, or for curing, storage and later
repacking. Harvesting for seed stock is done at final harvest time.
Precautions must be taken to select seed stock from production hills,
from stock free from diseases, and from stock true to variety. Because
the crop has the disadvantage of storing poorly, sometimes it is sliced
and dried in the sun, or packed in sand or straw. With the development
of early and late races, planting for a succession of crop seems best
to shorten periods for storage. A processing plant in the production
area can prepare products for human food (canned and dehydrated), for
stock feed, and for industrial uses, of much material that would
otherwise be wasted (Reed, 1976).
Yields and
Economics
Average
yields vary from 17.5 to 27.5 MT/ha, depending on the cv and growing
conditions (Reed, 1976). In 1979, Texas about 4,400 ha worth more than
$5 million. In that year, the US produced 80,000 ha out of a world
total of 16 million ha (Patterson, 1979). In 1979, the world low
production yield was 400 in Mauritania, the international production
yield was 8,355, and the world high production yield was 80,000 kg/ha
in Israel. Other yield figures include 15 MT/ha in Argentina, 15–40 in
Japan, 40 MT in New England, 20 MT in Sri Lanka, and 22 MT in Taiwan.
Sweetpotatoes have long been considered the second most important
vegetable crop in the US, second only to white or Irish potatoes. Spain
is major producer in Europe; India grows sweetpotato in all states and
it ranks third in importance among tuber crops, exceeded only by potato
and cassava. In China, where it was introduced in 1594, sweetpotato is
often used more than rice and has been used to relieve famines. Per
capita consumption in China is about 28 kg/year; in Japan, 60 kg/year;
and in US, 8.5 kg/year. Production in the United States is about 1
million tons per year.
Energy
In
India, tops can add up to 10–32 MT/ha to 77 MT in 3 or 4 cuttings per
year. The sweet potato is regarded as a valuable raw material for
producing alcohol (also tactic acid, acetone, butanol, vinegar, and
yeast). A hectare of sweet potato can feed more people than a hectare
of cereal grains, with less energy input. "The green weight yield per
acre of sweetpotato vines is greater than the yield of green corn for
silage" ca 15–50 tons per hectare (Patterson, 1979). Indonesia is
planning 2000 gasohol plants, with the fuel coming from sweetpotato,
cassava, and sugar cane (AVRDC Centerpoint, winter 1981/1982).
Biotic Factors
Sweetpotato
is subject to injury from a number of diseases that may attack the
young plants in the hot bed or the growing crop in the field or may
cause decay in storage. The worst of these are stem-rot, black-rot,
foot-rot, soft-rot or ring-rot,and in the Southwest, root-rot. These
are described and illustrated, and control measures are given in
Farmers' Bulletin No. 1059, Sweet Potato Diseases. The sweetpotato is
not seriously injured by many insects but the sweetpotato root weevil
has been very injurious in sections of the South, especially in the
Gulf States. This insect threatens to become a serious menace to
sweetpotato growing. Cutworms frequently destroy the young plants by
cutting them off soon after they are set in the field (Williams, 1970).
Agriculture Handbook No. 165 (1960) lists the following as affecting
this species: Albugo
ipomoeae-panduratae (white rust), Alternaria sp.
(secondary leaf spot), Aspergillus
spp. (secondary storage rot), Botrytis
cinerea
(gray-mold rot), Cercospora
sp. (leaf spot), Choanephora
cucurbitarum
(leaf mold), Coleosporium
ipomoeae
(rust), Diaporthe
batatas
(dry rot of roots, stem rot), Elsinoe
batatas
(spot anthracnose), Endoconidiophora
fimbriata
(black rot of roots and stems), Epicoccum
sp. (storage rot), Erwinia
carotovora
(bacterial soft rot), Fuligo
violacea,
Fusarium
oxysporum
(surface rot of roots in storage), F.
oxysporum.f. batatas (stem rot), Helicobasidium purpureum (root
rot), Hypomyces
ipomoeae,
Macrophomina
phaseoli (charcoal rot of stored roots, stem rot), Meliola clavulata and M. malacotricha
(black mildew), Monilochaetes
infuscans, Mucor racemosus (storage rot), Penicillium sp.
