The enrichment of B-carotene, a precursor to vitamin A, in the local sweetpotato (Ipomoea batatas L.) cultivars is an attractive option in order to improve vitamin A intake in Zambia. The study was conducted to: 1) identify sweetpotato genotypes high in B-carotene content and high root dry mass (RDM) and to determine their combining ability, as measured through their progeny performance; and 2) screen progeny for root characteristics, yield, B-carotene content, and RDM. Firstly, a participatory rural appraisal (PRA) was conducted to determine the consumer preferences for sweetpotato. These preferences would form the basis for selecting desirable genotypes. Secondly, five selected parents were crossed in a full diallel for genetic variance studies. A selected subset of the diallel progeny were evaluated in three environments. Thirdly, 15 polycross progeny were evaluated for stability in five environments using additive main effect and multiplicative interaction (AMMI). The PRA revealed that consumers preferred high RDM combined with high fresh root yield. The diallel crosses recorded significant general combining ability (GCA) and specific combining ability (SCA) effects for B-carotene, RDM, harvest index (HI) and root fresh yield (RFY). The ratios of GCA to SCA variances were large (0.68-0.92). Two high B-carotene parents exhibited positive high GCA effects, indicating that additive gene effects were predominant in the inheritance of B-carotene. Reciprocal mean squares were not significant for RDM but they were significant (p=0.01) for B-carotene content. The estimate of narrow sense heritability of RDM (76.3%) was high; but heritability of B-carotene (20.9%), HI (29.1%) and RFY (34.9%) were much lower. These results suggest that rapid genetic gains should be possible with mass selection breeding techniques based on the phenotype of the parent for RDM but progress will be slow for B-carotene content HI, and RFY. The AMMI analysis identified progeny G2 (B-carotene content = 5.0 mg 100 g-1 and RDM = 37%), G6 (B-carotene content = 4.7 mg 100 g-1 and RDM = 37%), and G8 (B-carotene content = 4.7 mg 100 g-1, RDM = 35%) from the polycross as stable across environments for both B-carotene content and RDM. Genotype G3 was best suited to one of the test environments and had the highest B-carotene content (9.421 mg 100 g-1) and a high RDM (35.47%). / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Reduced banana yield owing to black Sigatoka Mycosphaerella fijiensis Morelet is a threat to the livelihoods of Ugandan subsistence farmers who depend entirely on the banana crop for food security. The objectives of this investigation were to: (i) assess farmers’ knowledge of black Sigatoka disease in central Uganda; (ii) document the qualities farmers would desire in the banana genotypes to be developed for black Sigatoka resistance; (iii) appraise the methods for assessing black Sigatoka resistance in diploid banana populations; (iv) determine the phenotypic variation for black Sigatoka resistance and agronomic traits in diploid and tetraploid bananas; (v) determine the influence of tetraploid and diploid parents on the black Sigatoka resistance and agronomic traits in the triploid progenies; and (vi) evaluate 2x by 2x banana progenies for yield and black Sigatoka resistance. A survey that focused on low and medium banana production zones in Uganda established that there was limited awareness of black Sigatoka disease as a constraint on banana production in the areas surveyed. It was also established that farmers liked local bananas because of their superior taste, early maturity, and marketability. There were farmers who had been exposed to new black Sigatoka resistant materials but never liked these new banana materials because of poor taste and lack of market. Farmers desired new banana materials with good taste on cooking, heavy bunches, resistance to pests and diseases, drought tolerance, and early maturing capacity in that order. The results indicated that the banana farmers in Uganda attached more importance to food quality attributes than to production attributes especially when considering new banana materials. This suggested that farmers mainly grow bananas for consumption. Three black Sigatoka assessment methods, youngest leaf spotted, disease development time and area under disease progress curve (AUDPC) were appraised using a diploid population. All the three methods were able to classify the diploid accessions into resistant and susceptible clones. The cultivar rankings of AUDPC correlated strongly with the rankings of disease development time. The cultivar rankings of AUDPC correlated positively with the rankings of youngest leaf spotted method. The youngest leaf spotted at flowering and AUDPC predicted significantly total number of leaves at flowering (R2 = 0.53). Overall AUDPC had the highest coefficient of determination (R2=0.84) in assessment of banana diploids for black Sigatoka resistance indicating that it accounted for the highest variation in disease response observed among the diploid clones. From this investigation it was recommended that AUDPC should be used to assess resistance on black Sigatoka in Musa species. A phenotypic analysis on the diploid and synthetic tetraploids, and a molecular analysis using RAPD markers on the tetraploid population were conducted. Results indicated that the diploid population had significant (P<0.001) variation for plant height, plant girth, days from flowering to harvest, bunch weight, number of suckers, youngest leaf spotted, total leaves at flowering, area under disease progress curve, and number of functional leaves at harvest. Principal component analysis showed