Climate change, shrinking arable land, burgeoning population and malnutrition have made all
aspects of crop improvement a critical issue. Of these, nutritional quality of crops is perhaps
one of the most important aspects. Most cereals consumed in marginal agro-ecological zones
of Africa, for example sorghum and maize are impoverished nutritionally. Given therefore
the sole reliance on and the levels of consumption per day of such staples (up to 450 g/day), it
is clear that most people cannot obtain the recommended daily allowance (RDA) for many
nutrients including fibre, edible oil, protein, vitamins and mineral elements. In this thesis, the
development of a sorghum mutant population using gamma irradiation and the subsequent
employment of various analytical techniques to unravel multiple mutant traits with a
significant positive impact on nutritional enhancement in sorghum is described. Protein
analysis revealed a mutant designated SY accumulating (at the time) the highest ever reported
amount of free lysine (21.6 g/100g) and other essential amino acids and that these changes
were associated with induced protein polymorphisms. Adaptation of proton induced x-ray
emission (PIXE) for the spatial profiling of the distribution of 9 elements in sorghum seed
tissue allowed for the discovery of mutants with variations in the concentrations and
distribution of these elements. The observed changes included enhanced or diminished
accumulation of elements in preferential accumulation tissues and entire changes in cellular
localisation. The locations within a cell and the quantities of an element are often critical
determinants of bioavailability. The accumulation of multiple mutations affecting multiple
nutritional traits in individual mutant sorghum clearly indicates the versatility of gamma
irradiation induced mutations in addressing multiple nutritional challenges of sorghum. This
desirable phenomenon was further demonstrated by electron microscopic analysis of starch
granules and protein bodies across the mutants. Scanning electron microscopy (SEM) and
transmission electron microscopy (TEM) revealed changes in size, shape, ultra-structure and
packed cell volumes of seed protein- and starch bodies. Induced mutation had a major effect on the protein body structure which in turn resulted in changes to protein digestibility. High
digestibility mutants had a unique dense protein matrix with dark inclusions. However,
improved protein quality traits were also associated with floury endosperm texture. Since
endosperm texture is an important grain quality attribute and plays a major agronomic role, it
is important to ensure that future work focuses on improving grain hardness. The mutants
obtained in this study are therefore a valuable germplasm source for sorghum breeding and
present real opportunities for addressing nutritional challenges of sorghum. / Ph.D. University of KwaZulu-Natal, Durban 2013.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/11247 |
| Date | January 2013 |
| Creators | Mbambo, Zodwa. |
| Contributors | Lin, Johnson., Mehlo, Luke. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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