|Traditional Storage of Yams and Cassave and its Improvement (GTZ)|
The economically most important part of the cassava plant is the tuber-like thick root. This develops from thin roots which take the nutrients out of the soil. Only a few roots per plant develop into tuberous, thick roots.
The thick root is connected to the plant by a short, wooden neck. It has a longish round form and can grow to between 15 and 100 cm and reach a weight of 0.5 to 2.0 kg.
The cassava root consists of three layers. The cork periderm and the cortex below this form the exterior protection for the root. Both cell layers are only a few millimetres thick. The central part of the root is a storage tissue where starch is kept. In the centre of the root there is a small vascular bundle running lengthwise. There are cells which can secrete latex in the storage tissue as well as in the cortex.
The thickening growth of the roots does not begin until the roots absorbing the nutrients have penetrated the soil to prepare the way. The arrangement of thick roots is influenced by how the cuttings are planted. If these are planted vertically, thick roots develop and lie close to each other like in a bundle. If the cuttings are planted horizontally, roots will form at each node. The thick roots then develop at some distance from each other at the nodes of the cuttings (ONWUEME, 1977).
The thick roots have no function in vegetative propagation which occurs through cuttings from the stalk. The reason why reserve substances accumulate in the thick roots has not been completely clarified. It can however be assumed that these reserves serve to help the plant survive unfavourable situations e.g., longer arid periods. This ultimately also defines the good resistance of cassava to dryness.
The thick root in a fresh condition contains approx. 62% water, 35% carbohydrates (mainly in the form of starch), 1 - 2% proteins, 0.3% fats, 1 - 2 % fibres and 1 % minerals (ONWUEME, 1977). In comparison to the yam tuber, the cassava root contains more energy but far less protein. An unbalanced diet containing only cassava can lead to deficiency. Deficiency and poisoning can also be caused by the high concentration of hydrogen cyanide especially when cassava is not processed or insufficiently processed before eating (.cf. Chapter 6.2).