that plant height and girth explained most of the variation observed in the diploid population. In the tetraploid population, significant differences were observed for plant height, plant girth, and number of suckers (P<0.05). In the tetraploids principal component analysis, indicated that youngest leaf spotted and total leaves at flowering had higher loadings on principal component one. Genetic distances computed from RAPD markers indicated limited genetic variability in the tetraploid population. Another investigation was also carried out to determine the influence of tetraploid and diploid parents on black Sigatoka resistance and agronomic traits in the triploid progenies generated from tetraploid-diploid crosses. The results indicated that diploids transferred black Sigatoka resistance to triploid progenies as measured by disease development over time, the number of functional leaves at flowering and at harvest. On the other hand, the female synthetic tetraploids influenced plant height and bunch weight in the triploid progenies generated from tetraploid-diploid crosses as observed from triploid progeny correlations and parent-offspring regressions. Therefore, it is important to select tetraploids with heavy bunch weights to generate high yielding triploids in tetraploid-diploid crosses. Lastly, this thesis investigated the relationship between bunch weight and black Sigatoka resistance traits in 2x by 2x progenies generated using a random polycross design. Phenotypic correlations revealed strong positive relationships between bunch weight with total leaves at flowering, youngest leaf spotted, plant girth, and days from planting to flowering among the 2x by 2x progenies. Linear regression analysis indicated that girth, total fingers and finger length significantly predicted bunch weight (R2=0.67). However, days from planting to flowering, and total leaves at flowering had strong indirect effects on bunch weight via plant girth. The results imply that selection for parents with good combining ability for girth, finger length and total fingers can improve bunch weight in a diploid population. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009.

Maize (Zea mays L.) production is constrained by a number of stresses, amongst the most important are gray leaf spot (GLS) caused by a fungus Cercospora zeaemaydis Tehon and E.Y. Daniels and Phaeosphaeria leaf spot (PLS) caused by Phaeosphaeria maydis (Henn.). The diverse germplasm comprising farmer collections and exotic material used in the medium and highland altitudes maize breeding programmes in western Kenya has not been improved for resistance to the two diseases. Heterotic patterns of germplasm from this region have also not been studied. Therefore, the objectives of this study were to (i) assess the prevalence, importance, and farmers’ perceptions of GLS and PLS, (ii) characterize maize germplasm collections into their heterotic groups and (iii) improve four maize populations for GLS and PLS resistance through recurrent selection. The participatory rural appraisal (PRA) was conducted at three sites in western Kenya during the 2005/2006 cropping season. Data was generated using a checklist in group discussions with 109 male and 123 female farmers as well as key informants. Constraints were identified and prioritised. The five most limiting, in order of importance, were low soil fertility, poor varieties and seed, drought, Striga, pests and diseases (GLS and PLS). Gray leaf spot and PLS were reported in all sites but farmers did not know the causes of these diseases. Farmers preferred local varieties Tiriki, Anzika and Kipindi due to their greater resistance to diseases than commercial hybrids. Farmer criteria for variety selection were low fertilizer, Striga and disease resistance, drought tolerance, closed tips, and high yield potential. Due to the high cost of hybrid seed farmers selected and planted their own seed from advanced generations from previous seasons. Across all the sites, yield gap between on-farm and expected yield potential was estimated as ranging from 4.73t ha-1 to 5.3t ha-1 mainly due to the identified constraints. Therefore maize breeding should focus on addressing important maize production constraints and farmers’ preferences identified in this study in developing varieties that will increase maize yields on-farm. During 2005/2006, seventy 77 testcrosses were developed through crossing 47 germplasm collections with four population testers, Kitale synthetic II (KSII), Ecuador 573 (EC 573), Pool A and Pool B. Crosses and testers were evaluated at Kakamega during 2006/2007 in a 9 x 9 triple lattice design. Significant (p < 0.05) differences in grain yield, ear height, days to 50% anthesis, GLS and PLS resistance were observed. Both general and specific combining ability effects (GCA and SCA, respectively) were significant (p < 0.01), with SCA accounting for more than 50% of the variation for GLS, PLS and yield and less than 50% for ear height, days to 50% anthesis and silk. This indicated that both additive and non-additive gene effects were important but non-additive gene effects were more important in conditioning these traits. High SCA effects indicated high heterosis between collections and populations. Both yield heterosis and SCA were used to study heterotic patterns, but percentage yield heterosis data was used to classify these materials into heterotic groups. Based on significance (p < 0.05) of percentage yield heterosis as a primary factor for classification, seven collections were classified to Pool A, 17 to Pool B, 12 to KSII and 6 to EC 573 heterotic groups. The study indicated that germplasm collections belong to distinct heterotic