Cassava roots, when left attached to the main stem, can remain in the ground for several months without becoming inedible; farmers do often leave cassava plants in the field as a security against drought, famine or other unforeseen food shortage. It is from this property that cassava has earned its name as a famine reserve crop. However, once the roots have been harvested, they start deteriorating within 2 to 3 days, and rapidly become of little value for consumption or industrial applications. Two types of deterioration are known to occur. The first to appear therefrom named primary deterioration consists of physiological changes characterised by an internal root discoloration called vascular streaking or vascular discoloration Averre, 1967. It is displayed as blueblack or brownish occlusions and chemical deposits. The time to onset of primary deterioration and the rate at which it progresses, the intensity, pattern and distribution of the discoloration varies between cultivars and roots of the same plant. Some varieties deteriorate so fast they become inedible 24 hours after harvest Booth, 1976 while others have been reported to stand for 7 to 11 days at room temperature without any sign of discoloration Montaldo, 1973. From a biochemical point of view, primary deterioration of cassava roots is associated with a conversion of some of the starch to sugars Booth et al 1976, an accumulation of cyanogenic glucosides, a decrease in linamarase activity Kojima et al. 1983, and the onset of a number of enzymatic reactions leading to the accumulation of coloured compounds Wheatley and Schwabe, 1985. There is a strong association between the onset of primary deterioration and the occurrence of various forms of mechanical damage. Due to the nature of harvesting and handling operations, mechanical damage is unavoidable; cutting the root off the plant creates a wound; digging utensils may cut or scrap the roots. Breaking off of the root tips and bruising do occur during transportation and handling. Wounds and bruises are the triggers of primary deterioration. Booth 1976 found that primary deterioration was essentially a wound response being initiated near the region of mechanical damage; unlike in other storage organs e.g. sweet potato, the response is not localised at the surface, but spreads down the root. Wounds and bruises also constitute points of entry for microorganisms leading to the second stage of cassava root spoilage, known as secondary deterioration.

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