(bluemold rot), Pestalotia
batatae (on roots), Phyllosticta
batatas
(leaf blight), Phymatotrichum
omnivorum
(root rot), Physarum
cinereum,
P. plumbeum,
Phytophthora sp. (root rot), Plenodomus destruens
(foot rot of stems and roots), Pyrenophora
terrestris (pink rot), Pythium spp.
(rootlet rot, mottle necrosis of mature roots, leak and ring rot in
transit and storage), Rhizoctonia
solani
(sprout rot, rootlet rot, stem canker), Rhizopus spp. (soft
rot, ring rot of stored roots), Schizophyllum
commune (dry rot of roots), Sclerotinia sp.
(storage rot following chilling), S.
minor (sprout rot in seedbeds), Sclerotium rolfsii (southern
blight, cottony rot), Septoria
bataticola (leaf spot), Streptomyces ipomoea
(soil rot), Trichoderma
spp. (punky rot of stored roots), Verticillum
albo-altrum
(wilt) (Ag. Handbook 165, 1960). Several viruses are known to infect
sweetpotatoes: A virus, B virus, Feathery mottle (sweetpotato internal
cork virus), Mottle and Mosaic, Tobacco mosaic, Vein-clearing, and
Mizugusare disease. Internal brown spot is due to boron deficiency.
Because sweetpotatoes are a tuber crop, many nematodes have been
reported on the crop, including the following species: Aphelenchoides
besseyii, Aphelenchus avenae, Belonolaimus gracilis, B. longicaudatus,
Criconemella onoensis, Ditylenchus destructor, D. dipsaci,
Helicotylenchus multicinctus, H. cavenessi, H. concavus, H.
microcephalus, H. pseudorobustus, Hemicriconemoides cocophillus,
Meloidogyne hapla, M. incognita, M. incognita acrita, M. javanica,
Nothotylenchus affinis, Pratylenchus brachyurus, P. coffeae, P.
pratensis, P. penetrans, P. scribneri, P. thornei, P. zeae,
Quinisulicius capitatus, Radopholus similis, Rotylenchulus reniformis,
Scutellonema brachyurum, S. clathricaudatum, Tylenchorhynchus
annulatus. T. claytoni, and Xiphinema americanum.
Insects attacking sweetpotato plants include the following species:
Long-horn beetles (Cerambicid),
Sweetpotato flea beetle (Chaetosnema
confinis),
Wireworms (Conoderus
amplicollis, C. falli, C. vespertinus), Sweetpotato weevil
(Cylas formicarius
elegantulus), Cucumber beetles (Diabrotica balteata
and D. undecim-punctata),
American plum borer (Euzophera
semifuneralis), Wireworm (Melanotus communis),
Tortoise beetles (Metriona
sp.), Flower beelte (Notoxus
calcaratus), Variegated-cutworm beetles (Systena blanda, S. elongata, S.
frontalis), Sweetpotato leaf-beetle (Typophorus nigritus viridicyaneus).
Methods for control should be obtained from local agricultural agents
(Reed, 1976).
References
Agriculture Handbook 165. 1960. Index of plant diseases in the United
States. USGPO. Washington.
Duke,
J.A. 1978. The quest for tolerant germplasm. p. 1–61. In: ASA Special
Symposium 32, Crop tolerance to suboptimal land conditions. Am. Soc.
Agron. Madison, WI.
Duke, J.A. and Wain, K.K. 1981. Medicinal plants of the world. Computer
index with more than 85,000 entries. 3 vols.
Hartwell, J.L. 1967–1971. Plants used against cancer. A survey. Lloydia
30–34.
Hug,
R.S., Abalaka, J.A., and Stafford, W.L. 1983. Folate content of various
Nigerian foods. J. Sci. Food & Agr. 34(4):404–406.
Patterson, D.R. 1979. True roots—sweet potatoes. Texas Ag.
Progress/Winter, 1979:8.
Reed, C.F. 1976. Information summaries on 1000 economic plants.
Typescripts submitted to the USDA.
Williams, L. 1970. Sweet potato (Ipomoea batatas L.). Typescript.
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