groups therefore they can be infused into these populations (Pool A, Pool B, KSII and EC 573). Four populations, KSII, EC 573, Pool A and Pool B were subjected to one cycle of reciprocal recurrent selection (RRS) and two cycles of simple recurrent selection (SRS) during the 2004-2006 cropping seasons at Kakamega. Response to selection was assessed by evaluating C0, C1 and C2 and four commercial checks in a randomised complete block design in three replications at Kakamega and Kitale during 2007. All cycles except C0 of Pool A were more resistant to GLS than the three checks, H623, KSTP94 and PHB3253. Response to selection for GLS was significant (p < 0.01) in the desired direction. Gains ranged from -32.2% to 6.4% cycle-1 for RRS and 0.0% to -61.3% cycle-1 for SRS. Heritability estimates of between 59% and 76.3% for GLS and 39% and 80% for PLS were observed indicating that both GLS and PLS can be improved through selection. Significant negative correlations between GLS and yield were observed in Pool A C0 (r = -0.947, p < 0.01) and between yield and PLS in Pool A C0 (r = -0.926, p < 0.01). These indicated gain in yield as GLS and PLS were selected against. Generally, SRS out performed RRS method both in genetic gain and time, as indicated by gain of -61% for SRS and -32.2% for RRS, respectively. Two cycles of selection were achieved in two years with SRS as compared to only one with RRS. These results clearly demonstrated that it is possible to improve for GLS resistance using simple and reciprocal recurrent selection methods. The main constraints to maize production in Western Kenya were low soil fertility, Striga, drought, lack of seed and diseases. Farmers preferred varieties that can do well under the constraints mentioned. Local collections belonged to distinct heterotic groups with good resistance to GLS and PLS and were highly heterotic to four maize population testers with both SCA and GCA effects being important in conditioning GLS and PLS resistance. Recurrent selection methods were found to improve maize resistance to GLS and PLS. Breeding should therefore, focus in development of hybrids and improvement of populations using these local collections by employing SRS and RRS selection methods with identified constraints and farmer preferences in mind. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2007.

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.

Viral diseases are a major limiting factor to cowpea production in many countries of Africa. In Uganda, studies indicated that the cowpea aphid-borne mosaic virus (CABMV) is common and a potential threat to cowpea production in the region. There have been no efforts to develop cowpea cultivars with resistance to CABMV in Uganda. This work focused on the development of cultivars resistant to CABMV. Production of cowpea in Uganda is constrained by several factors, including a lack of awareness of diseases among the majority of farmers. A participatory rural appraisal (PRA) was conducted to elicit farmers’ indigenous knowledge of cowpea production and also to gain insight into their understanding of viral diseases affecting cowpea in Uganda. PRA tools such as group discussions, transect walks, problem listing and ranking were used to gather information. Insect pests, diseases, low yielding cultivars and the high cost of pesticides were perceived to be the most important production constraints. Farmers were not aware of the problem of virus diseases, but provided descriptive names of symptoms. Only three cowpea cultivars (Ebelat, Ecirikukwai and Blackcowpea) were produced in the area. Seed size and colour were seen as important traits in new varieties. Information about the occurrence, distribution and identity of cowpea viruses is limited in Uganda. The objective of this study was to identify the important cowpea virus diseases occurring naturally in the major cowpea growing regions of Uganda. Surveys were conducted to determine the incidence and severity of virus symptoms in four districts (Soroti, Kumi, Pallisa and Tororo) in 2004 and 2005. The incidence ranged from 40.5 to 94.4% and severity ranged from 15.0 to 30.6% (for Kumi and Pallisa districts, respectively) during the 2004 surveys. In 2005, the incidence ranged from 55.9 to 85.4% and severity ranged from 4.7 to 14.5% (for Tororo and Soroti districts, respectively). The CABMV, cowpea mild mottle virus (CPMMV), cowpea severe mosaic virus (CPSMV) and cucumber mosaic virus (CMV) were serologically detected by double antibody sandwich enzyme- linked immunosorbent assay (DAS-ELISA). Fifty four improved cowpea genotypes were screened for resistance to CABMV during the first season of 2004 at Serere Agricultural and Animal Production Research Institute in Uganda. Further screening was conducted in the second season of 2004 using 27 genotypes. The genotypes were planted in single rows between the rows of the susceptible cultivar, Ebelat. This was to provide high pressure of aphid vector (Aphis craccivora Koch) and CABMV inoculum. In addition, the test genotypes were artificially inoculated with a CABMV extract on fully expanded primary leaves of fourteen day-old seedlings. The CABMV incidence and severity was assessed. Disease severity was assessed on a 0-60% visual estimation scale where 0 = with no symptoms and 60 = with severe symptoms. Serological analysis was conducted using DAS-ELISA. Five genotypes showed good levels of resistance to CABMV, namely MU-93, IT82D-889, IT82D-516-2, IT85F-2841 and SECOW-2W. These resistant lines were crossed with three susceptible local landraces, namely Ebelat, Ecirikukwai and Blackcowpea in a North Carolina II mating design. The F1, F2 and BC1F1 populations