UTANGULIZI
The sweet potato (Ipomoea batatas) is a dicotyledonous plant that belongs to the morning glory family Convolvulaceae. Its large, starchy, sweet-tasting, tuberous roots are a root vegetable.[1][2] In some parts of the English-speaking world, sweet potatoes are locally known by other names, including “yam” and kumara.[3] The young leaves and shoots are sometimes eaten as greens. The sweet potato is only distantly related to the potato (Solanum tuberosum) and does not belong to the nightshade family Solanaceae, but that family is part of the same taxonomic order as sweet potatoes, the Solanales.
The plant is a herbaceous perennial vine, bearing alternate heart-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered, with a smooth skin whose color ranges between yellow, orange, red, brown, purple, and beige. Its flesh ranges from beige through white, red, pink, violet, yellow, orange, and purple. Sweet potato varieties with white or pale yellow flesh are less sweet and moist than those with red, pink or orange flesh.[4]
Ipomoea batatas is native to the tropical regions in the Americas.[5][6] Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance—some others are used locally (e.g. I. aquatica “kangkong”), but many are poisonous. The genus Ipomoea that contains the sweet potato also includes several garden flowers called morning glories, though that term is not usually extended to Ipomoea batatas. Some cultivars of Ipomoea batatas are grown as ornamental plants under the name tuberous morning glory, used in a horticultural context.
Sweet potatoes with different skin colors
Naming
Origin, distribution and diversityEdit
The origin and domestication of sweet potato is thought to be in either Central America or South America.[10] In Central America, sweet potatoes were domesticated at least 5,000 years ago.[11] In South America, Peruvian sweet potato remnants dating as far back as 8000 BC have been found.
One author postulated that the origin of I. batatas was between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela.[12] The ‘cultigen’ had most likely been spread by local people to the Caribbean and South America by 2500 BC.[13] Strong supporting evidence was provided that the geographical zone postulated by Austin is the primary center of diversity.[12] The much lower molecular diversity found in Peru–Ecuador suggests this region should be considered as a secondary center of sweet potato diversity.
The sweet potato was grown in Polynesia before western exploration. Sweet potato has been radiocarbon-dated in the Cook Islands to 1000 AD, and current thinking is that it was brought to central Polynesia around 700 AD, possibly by Polynesians who had traveled to South America and back, and spread across Polynesia to Hawaii and New Zealand from there.[14][15] It is possible, however, that South Americans brought it to the Pacific, although this is unlikely as it was the Polynesians who had a strong maritime tradition and not the Native South Americans. The theory that the plant could spread by floating seeds across the ocean is not supported by evidence. Another point is that the sweet potato in Polynesia is the cultivated Ipomoea batatas, which is generally spread by vine cuttings and not by seeds.[16]
Sweet potatoes are cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth.[17] Due to a major crop failure, sweet potatoes were introduced to Fujian province of China in about 1594 from Luzon. The growing of sweet potatoes was encouraged by the Governor Chin Hsüeh-tseng (Jin Xuezeng).[18][19] Sweet potatoes were introduced as a food crop in Japan, and by 1735 was planted in Shogun Tokugawa Yoshimune’s private garden.[20] It was also introduced to Korea in 1764.[21]
Sweet potatoes became popular very early in the islands of the Pacific Ocean, spreading from Polynesia to Japan and the Philippines. One reason[original research?] is that they were a reliable crop in cases of crop failure of other staple foods because of typhoon flooding. They are featured in many favorite dishes in Japan, Taiwan, the Philippines, and other island nations. Indonesia, Vietnam, India, and some other Asian countries are also large sweet potato growers. Sweet potato, also known as kelang in Tulu is part of Udupi cuisine. Uganda (the second largest grower after China), Rwanda, and some other African countries also grow a large crop which is an important part of their peoples’ diets. The New World, the original home of the sweet potato, grows less than three percent (3%) of the world’s supply. Europe has only a very small sweet potato production, mainly in Portugal. In the Caribbean, a variety of the sweet potato called the boniato is popular. The flesh of the boniato is cream-colored, unlike the more popular orange hue seen in other varieties. Boniatos are not as sweet and moist as other sweet potatoes, but many people prefer their fluffier consistency and more delicate flavor.
