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close this bookTraditional Storage of Yams and Cassave and its Improvement (GTZ)
View the document(introduction...)
View the documentPreface
View the document1 Introduction
View the document2 Socio-cultural aspects involved in the production of roots and tubers
View the document3 Basic comments on the storage properties of roots and tubers
close this folder4 Yams
View the document(introduction...)
View the document4.1 The environmental requirements of yams
View the document4.2 The yam tuber
View the document4.3 Farm-economic aspects of yam production
View the document4.4 Yam harvesting
close this folder4.5 Causes of storage losses for yams
View the document(introduction...)
View the document4.5.1 Dormancy
View the document4.5.2 Transpiration
View the document4.5.3 Respiration
View the document4.5.4 Germination
View the document4.5.5 Rot due to mould and bacteriosis
View the document4.5.6 Nematodes
View the document4.5.7 Insects
View the document4.5.8 Mammals
close this folder4.6 Traditional storage systems for fresh yams
View the document(introduction...)
View the document4.6.1 Leaving the yam tubers in the ridges after maturity
View the document4.6.2 Storing the yam tubers in trench silos
View the document4.6.3 Storage of yam tubers in heaps on the ground
View the document4.6.4 Storage of yam tubers in clamp silos
View the document4.6.5 Storage of yam tubers under a conical protective roof made of maize or millet stalks
View the document4.6.6 storage of yam tubers in mud huts
View the document4.6.7 The storage of yam tubers in the yam barn.
close this folder4.7 Measures to improve traditional yam storage
View the document(introduction...)
View the document4.7.1 Care in harvesting transport and storage
View the document4.7.2 Curing
View the document4.7.3 Influencing dormancy
View the document4.7.4 Influencing the storage climate
View the document4.7.5 control of rot
View the document4.7.6 Control of nematodes
View the document4.7.7 Control of insects damaging stored produce
View the document4.7.8 Measures for protection from mammals
View the document4.7.9 The improved traditional yam barn
close this folder5 Cassava
View the document(introduction...)
View the document5.1 The environmental requirements of cassava
View the document5.2 The cassava root
View the document5.3 Economic aspects of cassava production
View the document5.4 Causes of limitations to storage for fresh cassava roots
close this folder5.5 Ways of and limits to. storing fresh cassava roots
View the document(introduction...)
View the document5.5.1 Storing cassava roots in the soil after maturity
View the document5.5.2 Traditional methods of storing fresh cassava roots
View the document5.5.3 Storage of fresh cassava roots in clamp silos
View the document5.5.4 Storing fresh cassava roots in crates
View the document5.5.5 Storing fresh cassava roots in a dip
View the document5.5.6 Storing fresh cassava roots in plastic bags
View the document5.5.7 Use of modern methods to store fresh cassava roots
View the document5.5.8 Measures to prepare fresh cassava roots for storage
View the document5.5.9 Suitability of storage systems for fresh cassava roots on a small farmholder level
close this folder5.6 The processing of cassava roots
View the document5.6.1 The purpose of processing
View the document5.6.2 Hydrogen cyanide and its release
View the document5.6.3 The production of cassava chips
View the document6 Summary
View the document7 Bibliography

4.2 The yam tuber

Economically the most important part of the yam is its tuber This can vary greatly in shape and size and makes manual harvesting very difficult and has so far prevented any kind of mechanisation in harvesting. Cultivated forms of yam mostly produce cylindrical tubers which cam be very heterogeneous in size and weight.

The outer part of the tuber forms several layers of cork. These layers constitute effective protection from lesions, water loss and against the penetration of pathogens in the soil as well as in storage after the harvest The inner part of the tuber is formed by a tissue which is interwoven with vascular channels Carbohydrates, mainly in the form of starches, are stored in this tissue. Apart from the most important constituents of the tuber, water and carbohydrates, this also contains small quantities of proteins, fats and vitamins. As can be seen from Table 6, the tubers of various varieties of yam differ in the relative composition of their constituents.

Table 6: The composition of various species of yam tubers

Variety

Moisture

Carbohydrates

Fats

Crude protein

D. alata

65-73

22-29

0,1-0,3

1,1-2,8

D. rotundata

58 - 80

15 - 23

0,1 - 0,2

1,1 - 2,0

D. esculenta

67-81

17-25

0,1 -0,3

1,3- 1,9

D. bulbifera

63-67

27-33

0,1

1,1-1,5

NB. The figures have been rounded. The results for D. rotundata correspond to those for D. cayenensis which was not included in the table
Source: Coursey, 1967 (modified)

The yam tuber is primarily for vegetative propagation if complete tubers are used for propagation, germs will form in the region of the head. Also segments of the tuber can germinate as long as these include a piece of the outer surface of the tuber. The ability of the tuber to form germs at any point on its surface is made use of by the "Miniset Propagation Method" (INPT, 1988). Using this method, the plants required per hectare can be reduced from approximately two tons to approx. 400 kg