and the parents were evaluated in the field to assess the response to CABMV and to study the inheritance of resistance to CABMV. The general combining ability (GCA) and specific combining ability (SCA) effects were significant, indicating that both additive and non-additive genetic factors are important in determining the control of CABMV in cowpea. The proportions (%) of the sum of squares for crosses attributable to GCA and SCA for CABMV severity were 51.4% for GCA due to females, 8.4% for GCA due to males and 40.2% for the SCA. The narrow-sense heritability estimates, obtained by regressing F1 on mid-parents was 0.87 and 0.84, F2 on F1 progenies 0.49 and 0.48, and F2 progenies on mid-parents 0.63 and 0.79, for AUDPC and final disease severity, respectively. Single gene conditioned resistance in seven populations, but resistance was quantitatively inherited and involved many genes in eight populations. Observation of transgressive segregation and moderate to high heritability suggests a quantitative mode of gene action and the importance of additive effects. The predominance of GCA variance, high heritability estimates and observation of transgressive segregation suggested that resistance could be improved by selection. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Dry bean (Phaseolus vulgaris L.) is economically and nutritionally an important legume, not only in Malawi, but in many parts of Africa and Latin America. Unfortunately, two bruchid species (Acanthoscelides obtectus Say, and Zabrotes subfasciatus Boheman) are known to cause extensive damage in storage, reducing the economic importance, food value and planting value of the crop. The aim of this study was to: i) ascertain farmers’ perceptions of the importance of bruchids as storage pests, and to identify their preferred varietal traits in dry beans; ii) screen Malawian dry bean landraces for effective and adaptable sources of resistance to the two bruchid species; iii) determine the gene action and inheritance of bruchid resistance. Farmers’ perceptions on the importance of the two bruchid species to beans both in the field and in storage were established using a participatory rural appraisal (PRA) in three extension planning areas (EPAs) in Lilongwe agricultural development division (ADD). Results confirmed that the two bruchid species are important storage pests, causing serious storage losses among smallholder farmers. In the absence of any control measures, farmers indicated that more than 50% of their stored beans could be lost to bruchids. Indigenous bruchid control measures are not very effective, making it necessary to search for other control methods. It was also clear from the PRA results that breeders need to consider both agronomic and culinary traits in bean cultivar development. This would enhance uptake of newly developed varieties. To address the problem of bruchid damage experienced by smallholder farmers, a total of 135 dry bean genotypes, comprising 77 landraces and 58 improved varieties (obtained from collaborating partners) were tested under laboratory infestation (nochoice test methods) and field infestation (free-choice test methods). The objective of this study was to identify effective sources of resistance to the two bruchid species. Results of the study showed that there was a wide variation among the genotypes for resistance to the two bruchid species. Overall results showed that 88% of the genotypes ranged from susceptible to highly susceptible to Z. subfasciatus and only 12% of the genotypes were moderately resistant to resistant. Genotype screening for resistance to A. obtectus showed that only 12.5% were resistant, whereas 87.5% were moderately to highly susceptible. All of the improved genotypes were 100% susceptible to A. obtectus in storage. One landrace, KK35, consistently showed a high level of resistance to both bruchids under laboratory infestation, with results similar to the resistant checks (SMARC 2 and SMARC 4), while another landrace, KK90, displayed stable resistance under both laboratory and field infestation. However, performance of most genotypes was not consistent with field and laboratory screenings, suggesting that mechanisms of bruchid resistance in the field are different from that in the laboratory and field screening should always be used to validate laboratory screening. Resistance in the field was not influenced by morphological traits. The seed coat played a significant role in conferring resistance to both bruchid species in the laboratory, whereas arcelin did not play any significant role in conferring resistance in the landraces. The inheritance of resistance to A. obtectus was studied in a 6 x 6 complete diallel mating design, involving crosses of selected Malawian dry bean landraces. The F1 crosses, their reciprocals, and six parents were infested with seven F1 generation (1 to 3 d old) insects of A. obtectus in a laboratory, no-choice test. There were significant differences among genotypes for general combining ability (GCA) and specific combining ability (SCA). However, SCA accounted for 81% of the sum of squares for the crosses, indicating predominance of the non-additive gene action contributing to bruchid resistance. A chi-square test for a single gene model showed that 5 of the 13 F2 populations fitted the 1:2:1 segregation ratio of resistant, intermediate and susceptible classes, respectively indicating partial dominance. The eight F2 populations did not conform to the two gene model of 1:4:6:4:1 segregation ratio of resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible classes, respectively. Average degree of dominance was in the partial dominance range in five F3 