ORIGIN AND STRUCTURE OF ADVENTITIOUS ROOTS IN SWEET POTATO

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GENERAL INTRODUCTION

Sweet potato (Ipomoea batatas (L.) Lam.) belongs to the family Convolvulaceae. It is a herbaceous dicot widely grown throughout the tropics and warm temperate regions of the world between latitudes 40oN and S of the equator and between sea level and 2300 m altitude (Shukla, 1976; Hahn, 1977a; Bourke, 1982; Jana, 1982). Globally sweet potato is the seventh most important food crop after wheat, rice, maize, potato, barley, and cassava. Sweet potato is the second most important root and tuber crop in the world after potato (Horton, 1988). In Sub- Saharan Africa sweet potato is the third most important tuber crop after cassava (Manihot esculenta) and yam (Dioscorea spp.) (Ewell & Mutuura, 1994). More than 140 million tons of sweet potato is produced globally per year (FAO, 2000). The world average storage root yield of sweet potato has been estimated to be 14.8t ha-1 (FAO, 2000). Asia is the world’s largest sweet potato producing continent, with 129 million tons annual production. China with 121 million tons accounts for 86% of world sweet potato production. Nearly half of the sweet potato produced in Asia is used for animal feed, the remaining primarily used for human consumption, either fresh or as processed products.
Although African farmers produce only about 9 million tons of sweet potato annually, most of the crop is cultivated for human consumption. African yields are quite low at 4 to 5 tons per hectare, about a third of the Asian yields, indicating huge potential for future growth. In Africa the crop is grown on small scale, primarily to help ensure food security of the rural households (Ewell & Mutuura, 1994).
Sweet potato is cultivated in Ethiopia mostly for human consumption and as animal feed. It ranks third after Enset (Ensete ventricosum (Welw.) Cheesman,) and potato (Solanum tuberosum L.) as the most important root crop produced in the country. Sweet potato is mainly grown by small scale, resource poor farmers. According to FAO (2000) the Ethiopian national average storage root yield of sweet potato is 8t ha-1. Experimental storage root yields rangin between 30 and 73t ha-1 have been reported by Hossain et al., (1987), Siddique et al., (1988), Hall & Harmon, (1989), Bhagsari & Ashley, (1990) and Varma et al., (1994).

CHAPTER 1 GENERAL INTRODUCTION
1.1 References
CHAPTER 2 LITERATURE REVIEW
2.1 Crop uses
2.2 Crop Description
2.3 Environmental conditions
2.4 Production aspects
2.5 Planting material
2.6 Planting, weeding and fertilization
2.7Cropping systems
2.8 Growth analysis
2.9 Diseases and pests
2.10 Harvesting, curing and storage
2.11 References
CHAPTER 3 ORIGIN AND STRUCTURE OF ADVENTITIOUS ROOTS IN SWEET POTATO
3.1 Abstract
3.2 Introduction
3.3 Materials and methods
3.4 Result and discussion
3.5 Conclusion
3.6 References
CHAPTER 4 EFFECT OF TEMPERATURE AND SOIL MOISTURE CONTENT ON CUTTING ESTABLISHMEN
4.1 Abstract
4.2 Introduction
4.3 Materials and methods
4.4 Results
4.5 Discussion and conclusion
4.6 References
CHAPTER 5 INFLUENCE OF CUTTING CHARACTERISTICS O STORAGE ROOT FORMATION AT INDIVIDUAL NODES
5.1 Abstract
5.2 Introduction
5.3 Materials and methods
5.4 Results
5.5 Discussion and conclusion
5.6 References
CHAPTER 6 EFFECT OF CUTTING CHARACTERISTICS ON YIELD AND YIELD COMPONENTS
6.1 Abstract
6.2 Introduction
6.3 Materials and methods
6.4 Results and discussion
6.5 Conclusion
6.6 References
CHAPTER 7 PRODUCTION AND PARTITIONING OF DRY MATTER IN THREE SWEET POTATO CULTIVARS
CHAPTER 8 EFFECT OF PLANTING DENSITY AND CULTIVAR ON YIELD AND YIELD COMPONENTS
CHAPTER 9 SUMMARY
APPENDIX