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.

Sorghum breeders have not made much yield improvement in new sorghum varieties in Kenya since Serena in was released in the late 1960s. KARI Mtama-1 which was released in 1993 has no yield advantage over Serena. A yield plateau for sorghum in Kenya is apparent. A new breeding approach was adopted to break that yield barrier. Development of hybrid sorghum was proposed and is expected to break the yield barrier and also deliver cultivars that meet farmers' main requirements. The objectives of the study were to (1) identify farmers' requirements in sorghum cultivars, constraints to sorghum production and why improved cultivars from research are not being adopted, (2) characterize male and female parents and establish if genetic distance could identify superior parent populations for hybrid production (3) estimate genetic variance components and determine the possibility of using GCA and SCA estimates in choosing parents for use in hybrid production, (4) test hybrids and open pollinated variety (OPV) parental lines for stress tolerance and identify tolerant hybrids for further testing and, (5) compare single cross hybrids and OPV varieties in yield performance. Participatory rural appraisal in Kitengei and Nzambani areas of Kambu showed that sorghum was especially important in semi-arid parts of Kenya. Food, trade, feed, nursing food and thatching were the most important uses of sorghum. High grain and stover yield, large grain size, early maturity, drought tolerance, pest and disease resistance, coloured grain and intermediate plant height were the major requirements of farmers. Fifty-three pollinators and forty-one male sterile parents were introduced from four sources and screened together with 27 pollen parents from Kenya. Parents and hybrids were tested in 4 environments: high and low plant density, in high and low moisture regimes laid out in a triple square lattice design in Kenya, with parents having two additional tests in South Africa. Males, females, sexes and parental sources differed significantly in head weight. There were sex x country and sex x environment interactions for head weight. Genetically distant parents' populations had higher chances of superior heterosis. Parents showed significant additive genetic variance in head weight. The regression of non-additive to additive genetic variance was roughly one and significant. Three female and five male parents were suitable for production of hybrids adapted to multiple environments. Hybrids and OPV lines significantly varied in head weight. Hybrids were superior to OPV lines in most agronomic traits. Economic superiority of the hybrids was sufficient to cover cost of hybrid production and distribution in Kenya. Hybrids and OPV lines varied significantly for plant density stress. Hybrids were less sensitive to stress and more productive than OPV lines under population density stress. KARI varieties were sensitive to plant density stress. In general low sensitivity to stress was beneficial and hybrids had superior yield to inbred varieties. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Sorghum is the fifth most important cereal crop in the world and ranks third in Africa, and it is potentially the number one cereal for the semi-arid environments in sub-Saharan Africa. Sorghum varieties have been developed specifically for grain, fodder or stem sugar but not for dual-purpose combining grain and stem sugar. Such varieties could be beneficial to the resource-poor farmers by providing grain for food and sugar rich stalks that can be sold for bioethanol production. However, there are no suitable dual-purpose cultivars on the market. There is also limited information about the combining ability, gene action and genetic effects and relationships between stem sugar and grain yield which is required in devising appropriate strategies for developing dual-purpose sorghum varieties. Furthermore, there is also lack of information about the perceptions of resource-poor, small-scale farmers and other important stakeholders on the potential of dual-purpose sorghum production and the value chain. Therefore, the objectives of this study were to: (i) investigate the awareness of the farmers, industry and other stakeholders on the dual-purpose sorghum varietal development and its feasibility, (ii) screen germplasm for use as source materials useful for grain yield and stem sugar traits, (iii) investigate the inheritance and heterosis levels attainable in grain yield components and stem sugar traits in dual-purpose sorghums, (iv) determine the relationships between stem sugar traits and grain yield components in dual-purpose sorghums, and (v) investigate the fertility restoration capacities of selected male-fertile lines used as male parents through the evaluating seed set in experimental dual-purpose hybrids. Two surveys were conducted to establish stakeholders’ level of awareness and perceptions on the potential and feasibility of developing and utilising dual-purpose sorghums in Southern Africa. One survey was carried out in the semi-arid tropical lowlands in Zimbabwe under the conditions of small-scale and resource-poor farmers while the other, which targeted sugar industries, plant breeders, engineers, political leaders, economists and extension workers, was conducted in South Africa and Zimbabwe. Data were analysed using SPSS computer package. Results showed that both farmers and the non-farmer stakeholders were in agreement on the view that dual-purpose sorghum would be a viable enterprise that could alleviate poverty, enhance food security, create rural employment and boost rural development in southern African countries. Farmers were willing to adopt the cultivars if they were made available. The stakeholders also suggested mechanisms to overcome the infrastructural, economic and technical challenges associated with the technology. Screening of regional and international germplasm collection held at the University of KwaZulu- Natal in South Africa revealed high genetic variability for grain yield, stem brix and stem biomass yield that can be exploited in dual-purpose sorghum cultivar development. Ten lines were selected for inclusion as parents in the dual-purpose sorghum breeding programme. The selections were crossed to eight cytoplasmic male-sterile lines originating from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in accordance with a North Carolina Design II mating scheme. The 18 parents, together with the 80 experimental hybrids generated and two check varieties were evaluated for grain yield and stem sugar traits in six tropical low- and mid-altitude environments in Mozambique, South Africa and Zimbabwe. Stem sugar concentration and stem biomass were measured at the hard dough stage of each entry due to maturity differences between the genotypes. Grain yield was measured and adjusted to 12.5% moisture content. Data were analysed in GenStat computer package following a fixed effects model. Both additive and non-additive gene effects were important in controlling stem brix, stem biomass, grain yield and the associated traits in dual-purpose sorghum. This showed that breeding progress can be achieved through hybridisation and selection. Cultivars showing high stability, and high standard and better-parent heterosis for the three traits were identified implying that breeding for general adaptation was an option and that productivity could be enhanced by breeding hybrid cultivars. The relationships between traits were estimated using correlation and path-coefficients analysis. Grain yield was found to be negatively and significantly associated with stem brix but was positively and significantly associated with stem biomass. This implied that breeding for high stem brix might compromise grain yield but selection for high stem biomass improved grain yield. Stem biomass and stem brix were not significantly correlated. The general negative relationship between grain and stem brix was attributed to the predominance of entries with contrasting performances for the two traits. However, the relationship between grain yield and stem brix of the top 20 performing entries showed a non-significant relationship between stem brix and grain yield suggesting that the traits were independent of each other. This finding was confirmed by the presence of crosses that combined high performance for both stem brix and grain yield as well as stem biomass among the hybrids. The relationships between stem brix and stem biomass for the top 20 performers remained non-significant while that between stem biomass and grain yield became stronger, positive and significant. Direct selection for stem brix and grain yield was shown to be more important than indirect selection, while selection for stem biomass improves grain yield but had no effect on stem brix. Therefore, it is possible to breed dualpurpose sorghum cultivars and the identification of genotypes combining the desirable traits is prudent in addition to general relationships information. The study on fertility restoration capacities as evaluated through hybrid seed set showed that fertility restoration was under the control of genes with both additive and non-additive action. Since restoration is conferred by a single dominant gene (Rf1), this could have arisen from the action of the modifier genes that have been previously reported to influence it. This showed that fertility restoration can be improved through breeding. Hybrid combinations showing complete seed set and high performance for grain, stem brix and stem biomass were identified and are potential dual-purpose sorghum cultivars. Overall, the study showed that development of dualpurpose sorghum cultivars would be feasible and genotypes identified as potential cultivars in this study will be forwarded for further testing across many sites and seasons in the target environments. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.