populations, but in general resistance was controlled by over-dominance gene action in the F2 populations. The additive-dominance model was adequate to explain the variation among genotypes indicating that epistatic effects were not important in controlling the bruchid resistance. The frequency distribution of the 13 F3 populations for resistance to A. obtectus provided evidence for transgressive segregation, suggesting that resistance is conditioned by more than one gene. Reciprocal differences were not significant in the F2 generation seed; but were significant in four crosses in the F3 generation seed for adult bruchid emergence, suggesting that maternal effects or cytoplasmic gene effects also played a role in the inheritance of resistance to the common bean weevil. Through this study, important sources of bruchid resistance in dry bean have been identified in Malawian landraces (KK35, KK90 and KK73). These resistant sources will be used in a breeding programme to develop bruchid resistant bean cultivars, as well as improve resistance in susceptible commercial bean cultivars currently grown by farmers in Malawi. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Grain yield of rice can be enhanced by breeding for drought tolerance and optimum shattering. New generations of rice, the interspecific fixed lines known to carry more drought tolerance traits, are a potential source for improvement of the Ugandan landraces but they frequently carry genes for grain shattering. Information gathered through surveys to understand rice production constraints and farmers’ preferred rice traits are limited and they are generally unranked. The objectives of this study were seven-fold. They were to 1) determine farmers’ perceptions on the key production constraints and preferences for rice in Uganda, 2) develop and appraise cheap and efficient rice breeding equipment, 3) determine anthesis and the grain shattering pattern of rice, 4) characterize for drought tolerance and grain-shattering ability in rice populations in Uganda, 5) investigate crossability between O. sativa and the new interspecific fixed lines, and 6 and 7) determine the inheritance and gene action controlling drought tolerance and grain shattering traits. The experiments were conducted at Namulonge, Uganda, from 2006 to 2009. Data on farmer’s perceptions of the key production constraints and preferences for rice in Uganda were obtained through participatory rural appraisal (PRA) methods and a formal household survey of 380 farmers from three regions in Uganda during March 2007 to June 2008. The results showed that the variety NERICA 4 was the most preferred by farmers. Rice yellow mottle virus disease, rice blast and African rice gall midge were major constraints under lowland conditions, while drought was the major constraint under upland conditions. The preferred traits in traditional varieties included aroma characteristics, grain size and the texture of cooked grains. Cultivars that combine high yield potential, early maturity, drought tolerance, aroma characteristics and special market attributes should be included in the breeding objectives. A new anther suction device that uses an ordinary household vacuum cleaner was fabricated. Its overall units include a pipette tip, silicone tubing, hose tubes, a metallic stand, a rubber stopper and a household vacuum cleaner of 1600 w capacity. It is efficient, cheaper, less bulky and has lower replacement costs than the commercial one. In addition, a hand-held single grain tester, which is efficient, cheaper and more suitable for field studies than the laboratory tester, was developed and appraised. Studies to determine the grain-shattering pattern in rice were conducted by making assessments at 10, 20 and 30 days after anthesis. The results revealed that the highest level of discrimination among the varieties was between 10 days and 20 days after anthesis. Among the genotypes tested, NERICA rice attained anthesis earlier than CT rice and O. sativa attained anthesis later than both rice groups. Appropriate methods of planting the parental lines were proposed for pollination to be synchronised. Interspecific rice and O. sativa were characterized in the field for drought tolerance and grain-shattering ability. There was high variability wihin species in grain shattering and drought tolerance traits, suggesting that selection could be effective. The distribution of grain shattering scores was not normal, suggesting that some selection had taken place for the trait, unlike the drought tolerance traits and leaf roll scores where normal distributions were observed. Results of the crossability test between O. sativa and interspecific fixed lines revealed that some genotypes had high crossability when used as males, or as females, or as both females and males. The best male genotype combiners were CT 16334(2)-CA-2-M, WAB 365-B-1H1-HB and IRAT 257, while the best females combiners were CT 16334(2)-CA-11-M, CT 16317-CA-4-M and IRAT 325. In addition, additive effects were more important that non-additive effects for pollen viability and seed set in the crosses. Genotypes with acceptable crossability and varying levels of drought tolerance and grainshattering ability were selected for further studies. The selected genotypes were crossed in a North Carolina II mating scheme, and as pairs of crosses, and used to understand the genetic mechanisms of drought tolerance at the reproductive and vegetative stages. Evaluation of the populations revealed that additive effects for filled grains were more important under drought stress and non-drought stress conditions than the non-additive effects. There were high heritability estimates for