Micropropagation of Sweet Potato (Ipomoea batatas L.)
Sweet potato (Ipomoea batatas (L.) Lam.) ranks seventh among crops grown for food, and tenth among all crops grown worldwide (FAO 1986). Besides food production, sweet potato has good potential as a biomass crop for ethanol and methane (Smith and Frank 19
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Introduction Sweet potato (Ipomoea batatas (L.) Lam.) ranks seventh among crops grown for food, and tenth among all crops grown worldwide (F AO 1986). Besides food production, sweet potato has good potential as a biomass crop for ethanol and methane (Smith and Frank 1984). The accumulated carbohydrate in the roots can be efficiently digested and converted into ethanol or methane gas and used for energy (Smith et al. 1987). Sweet potato is a member of the Convolvulaceae (morning glory) family and is usually grown for its edible roots. It is often confused with yam since both storage organs look and taste similar. Yams, however, belong to the genus Dioscorea (family Dioscoreaceae) and are monocots, diploid (2n = 20), and their storage organs are tubers, whereas sweet potatoes are dicots, hexaploid (2n = 90), and the storage organs are botanically classified as roots (Wilson and Collins 1988). The literature often confuses the issue by incorrectly calling the sweet potato's storage organ a tuber (Kays 1985). Sweet potato originated in tropical America (Henderson et al. 1984). Since then it has been distributed worldwide. Sweet potatoes require a growing season that has at least 4 to 5 frost-free months to produce ample-sized storage roots. Warm conditions are required since temperatures at or below 15 oc result in little or no plant growth (Pierce 1987). Above 15 oc, Harter and Whitney (1927) determined plant growth rates continued to increase up to a temperature of 35 °C, while Pierce (1987) reported optimum growth occurred at air temperatures of 29 oc. The crop grows best in well-aerated, sandy-type soils, with a pH ranging between 5 and 7.8 (O'Hair 1984). However, good yields of 17.9 and 17.0 MT/ha have been obtained at soil pH values of 4.3 and 4.6 (Abruna et al. 1978). Soil aeration, when limiting, can inhibit storage root formation and development (Wilson 1970).
2 Need for Micropropagation Commercial plantings of sweet potatoes are primarily for food production, but attention in recent years has focused on this crop as a biomass crop for energy Florida Agricultural Experiment Station Journal Series No. N-00418 1 Vegetable Crops Department, University of Florida, Gainesville, FL 32611, USA
Biotechnology in Agriculture and Forestry, Vol. 19 High-Tech and Micropropagation III (ed. by Y.P.S. Bajaj) © Springer-Verlag Berlin Heidelberg 1992
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R. P. Chee et al.
production. Southern Japan, in some instances, has used sweet potato for energy production (Yen 1974). Mass production, however, is limited by the high cost of vegetative propagation (Cantliffe et al. 1987). Problems with this planting method include the following: (1) length of time needed for plants to survive stressful conditions, (2) maintenance and production of disease-free plants, (3) spatial requirements for large-scale production, and (4) labor costs to maintain the plant propagules (Cantliffe et al. 1987). Sweet potato plants generally do not produce seeds since most cultivars are selfincompatible (Hernandez and Miller 1964; Wang 1964; Onwueme
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