Sweet potatoes have been an important part of the diet in the United States for most of its history, especially in the Southeast. From the middle of the 20th century, however, they have become less popular. The average per capita consumption of sweet potatoes in the United States is only about 1.5–2 kg (3.3–4.4 lb) per year, down from 13 kg (29 lb) in 1920. Southerner Kent Wrench writes: “The Sweet Potato became associated with hard times in the minds of our ancestors and when they became affluent enough to change their menu, the potato was served less often.”[22]
TransgenicityEdit
A study published in 2015 by scientists from Ghent University and the International Potato Center found that the genome of cultivated sweet potatoes contains sequences of DNA from Agrobacterium, with genes being actively expressed by the plants. The discovery of the transgenes was made while performing metagenomic analysis of the sweet potato genome for viral diseases. Transgenes were observed both in the sweet potato’s closely related wild relatives, and also were found in more distantly related wild species. This observation makes cultivated sweet potatoes the first known example of a naturally transgenic food crop.[23][24]
CultivationEdit
Producers (in million tonnes)[25]
Data for year 2011
China 81.7
Uganda 2.8
Nigeria 2.8
Indonesia 2.0
Tanzania 1.4
Vietnam 1.3
India 1.1
United States 1.0
World 106.5
Raw sweet potato
Nutritional value per 100 g (3.5 oz)
Energy
359 kJ (86 kcal)
Carbohydrates
20.1 g
Starch
12.7 g
Sugars
4.2 g
Dietary fiber
3 g
Fat
0.1 g
Protein
1.6 g
Vitamins
Vitamin A equiv.
beta-carotene
(89%)
709 μg
(79%)
8509 μg
Thiamine (B1)
(7%)
0.078 mg
Riboflavin (B2)
(5%)
0.061 mg
Niacin (B3)
(4%)
0.557 mg
Pantothenic acid (B5)
(16%)
0.8 mg
Vitamin B6
(16%)
0.209 mg
Folate (B9)
(3%)
11 μg
Vitamin C
(3%)
2.4 mg
Vitamin E
(2%)
0.26 mg
Minerals
Calcium
(3%)
30 mg
Iron
(5%)
0.61 mg
Magnesium
(7%)
25 mg
Manganese
(12%)
0.258 mg
Phosphorus
(7%)
47 mg
Potassium
(7%)
337 mg
Sodium
(4%)
55 mg
Zinc
(3%)
0.3 mg
Link to USDA Database entry
Units
μg = micrograms • mg = milligrams
IU = International units
Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database
Sweet potato, cooked, baked in skin, without salt
Nutritional value per 100 g (3.5 oz)
Energy
378 kJ (90 kcal)
Carbohydrates
20.7 g
Starch
7.05 g
Sugars
6.5 g
Dietary fiber
3.3 g
Fat
0.15 g
Protein
2.0 g
Vitamins
Vitamin A equiv.
(120%)
961 μg
Thiamine (B1)
(10%)
0.11 mg
Riboflavin (B2)
(9%)
0.11 mg
Niacin (B3)
(10%)
1.5 mg
Vitamin B6
(22%)
0.29 mg
Folate (B9)
(2%)
6 μg
Vitamin C
(24%)
19.6 mg
Vitamin E
(5%)
0.71 mg
Minerals
Calcium
(4%)
38 mg
Iron
(5%)
0.69 mg
Magnesium
(8%)
27 mg
Manganese
(24%)
0.5 mg
Phosphorus
(8%)
54 mg
Potassium
(10%)
475 mg
Sodium
(2%)
36 mg
Zinc
(3%)
0.32 mg
Link to USDA Database entry
Units
μg = micrograms • mg = milligrams
IU = International units
Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database
The plant does not tolerate frost. It grows best at an average temperature of 24 °C (75 °F), abundant sunshine and warm nights. Annual rainfalls of 750–1,000 mm (30–39 in) are considered most suitable, with a minimum of 500 mm (20 in) in the growing season. The crop is sensitive to drought at the tuber initiation stage 50–60 days after planting, and it is not tolerant to water-logging, as it may cause tuber rots and reduce growth of storage roots if aeration is poor.[26]
Soft, orange-fleshed variety of sweet potato
Depending on the cultivar and conditions, tuberous roots mature in two to nine months. With care, early-maturing cultivars can be grown as an annual summer crop in temperate areas, such as the northern United States. Sweet potatoes rarely flower when the daylight is longer than 11 hours, as is normal outside of the tropics. They are mostly propagated by stem or root cuttings or by adventitious roots called “slips” that grow out from the tuberous roots during storage. True seeds are used for breeding only.
