Thesis (M.Sc (Plant Production)) --University of Limpopo, 2015 / Information on the performance of the maize and pigeonpea intercropping system under dryland conditions of South Africa is scanty. The aim of this study was to determine the optimum P level and productivity of pigeonpea and maize under the dryland intercropping system. Five P rates (0, 15, 30, 45, and 60 kg P ha-1) were applied to both sole and pigeonpea intercropped with maize in a randomized complete block design with 4 replicates. Growth parameters and yield and yield attributes of pigeonpea and maize were measured to determine performance of both crops. There were significant differences in grain yield of pigeonpea as influenced by P rates in both seasons. Highest grain yields of 781 kg ha-1 during 2009/10 and 894 kg ha-1 during 2010/11 were obtained at P rate of 45 kg ha-1. Cropping system significantly influenced grain yield of pigeonpea in 2010/11 season with 37.1% higher pigeonpea grain yield from intercropped plots than in sole pigeonpea plots. There was 21.8% increase in grain yield of pigeonpea across two seasons as influenced by P rate. Maize grain yield showed little response to P rate only during the first season. However, highest maize grain yield of 1699 kg ha-1 was obtained at 60 kg P ha-1 during the 2009/10 season. Maize grain yield was only significantly influenced by cropping system during the 2010/11 season where sole plots achieved higher grain yield of 4148 kg ha-1 compared to 3297 kg ha-1 from intercrop plots. The results revealed that P application increased grain yield of pigeonpea significantly, especially in intercropped plots. The calculated total land equivalent ratio (LER) for the two crops gave positive and higher than one values, which suggests a favourable grain yield advantage for maize/pigeon pea intercrop.

Thesis (M. A. Agriculture (Agricultural Economics)) -- University of Limpopo, 2021 / Maize seeds differ according to varieties.The traditional maize varieties(also referred to as (Landraces)are maize varieties that have been cultivated and subjected to selection by farmers for generations.They retain a distinct identity and lack formal crop improvement. Improved maize varieties,on the other hand,are bred with characteristics such as drought and disease tolerance. This research was conducted to determine the attributes preferred by farmers when making a maize varietal choice.To be specific, the study aimed to achieve the following objectives:(i) Identify and describe socio economic characteristics of smallholder maize farmers’ in Mogalakwena Municipality; (ii) Analyse socioeconomic characteristics of smallholder maize farmers in Mogalakwena Municipality; (iii) Identify different maize varieties grown by smallholder farmers in Mogalakwena Municipality,and (iv) determine and analyse factors influencing farmers’choice ofa maize variety. Descriptive statistics and the Multinomial Logistic Regression Model were used for data analysis.The results of the study revealed that 64% of the respondents had formal education.This meant that they have the capability to grasp more information, if provided with trainings. It was found that 75% of the farmers did not have access to extension service which is supposed to play a significant role in agricultural information dissemination.The most grown maize variety was land race varieties which constituted 59.5%. This percentage was said to be resultant from limited access to the seed market. Infact,80% of the farmers had to travel an average of 42 kilomteres to access the market which also had a limited number of varieties.The Multinomial Logistic Regression Model revealed that only 5 variables (Educational level, farm size, yield, extension contact and knowledge of maize varieties )were significantat1%,5%,1%,1% and1%, respectively.The majority of farmers were old people with little access to extension service and an inadequate farming knowledge which lead to a highper centage of farmers continuing to grow landrace varieties. Based on the findings, this study recommend further research on attributes that influence farmers varietal choice and Government intervention in provision for resources and development of existing and new infracstrcture to encourage extension service delivery. Keywords:Landrace,improvemaizevariety,smallholderfarmer

