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Ipomoea batatas (L.) Lam.

Syn.: Ipomoea fastigiata Choisy
Convolvulaceae
Sweetpotato, Camote

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.

  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Toxicity
  5. Description
  6. Germplasm
  7. Distribution
  8. Ecology
  9. Cultivation
  10. Harvesting
  11. Yields and Economics
  12. Energy
  13. Biotic Factors
  14. References

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

Complete list of references for Duke, Handbook of Energy Crops
Last update Wednesday, January 7, 1998 by aw