They grow well in many farming conditions and have few natural enemies; pesticides are rarely needed. Sweet potatoes are grown on a variety of soils, but well-drained, light- and medium-textured soils with a pH range of 4.5-7.0 are more favorable for the plant.[2] They can be grown in poor soils with little fertilizer. However, sweet potatoes are very sensitive to aluminum toxicity and will die about six weeks after planting if lime is not applied at planting in this type of soil.[2] Because they are sown by vine cuttings rather than seeds, sweet potatoes are relatively easy to plant. Because the rapidly growing vines shade out weeds, little weeding is needed. A commonly used herbicide to rid the soil of any unwelcome plants that may interfere with growth is DCPA, also known as Dacthal. In the tropics, the crop can be maintained in the ground and harvested as needed for market or home consumption. In temperate regions, sweet potatoes are most often grown on larger farms and are harvested before first frosts.
In the Southeastern United States, sweet potatoes are traditionally cured to improve storage, flavor, and nutrition, and to allow wounds on the periderm of the harvested root to heal.[22] Proper curing requires drying the freshly dug roots on the ground for two to three hours, then storage at 29–32 °C (85–90 °F) with 90 to 95% relative humidity from five to fourteen days. Cured sweet potatoes can keep for thirteen months when stored at 13–15 °C (55–59 °F) with >90% relative humidity. Colder temperatures injure the roots.[27][28]
Main article: Sweet potato storage
YieldsEdit
In 2010, the world average annual yield for sweet potato crop was 13.2 tonnes per hectare. The most productive farms of sweet potato breeds were in Senegal, where the nationwide average annual yield was 33.3 tonnes per hectare.[29] Yields as high as 80 metric tonnes per hectare have been reported from farms of Israel.[30]
DiseasesEdit
Main article: List of sweet potato diseases
ProductionEdit
According to the Food and Agriculture Organization (FAO) statistics, world production in 2004 was 127 million tonnes.[31] The majority comes from China, with a production of 105 million tonnes from 49,000 km2 (19,000 sq mi). About half of the Chinese crop is used for livestock feed.[11]
Per capita production is greatest in countries where sweet potatoes are a staple of human consumption, led by Papua New Guinea at about 500 kg (1,100 lb)[32] per person per year, the Solomon Islands at 160 kg (350 lb), Burundi and Rwanda[33] at 130 kg (290 lb) and Uganda at 100 kg (220 lb).
About 20,000 tonnes of sweet potatoes are produced annually in New Zealand, where sweet potato is known by its Māori name, kūmara. It was a staple food for Māori before European contact.[34]
In the United States, North Carolina, the leading state in sweet potato production, provided 38.5% of the 2007 U.S. production of sweet potatoes. In 2007, California produced 23%, Louisiana 15.9%, and Mississippi 19% of the U.S. total.[35][36]
Mississippi has about 150 farmers growing sweet potatoes on about 8,200 acres (30 km2), contributing $19 million to the state’s economy. Mississippi’s top five sweet-potato-producing counties are Calhoun, Chickasaw, Pontotoc, Yalobusha, and Panola. The National Sweet Potato Festival is held annually the entire first week in November in Vardaman (Calhoun County), which proclaims itself as “The Sweet Potato Capital”.