Maize (Zea mays L.) is an important crop in the world; however, its yield is compromised by new production challenges leading to poor yield in sub-Saharan Africa. This calls for a need to enhance maize adaptation to changing climate and challenging environments. The new maize varieties should be richly endowed with high frequency of genes that confer high yield under stress and non-stress conditions. Currently, such maize is not available, prompting research into development of new germplasm lines for use in developing new hybrids. The objective of the study was to determine i) the level of genetic diversity using SSR molecular markers and phenotypic data in a set of 60 maize inbreds from the breeding program, ii) genotype by environment interaction in maize hybrids, iii) cultivar superiority, iv) combining ability effects, v) the relationship between yield and secondary traits and vi) the relevant genetic parameters that underpin genetic gains in a breeding program. To study genetic diversity present in the germplasm, phenotypic data and 30 SSR markers were used to estimate the genetic distance between the inbreds. The results indicated that inbred lines which were put in the same cluster were related by pedigree and origin. To assess the level of genotype by environment interaction (GXE) and cultivar superiority of the new germplasm lines, hybrids were planted in five environments with two replications. Data were analysed using the REML and AMMI tools in GenStat 14th edition. The results revealed significant differences between hybrids and environments for grain yield. However, GXE interaction was also significant indicating possible challenges which can be encountered in selecting new hybrids. To determine combining ability estimates two different testers were used. The REML tool from GENSTAT was used to perform the line X tester analysis. Results indicated that both additive and non-additive gene action were important for grain yield. The direct selection strategy for yield was recommended because heritability of grain yield was high. Overall, results suggested that the information on genetic diversity will assist in defining heterotic groups; which will enable effective and efficient management of the germplasm lines to produce new maize hybrids. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Maize is Africa’s most important food crop. Unfortunately a yield gap currently exists in Africa which can be attributed to the use of inferior maize varieties such as open-pollinated varieties, double and three-way cross hybrids. Single cross maize hybrids, such as the world’s first commercial hybrid, SR52, have a higher yield potential, which is reflected by the doubling of maize yields in southern and eastern Africa by SR52, within a decade of its release. The main objective of this study was to determine the genetic basis behind SR52’s high yield potential and heterosis. This was established through a generation mean and path coefficient analysis of the SR52 maize hybrid. Research to determine genetic basis of yield and secondary trait was conducted using a randomized complete block design at two sites during the 2012/13 season, in South Africa. Six derivative generations of SR52 namely, its two parents N3 and SC, F1 and F2, and F1 backcross progenies (BC1N3 and BC1SC) were evaluated. A generation mean analysis was performed using PROC GLM procedures in SAS computer software program. High levels of mid-parent heterosis for grain yield potential was confirmed and ranged from 140% at Cedara to 311% at Ukulinga. The additive-dominance model was not adequate to explain the yield potential of SR52. Although negligible (less than 10%), epistatic gene effects were also influential (P<0.01) on grain yield and its components in SR52. The dominance and additive gene effects were highly significant (P<0.01), but dominance effects were the most influential. Correlation and path coefficient analysis of SR52’s segregating F2 and BC1 populations was performed in SAS. Most secondary traits, such as ear mass, ear length, total number of kernels per ear and plant height, were significant (P<0.05) and positively correlated with yield. However, the ear length, number of kernel rows, kernels per row and 100-kernel mass displayed the largest direct effects on yield of SR52, while indirect effects of secondary traits were small. The presence of genetic variation, as well as transgressive segregants for the yield components indicates possibility for extracting new germplasm lines with the desired QTL’s. It is concluded that SR52 is such an exceptional hybrid because of dominance gene action and direct contribution of superior cob length, number of kernel rows and mass of kernels to yield. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Maize is the principal crop for food security and livestock feed in South Africa. It is also an industrial crop and the produce is exported to many countries in the world. Therefore there is high seed demand which prompts competition for breeding productive hybrids. However direct introduction of tropical hybrids into the warm temperate South African environments has not been successful. Competitive advantages can be obtained by implementing a “shuttle breeding” programme whereby part of the breeding is done in Zimbabwe and South Africa to minimise research and production costs. Introgression of temperate germplasm in tropical elite inbred lines can also be pursued to obtain adapted hybrids. The