Sorghum [Sorghum bicolor (L.) Moench] is a major food security crop for millions of people in sub-Saharan Africa and the fourth most important crop in Africa. The potential sorghum yields are limited due to a number of abiotic, biotic and socio-economic constraints. Among the biotic stresses is the parasitic weed, Striga hermonthica, which inflicts yield losses ranging from 30-100%. Various control options have been recommended to reduce levels of Striga damage. However, these techniques need to be integrated for effective control and to boost sorghum productivity. A series of experiments was conducted to integrate host resistance improvement and the use of a biological control agent, Fusarium oxysporum f.sp. strigae to control Striga hermonthica. These studies were also focused on improving breeders‟ awareness of the traits that farmers‟ desire, on the assumption that farmers‟ variety preference traits are the missing link in technology development and adoption process for S. hermonthica management. The objectives of the study were to: 1) determine farmers‟ views on sorghum production opportunities; threats; indigenous knowledge and perceptions; breeding priorities; Striga infestation; and the coping mechanisms of farmers in the north eastern and north western Ethiopia, 2) evaluate sorghum genotypes for compatibility to F. oxysporum inoculation where grown in Striga infested soil in controlled environments, 3) determine field responses of sorghum genotypes and F. oxysporum compatibility for integrated Striga management (ISM), 4) determine the variability present among selected sorghum genotypes exhibiting S. hermonthica resistance, and compatibility with the biological control agent using phenotypic and simple sequence repeat (SSR) markers, 5) identify F. oxysporum compatible sorghum parents and hybrids with high combining ability for grain yield, yield components, and Striga resistance for ISM, and 6) undertake farmers‟ participatory assessment, and identify their preferred traits for sorghum genotypes under ISM, simultaneously with the breeders‟ evaluation. A participatory rural appraisal (PRA) research was conducted involving 315 farmers in nine districts of three administrative zones within two provinces in Ethiopia. Sorghum landraces were preferred by >85% of participants rather than previously improved released varieties. The participating farmers listed and prioritized their sorghum production constraints. In the North Shewa and North Wello zones drought was the most important constraint, followed by Striga. In the Metekel zone Striga was the number one constraint followed by a lack of genotypes with high grain quality. Controlled environment experiments were conducted involving greenhouse and laboratory tests in order to evaluate 50 sorghum genotypes for their compatibility with F. oxysporum and for possible deployment of the bio-control agent to control Striga. Striga population was reduced by 92% through the application of F. oxysporum, resulting in yield increment of 144%. Twelve sorghum genotypes were identified as promising parents for breeding and to control Striga through integration of host resistance and F. oxysporum seed treatment. During field and sick plot plot evaluations differential responses to F. oxysporum application among the sorghum genotypes were observed for various attributes including Striga plant height. Most traits showed highly significant (p<0.001) genotype X site interactions. Similarly, the main effects of F.oxysporum application were highly significant (p<0.001) across sites for most of the traits. The genotype and genotype X environment biplot identified 13 genotypes that consistently performed well following Fusarium application. The variability present among 14 selected sorghum genotypes exhibiting S. hermonthica resistance, and compatibility with a biological control agent, Fusarium oxysporum, were determined using phenotypic and 20 polymorphic simple sequence repeat (SSR) markers. Highly significant (p<0.001) differences were detected among genotypes for phenotypic traits. Principal component analysis showed three components that accounted for 73.99% of the total variability exhibited among genotypes. Cluster analysis allocated the genotypes into two major groups, one with a further two subgroups based on morphological traits, showing clear demarcations between the genotypes. The SSR markers revealed high levels of polymorphisms among genotypes, with the mean number of alleles per locus being 6.95 and the mean polymorphic information content being 0.80. The observed genetic diversity was relatively wide, with the allele sizes ranging from 203.6-334 bp. The SSR markers allocated genotypes into two distinct clusters close to the phenotypic markers. Forty sorghum hybrids were developed through a line by tester mating design involving 10 lines selected for their compatibility with F. oxysporum and high agronomic performances and four Striga resistant tester parents. The F1s and their parents were field evaluated with complementary in-vitro tests. Field evaluations were conducted at two locations: Kobo and Shewa Robit in Ethiopia, which are well known for their severe Striga infestation. Significant (p<0.05) general combining ability (GCA) effects were observed among testers and lines at both sites for days to 50% flowering and maturity, plant height, biomass, number of Striga plants and Striga plant height. Furthermore, significant (p<0.05) specific combining ability (SCA) effects were detected for days to 50% flowering, biomass, grain yield and number of Striga plants. From the complementary in-vitro experiment, highly significant variation (p<0.01) was exhibited due to line x tester interaction for maximum Striga germination distance. The study identified paternal parents with high GCA effects including SRN-39 and Birhan and maternals 235761, 2384443, IC9830, 235466, 237289,235763, and 235929 to be useful for breeding for ISM in sorghum. At Kobo, cross 235763 x N-13 and Shewa Robit IC9830 x SRN-39 had significantly negative SCA effects for the numbers of Striga plants. Progenies of these crosses will be selected in the Striga resistance breeding program. In the participatory sorghum genotypes assessment, farmers were invited to assess and select the genotypes based on their preferences at maturity and harvesting. The standard agronomic traits and Striga parameters relevant for breeding were collected by the breeders. Earliness, Striga resistance, high yield and high grain quality and threshability were the most important farmers‟-preferred traits for sorghum genotypes. Comparative analyses between farmers‟ and breeders‟ evaluations revealed highly significant correlations (p<0.01) except between Striga resistance and Striga damage and pest resistance and insect damage. Repeatability of scoring genotypes among farmers was consistent (>0.80) for all traits except Striga and pest resistance. The prioritized traits through farmers‟ participation are important for further breeding program. Overall, the study established farmers‟ preferred traits, the effectiveness of ISM to boost sorghum productivity, and identified useful parents and crosses for effective sorghum breeding to control Striga in Ethiopia. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 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.