Nutrient contentEdit
Besides simple starches, raw sweet potatoes are rich in complex carbohydrates, dietary fiber and beta-carotene (a provitamin A carotenoid), while having moderate contents of other micronutrients, including vitamin B5, vitamin B6 and manganese (table).[37] When cooked by baking, small variable changes in micronutrient density occur to include a higher content of vitamin C at 24% of the Daily Value per 100 g serving (right table).[38][39]
The Center for Science in the Public Interest ranked the nutritional value of sweet potatoes as highest among several other foods.[40]
Sweet potato varieties with dark orange flesh have more beta-carotene than those with light-colored flesh, and their increased cultivation is being encouraged in Africa where vitamin A deficiency is a serious health problem. A 2012 study of 10,000 households in Uganda found that children eating beta-carotene enriched sweet potatoes suffered less vitamin A deficiency than those not consuming as much beta-carotene.[41]
Comparison to other food staplesEdit
The table below presents the relative performance of sweet potato to other food staples. While sweet potato provides less edible energy and protein per unit weight than cereals, it has higher nutrient density than cereals.[3]
Nutrient content of major staple foods per 100g portion[42]
Nutrient component:
Maize / Corn[A]
Rice (white)[B]
Rice (brown)[I]
Wheat[C]
Potato[D]
Cassava[E]
Soybean (Green)[F]
Sweet potato[G]
Yam[Y]
Sorghum[H]
Plantain[Z]
RDA
Water (g) 10 12 10 13 79 60 68 77 70 9 65 3000
Energy (kJ) 1528 1528 1549 1369 322 670 615 360 494 1419 511 2000–2500
Protein (g) 9.4 7.1 7.9 12.6 2.0 1.4 13.0 1.6 1.5 11.3 1.3 50
Fat (g) 4.74 0.66 2.92 1.54 0.09 0.28 6.8 0.05 0.17 3.3 0.37
Carbohydrates (g) 74 80 77 71 17 38 11 20 28 75 32 130
Fiber (g) 7.3 1.3 3.5 12.2 2.2 1.8 4.2 3 4.1 6.3 2.3 30
Sugar (g) 0.64 0.12 0.85 0.41 0.78 1.7 0 4.18 0.5 0 15
Calcium (mg) 7 28 23 29 12 16 197 30 17 28 3 1000
Iron (mg) 2.71 0.8 1.47 3.19 0.78 0.27 3.55 0.61 0.54 4.4 0.6 8
Magnesium (mg) 127 25 143 126 23 21 65 25 21 0 37 400
Phosphorus (mg) 210 115 333 288 57 27 194 47 55 287 34 700
Potassium (mg) 287 115 223 363 421 271 620 337 816 350 499 4700
Sodium (mg) 35 5 7 2 6 14 15 55 9 6 4 1500
Zinc (mg) 2.21 1.09 2.02 2.65 0.29 0.34 0.99 0.3 0.24 0 0.14 11
Copper (mg) 0.31 0.22 0.43 0.11 0.10 0.13 0.15 0.18 – 0.08 0.9
Manganese (mg) 0.49 1.09 3.74 3.99 0.15 0.38 0.55 0.26 0.40 – – 2.3
Selenium (μg) 15.5 15.1 70.7 0.3 0.7 1.5 0.6 0.7 0 1.5 55
Vitamin C (mg) 0 0 0 0 19.7 20.6 29 2.4 17.1 0 18.4 90
Thiamin (B1)(mg) 0.39 0.07 0.40 0.30 0.08 0.09 0.44 0.08 0.11 0.24 0.05 1.2
Riboflavin (B2)(mg) 0.20 0.05 0.09 0.12 0.03 0.05 0.18 0.06 0.03 0.14 0.05 1.3
Niacin (B3) (mg) 3.63 1.6 5.09 5.46 1.05 0.85 1.65 0.56 0.55 2.93 0.69 16
Pantothenic acid (B5) (mg) 0.42 1.01 1.49 0.95 0.30 0.11 0.15 0.80 0.31 – 0.26 5
Vitamin B6 (mg) 0.62 0.16 0.51 0.3 0.30 0.09 0.07 0.21 0.29 – 0.30 1.3
Folate Total (B9) (μg) 19 8 20 38 16 27 165 11 23 0 22 400
Vitamin A (IU) 214 0 0 9 2 13 180 14187 138 0 1127 5000
Vitamin E, alpha-tocopherol (mg) 0.49 0.11 0.59 1.01 0.01 0.19 0 0.26 0.39 0 0.14 15
Vitamin K1 (μg) 0.3 0.1 1.9 1.9 1.9 1.9 0 1.8 2.6 0 0.7 120
Beta-carotene (μg) 97 0 5 1 8 0 8509 83 0 457 10500
Lutein+zeaxanthin (μg) 1355 0 220 8 0 0 0 0 0 30
Saturated fatty acids (g) 0.67 0.18 0.58 0.26 0.03 0.07 0.79 0.02 0.04 0.46 0.14
Monounsaturated fatty acids (g) 1.25 0.21 1.05 0.2 0.00 0.08 1.28 0.00 0.01 0.99 0.03
Polyunsaturated fatty acids (g) 2.16 0.18 1.04 0.63 0.04 0.05 3.20 0.01 0.08 1.37 0.07
A yellow corn B raw unenriched long-grain white rice
C hard red winter wheat D raw potato with flesh and skin
E raw cassava F raw green soybeans
G raw sweet potato H raw sorghum
Y raw yam Z raw plantains
I raw long-grain brown riceT
Utangulizi
Viazi vitamu ni moja kati ya mazao makuu ya mizizi nchini Tanzania ambalo hulimwa kwa ajili ya chakula. Zao hili ni moja kati ya mazao ya kinga ya njaa kutokana na sifa yake ya kuvumilia ukame. Zao la viazi vitamu, asilia yake ni Amerika ya Kati na ya Kusini. Nchini Tanzania, zao hili hulimwa zaidi katika mikoa ya Mwanza, Shinyanga, Dodoma, Morogoro,Kagera,Arusha na Ruvuma.