aim of this study was therefore to assess the effectiveness of introgression of temperate germplasm into tropical elite maize inbred lines as a strategy to enhance adaptability of new hybrids to South Africa, and also to determine both breeding and economic value of a “shuttle breeding” programme. To this end, the introgressed inbred lines and their hybrid progenies were evaluated in South Africa to determine the effect of the selection environment on their performance and genetic variation. Both genetic and economic gains were evaluated with a view to make recommendations to the small and medium scale enterprises with interests in the market. Introgression of temperate germplasm into tropical germplasm elite lines did not disrupt the heterotic groupings because most of the introgressed lines (86%) fitted into known existing heterotic groups. Only 14% of the introgressed lines did not show any inclination to towards the known heterotic clusters of their founder tropical parents. These lines were considered to be new recombinant inbred lines that showed little resemblance with their founder parents. Selection environment did not influence heterotic clustering of the introgressed lines, and genetic diversity was identified among introgressed lines developed in the same environment. Genetic variation was observed for the major economic traits and heritability of 21% to 91%. The introgression was effective for improving grain yield potential and ear prolificacy. Spearman’s rank correlation analysis on grain yield and ear prolificacy data showed significant positive correlation between selection environments such as Ukulinga in South Africa and Kadoma Research Centre in Zimbabwe. Therefore Kadoma Research Centre will be recommended for use in breeding new maize germplasm lines for South Africa. Correlation among traits showed that ear prolificacy and plant height had significant (P<0.05) direct effects on grain yield thus direct selection of these traits will be emphasised in breeding new hybrids. Introgression of temperate germplasm into tropical elite maize inbred lines was effective for improving their adaptation to warm temperate environments. Positive genetic gains of 5-58% were realised for grain yield potential and 26-46% for ear prolificacy. Whereas 1% to 37% gains were realised for secondary traits such as plant and ear height, anthesis and silking days there was barely any improvement for root and stalk lodging, and grain moisture content at harvest. However, introgressed lines displayed impressive performance per se and inter se indicating potential for commercial production. The new inbred line 71-DMLF7_88 combined early physiological maturity, high ear prolificacy and grain yield potential qualifying it as a perfect parent for the warm temperate environments. At least six hybrids were stable and adaptable while four were considered to be ideal genotypes relative to standard commercial hybrids such as PAN6Q445B which is a market leader. The exceptional hybrids, 12C20264, 12C22766, 13XH349 and 11C11774 will be advanced in South Africa. The study also indicated significant economic gains when a shuttle programme is implemented to breed new hybrids following the introgression strategy. The “Shuttle breeding” programme attained a positive net present value (NPV) of $1, 834, 166. 00. This indicated an increase in shareholder value through an opportunity cost of 17% and 3% relative to conventional breeding programmes which are based in South Africa and Zimbabwe, respectively. Positive NPV and genetic gain achieved using the “shuttle breeding” programme makes it a viable option for small and medium scale seed companies with intention to breed and commercialise competitive products in South African. In general, the study revealed that introgression of temperate germplasm into tropical elite inbred lines using a “shuttle breeding” programme was effective for enhancing adaptability of tropical germplasm to the South African warm temperate environments. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Thesis (M. A. Agricultural Science (Agricultural Economics)) -- University of Limpopo, 2021 / Maize seeds differ according to varieties. The traditional maize varieties(also referred to as (Landraces)are maize varieties that have been cultivated and subjected to selection by farmers for generations. They retain a distinct identity and lack formal crop improvement. Improved maize varieties, on the other hand, are bred with characteristics such as drought and disease tolerance. This research was conducted to determine the attributes preferred by farmers when making a maize varietal choice. To be specific, the study aimed to achieve the following objectives:(i) Identify and describe socio economic characteristics of smallholder maizefarmers’ in Mogalakwena Municipality;(ii) Analyse socioeconomic characteristics of smallholder maize farmers