Production Practices and Quality Assessment of Food Crops. Vol. 1

32 R. M. Madakadze and J. Kwaramba
intensified by the deficiency. Sufficient quantities of P increases the length of storage
roots.
4.4.7.3. Potassium
Sweet potatoes have a high demand for potassium (K + ), which is required for the
enlargement of storage roots. The shape and total soluble solids content of storage
roots are also affected by this mineral. Low K + reduces the number of roots formed
and those that are formed are long, spindly and malformed (Clark and Moyer,
1988; Pierce, 1987). The deficiency has also been associated with greater weight
loss and surface rot of roots in storage. Increasing the availability of K + tends to
cause an increase in the carotene content of storage roots. High concentrations of
K + can reduce the solids content of storage roots, which can lead to reduced dry
matter content and reduced firmness in canned products (Clark and Moyer, 1988).
4.4.7.4. Calcium
The effect of Ca deficiency on the ability to produce storage roots varies, depending
on the cultivar, from negligible effect to total failure to produce roots (Clark and
Moyer, 1988). Calcium deficiency causes soft, very small and misshapen tubers
to be formed.
4.4.7.5. Boron
Symptoms of B deficiency in storage roots are diagnostic – they are an internal
brown spot and blister. The blister caused by B deficiency is characterized by
small raised bumps on the root surfaces and plant stunting (Miller and Nielsen, 1970;
Peet, 2002; Pierce, 1987). Except for very susceptible cultivars, the blister does
not show up until sweet potatoes have been stored for several months. Internal brown
spots are similar in appearance to symptoms associated with internal X. They may
occur anywhere within the storage root but are most common near the vascular
ring. The spots are brown, vary in size, and have indefinite margins.
5. CONCLUSION
The quality of produce on the market is affected by several factors including preharvest
factors, stage of harvest, transportation, and environmental conditions in
storage. This chapter focused on preharvest factors only. The role of these factors
have been highlighted showing how quality can be affected. The focus on physiological
disorders is also important as it highlights some of the cultural control
methods that need to be taken care of in order to produce high quality produce
that can be stored for the maximum possible self life. This is not completely exhaustive
as t here are also other factors that can cause quality loss that cold not be
considered in this chapter.