leaf roll under drought stress, implying that additive effects were more important. There was a higher contribution of additive effects for grain-shattering ability than nonadditive effects in the populations. Allelic tests for the shattering trait revealed that a single gene was in 46% of the crosses; two genes in another 46% of the crosses had duplicate dominant effects as well as complimentary dominant/recessive effects; and there were three genes in four percent of the crosses. Segregation ratios of 3:1 and 1:3 were also found in two crosses. This could be due to a reversal of the function of the genes. Another surprising finding was that the segregation ratio of 3:1 was found in a cross with loose grain attachment to the pedicel in an allelism test. This segregation was probably due to unfixed loci in some of the interspecific lines. This study identified rice breeding priorities for Uganda, prepared breeding tools and provided relevant information for generating lines that have improved drought tolerance and optimum grain-shattering ability by determining the modes of gene action for these two traits. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Finger millet (Eleusine coracana (L.) Gaertn. ssp. coracana) is an important food, food security and cash crop in eastern and southern Africa where small-scale farmers grow it in low input farming systems. The crop has food security, nutritional, cultural, medicinal, and economic value with high industrial potential. Little research and hardly any breeding have been done on the crop leading to low yields and low production. A project was therefore implemented in western Kenya during 2004-2007 seasons to investigate the possible breeding contributions to enhance productivity and production of the crop. The research comprised a social survey, germplasm evaluation, appraisal of ethrel as a chemical hybridising agent (CHA), genetic analysis of yield, and resistance to blast and Striga, and breeding progress in developing new finger millet varieties. A participatory rural appraisal (PRA) was conducted in three districts during 2006 to position finger millet (FM) in the farming systems, production constraints, and variety diversity and farmer preferences. The PRA established the high rating the peasant farmers gave to finger millet among crop enterprises, using it for food, cash, brewing, ceremonies and medicinal purposes. Farmers cultivated many varieties ranging from five to nine in a district, but each district had its own popular variety. Farmers used the following criteria to select new cultivars: high yield potential; early maturity; resistance to blast disease, Striga, birds, drought, and lodging; large head size, dark grain colour, and good taste. This probably indicated the willingness of farmers to adopt new varieties. Farmers identified constraints to production as blast disease, Striga, wild FM, birds, rats, termites, lack of market, labour shortage, and low yield. The farmers’ variety selection criteria and production constraints underscored the need to improve finger millet varieties. Evaluation of 310 accessions for trait variability and association conducted during 2005 long rain (LR) season at two sites revealed wide variation among the accessions for yield and secondary traits. The best accessions grain yield was above the yield potential of 5,000- 6,000kg ha-1 reported in other environments. Accessions KNE 072 (7,833kg ha-1), GBK 028463 (7,085kg ha-1), GBK 029661 (6,666kg ha-1) and FMBT ACC#42 (6,566kg ha-1) were outstanding. The data showed the opportunity to select for yield directly because of its wide variability but indirect selection could also be used to exploit seedling vigour as shown by its high correlation to yield and direct and indirect positive effects on yield through plant height and single plant yield in path analysis. The wide genetic variability among the genotypes for several traits indicated high potential to breed new and better finger millet varieties. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Rice (Oryza sativa L.) is the principal crop of North Eastern Tanzania but production is threatened by salt affected soils, drought and the use of un-adapted cultivars, among other constraints. Little research and hardly any breeding have been done on the aspects of salt tolerance of the crop in sub Saharan Africa, leading to low yields and low production in rice irrigation schemes under arid and semi arid conditions. A project was therefore implemented in North Eastern Tanzania during 2007-2010 seasons to investigate the possible breeding contributions to enhance productivity and production of the crop in salt affected areas. The objective of this study was to: a) determine farmers’ perceptions on both salt problems and their effects on rice crop productivity as well as establishing farmers’ needs and preferences for rice varieties in the targeted irrigated environment; b) determine the extent of salt problem in both soil and irrigation water in the available rice irrigation schemes in the North-eastern Tanzania; c) identify the major physiological mechanisms associated with salt tolerance in farmer-preferred native varieties and landraces; and d) determine the mode of inheritance of salt tolerance in rice. Participatory rural appraisal was conducted in Mkomazi and Mombo villages in Tanga region with the aim of understanding characteristics of rice–based farm economy, farmers’ perception of agriculture constraints and variety preferences in salt affected areas of North-eastern Tanzania. This was followed by a preliminary study to understand soil characteristics in relation to salt problems and its extent in selected nine rice