in Mogalakwena Municipality;(iii)Identify different maize varieties grown by smallholder farmers in Mogalakwena Municipality, and (iv) determine and analyse factors influencing farmers’ choice of a maize variety. Descriptive statistics and the Multinomial Logistic Regression Mode lwere used for data analysis. The results of the study revealed that 64% of the respondents had formal education. This meant that they have the capability to grasp more information, if provided witht rainings. It was found that 75% of the farmers did not have access to extension service which is supposed to play a significant role in agricultural information dissemination. The most grown maize variety was landrace varieties which constituted 59.5%. This percentage was said to be resultant from limited access to the seed market. Infact, 80% of the farmers had to travel an average o f42 kilomteres to access the market which also had a limited number of varieties. The Multinomial Logistic Regression Model revealed that only 5variables (Educational level, farm size, yield, extension contact and knowledge of maize varieties) were significant at 1%, 5%,1 %,1% and1%, respectively. The majority of farmers were old people with little access to extension service andaninad equate farming knowledge which lead to a high percentage of farmers continuing to grow landrace varieties. Based on thef indings, this study recommend further research on attributes that influence farmers varietal choice and Government intervention in provision for resources and development of existing and new infracstrcture to encourage extension service delivery Keywords: Landrace, improve maize variety, smallholder farmer

Maize (Zea mays L.) is one of the most important food crops in sub-Saharan Africa (SSA); however its production is constrained by many factors. Grain yield is compromised by poor genetic performance and poor agronomic management. This calls for need to develop hybrids and exploiting heterosis of single crosses which are adapted to challenging environments. Currently, there is no popcorn hybrids developed in South Africa which is adapted to local conditions. As such, there is need to develop hybrids that cater for smallscale farmers in marginal environments. The objectives of the study were to determine i) standard heterosis, levels of variation and heritability for phenotypic traits in dent and flint maize hybrids; ii) the association between genetic distances and phenotypic traits in dent and flint maize hybrids; iii) mid-parent heterosis in popcorn hybrids, iv) the effect of secondary traits on grain yield in dent, flint and popcorn hybrids; v) genetic diversity and the relationship between traits in widely grown selected hybrids in Southern Africa; and vii) to compare effectiveness of phenotypic analysis models for determining genetic distances between hybrids. Popcorn, dent and flint hybrids were evaluated at two sites. The data was analysed using SAS, Genstat and Power marker statistical packages. The results revealed that the relationship between genetic distance and heterosis is dependent on the environment. Hybrids in top 10 at both sites were different indicating that there was a significant genotype x environment interaction. 13 new heterotic patterns that performed better than the controls can be utilized in heterosis breeding; however there is need to test them in different environments to check on their stability. Grain texture cannot be used to discriminate hybrids for yield because all patterns of dent x dent, dent x flint and flint x flint were present in the top 10 hybrids. Lines DXL124 and DXL158 dominated parentage of the top 10 hybrid rank for yield qualifying them as potential testers for specific combining ability in future studies. Heterosis in popcorn hybrids that performed better than the mid-parent can be utilized in heterosis breeding to exploit vigour, though there is need to test the hybrids in a number of different environments. The main direct factors contributing to yield were ear prolificacy, ear aspect, number of plants and shelling percentages qualifying them to be selected to boost grain yield. Phenotypic data and 91 SNP markers were used to estimate the genetic distance between the hybrids. The results indicated that hybrids that were in the same cluster belong to the same brand and were related in origin and pedigree. Both molecular and phenotypic data were effective in discriminating the hybrids into different clusters according to genetic background. SNP markers revealed nine clusters of hybrids, 12-trait model revealed eight clusters and five-trait model revealed six clusters at 85% genetic distance. The study indicates strategies that can be adopted to boost grain yield in dent, flint and popcorn hybrids. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Maize (Zea mays L.) is the third most important cereal crops in the world after wheat and rice. In Ethiopia, maize remains the second largest food security crop after tef [Eragrostis tef (Zucc.) Trotter.]