Matumizi
Viazi vitamu hutumika kama chakula kwa kutayarishwa katika njia mbalimbali kama vichembe, na Matobolwa. Pia Unga wa viazi vitamu hutumika kutengeneza vyakula kama keki, maandazi, kalimati, tambi na Juice. Majani ya viazi huliwa kama mboga pia hutumika katika kutayarisha mboji.
Aina
Kuna aina nyingi za viazi vitamu zinazolimwa ulimwenguni. Hapa nchini Tanzania aina zinazolimwa zaidi ni Ukerewe, Simama, Kakamega, Karoti C, Mwananjemu, Ali mtumwa mayai, Mavuno, Pananzala, Kibakuli, Sinia,Vumilia na Polista
Uzalishaji
•Zao hili hustawi maeneo mengi Nchini Tanzania. Viazi hustawi vizuri katika maeneo ya tambarare yenye udongo tifutifu, unaoruhusu maji kupenya kwa urahisi. Udongo wa mfinyazi na wenye kokoto nyingi haufai kwani huzuia mizizi kupenya na kupanuka.
•Shamba jipya litayarishwe vizuri kwa kufyeka vichaka na kung’oa visiki. Majani yafukiwe wakati wa kutengeneza matuta ili kuongeza rutuba ya udongo.
•Viazi vipandwe kwa kutumia Marando yenye urefu wa sentimita 30 kwa mavuno bora.
•Inashauriwa kutumia sehemu ya juu ya shina kwa mavuno zaidi. Marando yapandwe katika umbali wa sentimita 25 hadi 30 kutoka mmea hadi mmea na sentimita 60 hadi 75 kutoka tuta hadi tuta. Viazi pia vyaweza kupandwa kwa kutumia viazi vyenye afya vyenye uzito wa kati ya gramu 20 hadi 30. Hata hivyo inashauriwa kutumia marando ili kupata mavuno zaidi na kuepuka kuenea kwa magonjwa.
Kutunza shamba
•Ni muhimu kupalilia viazi vitamu katika miezi miwili ya mwanzo ili kuupa mmea nguvu ya kutambaa vizuri. Baada ya muda huo, viazi huweza kufunika ardhi na hivyo huzuia uotaji wa magugu.
•Viazi hushambuliwa na wadudu mbalimbali wakiwemo kipepeo, mbawa kavu, fukusi na minyoo fundo.Pia hushambuliwa na magonjwa yakiwemo magonjwa yanayotokana na virusi kama Sweet Potato Chlorotic Stunt virus (SPCSV). Magonjwa na wadudu yaweza kudhibitiwa kwa kuzingatia usafi wa shamba, kubadilisha mazao, na kuzingatia udhibiti sango.
Uvunaji
•Viazi vitamu huwa tayari kuvunwa miezi mitatu hadi minne tangu kupanda kutegemea hali ya hewa. Viazi vinaweza kuvunwa kidogo kidogo kwa kutumia mikono, vijiti, jembe, au rato kadri vinavyohitajika. Aidha inashauriwa viazi visiachwe ardhini muda mrefu bila kuvunwa kwani vitakomaa sana na kuwa na nyuzi, na hivyo kuharibu ubora wake. Pia kuacha viazi muda mrefu hukaribisha mashambulizi ya wadudu kama fukusi na kuoza. Kwa maeneo makubwa zaidi, inashauriwa kutumia mashine ya kukokotwa na ng’ombe. Uvunaji ufanywe kwa uangalifu ili kuhakikisha viazi visikatwekatwe wala kuchubuliwa wakati wa kuvuna.
•Mavuno ya viazi hutofautiana kulingana na aina, hali ya hewa, na udongo. Mavuno ya viazi yanakadiriwa kufikia tani 20 kwa hekta.
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