irrigation schemes. Studies was established under controlled conditions to assess the salt tolerance of some rice farmers preferred rice cultivar and evaluate the putative traits in the rice materials that contribute to the performance of a genotype under saline and saline-sodic condition. Thereafter, genetic mechanism governing various morpho-physiological parameters in selected Tanzania local farmers’ preferred varieties and salt tolerant donors under saline and sodic soil conditions of North Eastern Tanzania were determined. A participatory rural appraisal (PRA) established that rice was a major staple food and cash crop and rice farming was a major economic activity in the area. However, soil degradation through increased salt affected soils was identified as the major factor responsible for irrigated rice yield decline. Major varieties grown are salt sensitive, and salt tolerant varieties were not available. The study also revealed that most farmers’ preferred traits of rice cultivars were high yield potential, aroma, early maturing, medium plant stature, tolerance to salt and drought. Improvement of these characters in new salt tolerant varieties would increase food production in fields with low or zero productivity and the well-being of the poor farmers. A soil characterisation study indicated the magnitude of the problem, whereby, seven out of nine studied irrigation schemes were affected and sodic and saline-sodic conditions were the dominant types of soils. Poor irrigation canals and management of irrigation water were the driving factors that contributed to salts accumulation causing a decline in productivity. Experiments were established under controlled environments to evaluate the tolerance of 10 and 11 rice genotypes under saline and saline-sodic stresses, respectively. Significant variation between genotype and significant interactions between genotype and salt treatment (P<0.001) were observed for all characters studied. Genotype Pokkalli, IR 67076-2B-21-2 and IR 56 showed superior performance under saline, whereas CSR 27, Nerica 2 and IR 56 had superior performance under saline-sodic. The study therefore established that, all the local farmer preferred cultivars except IR 56 performed poorly under both salt stress environments. High seedling vigour, less leaf injury, less Na+ and high K+ accumulation in leaves, low Na+/K+ ratio of ion uptake, high spikelet fertility, increased grains per panicle and 1000 grain weight were considered as the desirable characteristics therefore can be used in developing lines for salt tolerance for production under saline and saline - sodic conditions. Gene action and combining ability studies for nine morpho-physiological traits were studied under normal, saline and sodic soil environments. The rice populations were generated through 7 x 7 full diallel crosses and advanced to F2. The parents comprised two donors for saline tolerance, one donor for sodic tolerance and four salt sensitive farmers preferred varieties. Both additive and non-additive gene effects were important in the inheritance of the characters studied in all soil environments. However, additive effects were more important for the number of tillers, shoot Na+, Na+/K+ ratio and plant height. Both additive and non-additive gene effects were important for spikelet fertility, days to 50% flowering, number of grains per panicle, 1000 grain weight, and grain yield; however the magnitude of additive gene effect was higher than non additive effects. Amongst the parental lines, the best general combiners for yield along with other traits were TXD 306 and IR 67076-2B-21-2 under normal non-saline/sodic condition; IR 56, Pokalli and TXD 306 under saline condition and CSR 27 and TXD 306 under sodic conditions. The overall results from this study indicated the possibility of improving both yield and salt tolerance from this set of germplasm; therefore contributing to increasing rice yields in the marginal salt affected environments. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Maize (Zea mays L.) yields in the smallholder (SH) farming sector in Southern Africa have remained low. despite the availability of many improved varieties. Among the major constraints contributing to tow yields and threatening food security in the region are diseases which include grey leaf spot (GLS). common rust, northern corn leaf blight (NLB) and Phaeosphaeria leaf spot (PLS). These diseases are highly unpredictable in their occurrence every season, making them difficult to control. In addition, the majority of SH farmers cannot afford to control the diseases due to limited access to chemicals. Therefore, maize cultivars with high levels of disease resistance and tolerance to abiotic stresses would provide a long-term solution to addressing the problem of low yields, especially in the smallholder-farming sector. The objectives of this study were therefore to: i) establish farmers' perceptions on diseases, key limiting production constraints and preferred traits of maize cultivars. ii) screen germplasm adapted to tropical environments for resistance to PLS, iii) determine gene action for resistance to PLS and GLS, iv) estimate combining ability effects for resistance to PLS, GLS, NLB and common rust diseases, and v) determine grain yield stability of F, hybrids derived from crosses among selected tropical advanced maize inbred lines. These studies were conducted from 2006/7 to 2008/9 seasons at various sites in South Africa, Zimbabwe, Zambia and Uganda. Structured surveys and participatory rural appraisal (PRA) conducted in Obonjaneni. Busingatha and Okhombe villages of Amazizi district in the Northern Drakensberg established maize