. The mid-altitude, sub-humid agro-ecology (1000 to 1800 m above sea level) is the most important maize producing environment in Ethiopia. However, productivity of maize is low, due to several biotic and abiotic constraints. Among the biotic constraints, Turcicum leaf blight disease of maize caused by Exserohilum turcicum Pass Leonard & Suggs shows high incidence of 95-100% and inflicts significant grain losses in the country. Therefore, high yielding, Turcicum leaf blight resistant and farmers-preferred maize varieties and their production technologies should be developed and made available to growers to enhance maize production and to achieve food security. The objectives of this study were to: (1) assess farmer’s preferences, and production constraints for maize in the mid-altitude, sub-humid agro-ecology of western Ethiopia, (2) determine the genetic variability among elite maize inbred lines and select promising parents for resistance to E. turcicum, (3) determine diversity among the elite germplasm lines using SSR markers, (4) determine combining ability and heterosis among elite maize inbred lines and their hybrids, and (5) investigate genotype x environment interaction and yield stability of experimental maize hybrids developed for the midaltitude sub-humid agro-ecology of Ethiopia. A participatory rural appraisal (PRA) research was conducted involving 240 maize farmers in three representative maize growing zones of western Ethiopia; West Shoa, East Wollega and West Wollega, each represented by two districts and two subdistricts. Maize was ranked number one both as food and cash crop by 82.9% of respondents. Turcicum leaf blight was ranked as number one devastating leaf disease by 46% of respondents. Breeding for improved disease resistance and grain yield, enhancing the availability of crop input and stabilizing market price during harvest time were recommended as the most important strategies to increase maize production by small-scale farmers in western Ethiopia. Fifty inbred lines were evaluated for reaction to Turcicum leaf blight during the main cropping seasons of 2011 and 2012. Inbred lines were clustered into resistant (CML202, 144-7b, 136-a, 139-5j, 30H83-7-1, ILOO’E-1-9, SZYNA-99-F2, and 142-1-e), and susceptible (CML197, CML464, A7033 , Kuleni C1-101-1-1, CML443, SC22-430 (63), (DRB-F2-60-1-2) – B-1-B-B-B, Pool9A-4-4-1-1-1). Inbred lines (CML312, CML445, Gibe-1-158-1-1-1-1, CML395, and 124-b (113)) had intermediate response to the disease. Overall, inbred lines such as CML202, 30H83-7-1, ILOO’E-1-9-1, CML312, CML395 CML445 and 142-1-e were selected with better agronomic performance and resistance to leaf blight for breeding. Twenty selected elite parental inbred lines were genotyped with 20 polymorphic SSR markers. The genotypes used were clustered into five groups consistent with the known pedigrees. The greatest genetic distance was identified between the clusters of lines CML-202 and Gibe-1-91. Eighteen selected inbred lines were crossed using the factorial mating scheme and 81 hybrids developed to determine combining ability effects and heterosis. Inbred lines with high GCA effect (CML 202, CML395, 124-b (113), ILOO’E-1-9 and CML 197) were selected as best combiners for hybrid development. Additionally five high yielding novel single cross hybrids with grain yield of > 8 t ha-1 and high SCA effects were identified such as CML395 X CML442, DE-78-Z-126-3-2-2-1-1 X CML442, ILOO’E-1-9-1-1-1-1-1 X CML312, X1264DW-1-2-2-2-2 X CML464 and SC22 X Gibe-1-91-1-1-1-1. These experimental hybrids are recommended for direct production or as hybrid testers for hybrid development. Genotype x environment interaction (GEI) effects of 81 newly developed and three check maize hybrids were evaluated across 10 locations in the mid-altitude sub-humid agro-ecologies of Ethiopia. The AMMI-3 and GGE biplot models were used to determine stability. Hybrids such as G68, G39, G37, G77, G34 and G2 were identified as the most stable and high yielding at favorable environments such as Bako, Jima, Arsi Negelle and Pawe in Ethiopia. The genotype and genotype by environment interaction (GGE) biplot clustered the 10 environments into three unique mega-environments. Environment I included Bako, Jima, Asossa, Ambo, Finote Selam, Haramaya and Pawe while environment II represented by Arsi-Negelle and environment III Areka and Hawassa. In general, the study identified valuable maize inbred lines with high combining ability for breeding and novel single cross hybrids for large-scale production or as testers for hybrid development at the mid-altitude, sub-humid agro-ecologies of Ethiopia or similar environments in sub-Saharan Africa. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Maize production in Africa is constrained by abiotic and biotic stresses. Breeders need to have information on the nature of combining ability of parents, their traits and performance in hybrid combination. This requires careful determination of genetic variability of parents, and studying associations between grain yield and adaptive traits to breed superior cultivars which are better able to withstand such stresses. Therefore, this study was aimed at selecting parental testers with best combining ability in hybrid combination with recombinant inbred lines (RILs); and studying the correlation between grain yield and its components in eastern and western South Africa. It was also aimed at determining genetic variation and associations among adaptive traits in hybrids involving RILs. The final objectives of the study were to determine cultivar superiority of testcrosses involving RILs, and to select the best cultivars within and across four different environments. The 42 RILs were crossed to 9 Zimbabwean tropical testers resulting in 1009 hybrids with sufficient seed for planting in trials. From these a sample of 87 hybrids with adequate seed were selected and planted at four sites for combining ability analysis. The hybrids were evaluated at four sites in two regions; western region (Potchefstroom research station) and eastern region (Cedara, Ukulinga and Dundee research stations), during 2011/12 season. The experiments were laid out as augmented alpha lattice design. Trials were managed in accordance with production culture for each region. All quantitative data was subjected to GenStat and SAS statistical softwares. The results from combining ability study indicated that the line general combining ability (GCA) effects played a non-significant role (p > 0.05) in determining grain yield, grain moisture and anthesis date, while they were significant (p ≤ 0.05) for the other traits such as ear prolificacy. The tester main effects were significant for all the traits except ear prolificacy and plant height. Results also revealed that all the traits were controlled by both additive and non-additive genes, where additive gene action had the most contribution to the traits. The non-additive gene action played a minor role suggesting the total GCA effects attributed to both lines and testers predominantly higher over the specific combining ability (SCA) for all traits. In general the additive effects were preponderant over the non-additive gene effects. One cross (L114 x T12) had a significant and positive SCA effect for grain yield. The correlation between grain yield and secondary traits (number of ears per plant, grain moisture content, ear height, plant height, ear position and anthesis date) suggested that indirect selection can be employed to enhance grain yield by breeding for these particular adaptive traits. Path analysis showed that plant height had the highest direct and indirect effect on grain yield indicating its importance among other secondary traits for grain yield enhancement. Phenotypic coefficient of variation (PCV) was higher than genotypic coefficient of variation (GCV) for all the studied traits across all the four environments. All the traits displayed high heritability at Potchefstroom except anthesis date which was highly heritable at Ukulinga. Cedara was the second best site for heritability of all the traits except for the number of ears per plant. The genetic advance for grain yield was the highest at Cedara followed by Potchefstroom, Dundee and Ukulinga. The hybrids exhibited different patterns of variation and distribution for all the traits. This indicated that selection strategies to exploit GCA should be emphasised. Association studies among grain yield and secondary traits such as ear length, number of ears per plant, plant height, anthesis date, silking date and ear leaf area revealed that there were significant phenotypic correlations between grain yield and secondary traits, and among the secondary traits. Ear length had the highest direct effect on grain yield at Ukulinga; number of ears per plant had the highest direct effect on grain yield at Cedara and Potchefstroom; whereas plant height had the highest direct effect on grain yield at Dundee. Grain yield was least affected by indirect factors at all the sites except Ukulinga, where anthesis date had the highest indirect effect on grain yield through silking date followed by plant height through leaf area. The study reveals that there is significant variation among the hybrids for mean performance, indicating that there is opportunity for selection. Overall the findings suggest that direct selection would be appropriate to enhance grain yield. Path analysis revealed that plant height had the highest direct and indirect effects on grain yield, indicating that plant height can be further exploited as the main trait in future breeding programmes for grain yield increment. Hybrid 10MAK10-1/N3 was the best hybrid