Towards increasing and sustaining production of yam for food security and improved livelihoods in Uganda.
Yam (Dioscorea spp.) plays an important role in food security and is increasingly gaining importance as a source of income for smaller holder farmers in Uganda. However, the crop has not been given due attention in the national research and development (R&D) agenda in Uganda and nearly falls in the class of ‘neglected or orphaned crop’. The objective of this paper is to generate insights into the importance of yam in Uganda in order to increase production and improve food security. Primary and secondary information from studies conducted in Uganda show that the most popular yam types are the yellow varieties. Challenges include limited availability of yam, seed rendering it very expensive, high cost of staking materials and limited knowledge in yam agronomy and utilisation.
Yams: Dioscorea spp.
Publisher Summary Yams belong to the family Dioscoreaceae with about 650 species. The most important genus is Dioscorea comprising about 600 species. Of these, only seven are principal food sources for human diet in the tropics. These are D. rotundata Poir., D. cayenensis Lam., and D. dumetorum (Knuth) Pax in West and Central Africa, D. trifida L. in tropical America and the Caribbean islands, D. alata L. and D. esculenta (Lour.) Burkill in southeast Asia, and D. bulbifera L., which has a wide distribution though it is rarely intensely cultivated. The first two species alone account for most of the global annual output of yams, and D. alata and D. esculenta are next in importance. Some medicinal yam species are also economically important as the sources of sapogenin such as D. floribunda Mart. & Gal., D. spiculiflora Hemsl., and D. composita Hemsl. Their production is not common among the major yam-producing countries. This chapter provides an overview of the cytology, phylogeny, and genetics. The chapter also discusses the objectives of yam breeding, strategies and methods for yam breeding, selection of these methods, and application of biotechnology in yam breeding. Use of biotechnology for the genetic improvement of yams is in its embryonic stage. Most of the progress reported on the application of biotechnology to yams has been in the area of tissue culture. The genetic improvement of yams for food and other uses is a well-known activity in crop research but will continue to offer promise only if the potentials are exploited by sustained research.
Investigations on the rôle of organic matter in plant nutrition
1. As the result of decomposition of green manure in a swamp soil, the coarse fractions (including coarse and fine sand) of the surface layer (first 3 inches) decreased by 11·2 per cent. while the fine ones (silt+clay) increased by 9·8 per cent. in the course of 43 days. The effect was less pronounced in the manured soil maintained at 60 per cent. saturation, while no alteration was to be noticed in the case of the unmanured specimens. 2. Treatment with dilute hydrochloric acid prior to dispersion had no appreciable effect on the estimates of mechanical composition obtained in the different cases. Loss in solution was also comparatively small. 3. The silica-sesquioxide ratio increased slightly as the result of decomposition of green manure in swamp soil. The composition of the fine fractions was also altered, the total percentages of the oxides of iron, aluminium and silicon increasing from 90·5 to 99·3 in the course of 71 days. 4. The practical significance of the above and related observations has been discussed.