as the principal crop grown in the area. All the farmers who participated grew the local variety (landrace) they called Natal-8- row or Is/Zulu. The adoption of hybrids and improved open pollinated varieties (OPVs) was tow. Farmers preferred the local variety ahead of hybrids and improved OPVs mainly for its taste, tolerance to abiotic stresses and yield stability. Characteristics of maize varieties preferred by the farmers included: inexpensive seed, high yield, early maturity and tow input costs. Pests/d is eases and drought were not ranked highly, as farmers planted early to escape diseases and drought. Abiotic stresses were amongst the top four constraints faced by the farmers. The local varieties exhibited high yield potential and genetic variability fordisease resistance. Evaluation of maize germplasm adapted to tropical and subtropical environments of Africa for PLS resistance indicated significant (PS0.05) variation among the inbreds. populations and hybrids. In general, 63% of the inbreds/populations were resistant to PLS. Regionally important inbred lines; SC and N3 and CIMMYT's most successful lines such as CML395. CML444. CML202. CML312. and CML488 were resistant to PLS. Fifty- four percent of the single-cross experimental hybrids were also resistant to PLS. Correlation coefficients for area under disease progress curve (AUDPC) values for disease severity with PLS final disease severity scores were significant (P<0.001) and positive, implying that ranking of the genotypes for AUDPC and final PLS disease severity score was by and large similar. Forty five F, hybrids generated by crossing ten advanced maize inbred lines in a half diallel mating scheme were evaluated in two to six environments to determine combining ability, gene action and heterosis estimates for grain yield and resistance to PLS. GLS. NLB and common rust diseases. Highly significant (PS0.001) general combining ability (GCA) and specific combining ability (SCA) effects were observed for PLS. GLS. NLB. common rust, grain yield and other agronomic traits. The GCA effects were more important than SCA effects, indicating the predominance of additive over non-additive gene action for all the traits studied in these inbred lines. The inbred lines with good GCA for PLS resistance were: A12204, N3. A16. MP18 and CML488. and for GLS resistance were A1220-4. CZL00009. CZL00001. CML205 and CML443. Lines A16 and CML443 had good GCA for NLB and common rust resistance, lines A1220-4, N3, CML205, A16, and CML443 contributed towards high yield. Lines A1220-4 and A16 were late maturing, whereas CZL00009 displayed eariy maturity. High mid-parent and better-parent heterosis for high grain yield and resistance to all the diseases were observed. Generation mean analysis was used to deteimine the inheritance of PLS and GLS resistance in populations involving six tropical advanced maize inbred lines. Reciprocal crosses and backcross progenies were generated among inbreds A1220-4, A15, B17 (resistant. R), CML445 (moderately resistant. MR). CML441 and CZL00001 (susceptible. S) for PLS inheritance, and among inbreds A1220-4. A15, CML441 (resistant. R). and N3 and B17 (susceptible. S), for GLS inheritance. Results indicated highly significant additive effects (P<0.001) for PLS and GLS resistance, with dominance effects accounting forSH%of the variation in all the crosses for PLS and only A15 x B17 cross for GLS. Epistasis and cytoplasmic gene effects in favour of PLS resistance in F, crosses when the more susceptible parent was used as female were significant. For GLS resistance, epistasis was observed only in CML441 x N3 and A1220-4 x B17 crosses, while no cytoplasmic gene effects were detected. Resistance for PLS was medium to highly heritable and conditioned by less than four genes which exhibited incomplete dominance. In general resistance to GLS was controlled by two to three genes exhibiting zero to partial dominance and was moderate to highly heritable. Stability analysis of the hybrids was done over 11 environments using the additive main effects and multiplicative interaction (AMMI) and the genotype and genotype by environment (GGE) biplot analyses. Both AMMI and GGE biplot analyses selected hybrids H21 (CZL00009 x A16). H14 (A1220-4 x A16). S63 (SeedCo hybrid check). N72 (MP72/N3) and H26 (CZL00001 x A16) as stable and high yielding. Hybrids H1 (CML445 x A1220-4), H44 (CZL00009 x CML443) and H18 (CZL00009 x CZL00001) were identified by both methods as unstable but high yielding. AMMI and GGE biplot analyses identified ZAM08, C108, RAO9 and C09 as the most representative environments which were high yielding and relatively stable. In general, the study has revealed that based on the farmers ranking of the constraints in their area, breeding opportunities do exist for incorporating tolerance to both biotic and abiotic stresses in their varieties. It also identified maize lines resistant to the main foliar diseases, with good combining ability and heterosis for resistance and high grain yield. Hybrids with wide adaptation and high yields across environments were also observed. The experimental hybrids that exhibited high levels of resistance can be recommended for further testing and release. On the whole, highly significant additive effects and moderate to high heritability estimates observed for all the diseases and grain yield implied progress would be made through selection, although significant epistasis and dominance could slow progress. Dominance effects towards resistance and high yield could be exploited in developing single cross maize hybrids among these inbreds when only one parent is resistant. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.