at Ukulinga in terms of grain yield, relative yield and economic traits. Whereas hybrid T17/L83 was the best hybrid at Cedara in terms of grain yield and relative yield; however, T11/L102 was selected as the most elite hybrid with respect to grain yield, relative yield and economic traits. Hybrid T3/L48 was identified as thebest hybrid at Dundee with respect to grain yield, relative yield and prolificacy. At Potchefstroom the standard check PAN6611 was identified as the best hybrid in terms of grain yield and relative yield followed by developmental hybrid T1/L28; however, developmental hybrid T1/L28 was the best in terms of earliness, prolificacy and ear aspect. Stability coefficients and cultivar superiority index across the sites revealed that four developmental hybrids were identified as best hybrids and they performed better than the standard check. These hybrids will be recommended for further testing in advanced trials. With respect to cultivar superiority, the desired hybrids are required to combine high grain yield with economic and adaptive traits such as high ear prolificacy, low grain moisture, and low ear aspect score (desired) for them to adapt to production environments in South Africa. There was significant variation among the top 25 yielding hybrids. At least 5 hybrids combined high grain yield with the desired complimentary adaptive traits such as quick moisture dry down, prolificacy and ear aspect. The results showed that there is variation in the performance of high yielding genotypes within all the sites, and that agronomically superior cultivars can be identified. The study shows that there is significant variation among the RILs since they interacted differently with the 9 tropical testers. Even among the top 25 selections of RILs in each environment there was still variation for combinations of the desired traits. Significant associations among grain yield and other economic and adaptive traits were observed with implications for breeding strategy. Above all the significant variation gives large score for future breeding of new unique lines. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Maize (Zea mays L.) supports millions of livelihoods in sub-Saharan Africa (SSA) in terms of food and feed. Production of the crop is however limited by several factors, among these, maize streak virus (MSV) disease. Although extensively studied, MSV remains a serious problem in SSA due to several challenges in breeding MSV resistant maize varieties. These include integration of MSV resistant germplasm from different backgrounds, reliance on a few resistant sources, and genotype x environment interactions. This study was designed to assess the breeding potential of several MSV resistant lines in hybrid combinations. Understanding architecture of genetic divergence and background of these genotypes would greatly aid in breeding high yielding and stable MSV resistant hybrids. Experiments were conducted during 2010 to 2012 seasons in Kenya. Diallel crosses and SSR markers were used to characterize MSV resistant maize inbred lines from three programs of CIMMYT, KARI and IITA. In general, this study revealed that MSV is still an important problem in Kenya with high incidence and severity levels in the farmers’ fields. The levels of MSV resistance in locally grown hybrids needs to be improved. Farmers challenged breeders to develop new hybrids that combine early maturing, high yield potential and MSV resistance. The study was successful in identifying the best eight inbred lines for use in breeding new maize hybrids with MSV resistance. The nature of gene effects was established for the first time, in particular the role of epistasis and G x E in conditioning MSV resistance in hybrids. Results indicate serious implications for previous models that ignored epistasis in studying MSV resistance in maize. The inbreds Z419, S558, CML509 and Osu23i, displayed high levels of epistasis for MSV resistance. Unless strong sources of MSV resistance, such as MUL114 and CML509, are used, breeding resistant hybrids will require parents that carry dominant resistance genes. The additive-dominance model was adequate to explain northern leaf blight (NLB) resistance in hybrids, indicating fewer complications in breeding NLB resistant hybrids. The study also reveals that SSR genetic distance data can be used to predict hybrid performance, especially when the correct set of markers is used. Many previous studies have not found any significant relationship between genetic distance and heterosis, due to large G x E and use of a wrong set of markers. The diallel analysis and SSR data established the important heterotic groups, which will be exploited for efficient development of MSV resistant maize hybrids. These strategies will be recommended to programs that emphasize MSV resistance in maize hybrids. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.