Tesis sobre el tema "Maize – Varieties"

Large scale and planned introduction of maize (Zea mays) in southern Africa was accomplished during the last 100 years. Since then, smallholder farmers and breeders have been selecting varieties best adapted to their specific growing conditions. Six studies were conducted to generate information on the current levels of genetic diversity and agronomic performance of both farmer-developed and commercially-bred maize varieties in Zimbabwe, Zambia and Malawi to help in the identification of sources of new alleles for improving yield, especially under the main abiotic stresses that prevail in the region. In the first study, 267 maize landraces were collected from smallholder farmers in different agro-ecological zones of the three countries for conservation and further studies. Passport data and information on why smallholder farmers continue to grow landraces despite the advent of modern varieties were also collected along with the landraces. The second study revealed considerable variation for phenological, morphological and agronomic characters, and inter-relationships among the landraces and their commercial counterparts. A core sample representing most of the diversity in the whole collection of landraces was selected for further detailed analyses. The third study revealed high levels of molecular diversity between landraces originating from different growing environments and between landraces and commercially-bred varieties. The Simple Sequence Repeat (SSR) data also showed that the genetic diversity introduced from the original gene pool from the USA about 100 years ago is still found in both the descendant landraces and commercially-bred varieties. The fourth study showed that in general, commercially-bred varieties outyielded landraces under both abiotic stress and nonstress conditions with some notable exceptions. Landraces were more stable across environments than improved varieties. The most promising landraces for pre-breeding and further investigation were also identified. The clustering patterns formed based on agronomic data were different from SSR markers, but in general the genotype groupings were consistent across the two methods of measuring diversity. In the fifth study, the more recently-bred maize varieties in Zimbabwe showed consistent improvement over older cultivars in grain yield. The apparent yearly rate of yield increase due to genetic improvement was positive under optimum growing conditions, low soil nitrogen levels and drought stress. The sixth study revealed that in general, genetic diversity in Zimbabwean maize has neither significantly decreased nor increased over time, and that the temporal changes observed in this study were more qualitative than quantitative. The results from the six studies confirm the origin of maize in southern Africa and reveals that considerable genetic variation exists in the region which could be used to broaden the sources of diversity for maize improvement under the current agro-ecological conditions in southern Africa.

Public agricultural research has been conducted in Africa for decades and has generated numerous crop technologies, while little is understood on how agricultural research affects the poor and vulnerable groups such as children, and how farmers' perceptions affect their adoption decisions. This dissertation helps fill this gap with three essays on adoption and impacts of improved maize varieties in rural Ethiopia. The first essay estimates poverty impacts. Field-level treatment effects on yield and cost changes with adoption are estimated using instrumental variable techniques, with treatment effect heterogeneity fully accounted for in marginal treatment effect estimation. A backward derivation procedure is then developed within an economic surplus framework to identify the counterfactual income distribution without improved maize varieties. Poverty impacts are estimated by exploiting the differences between the observed and counterfactual income distributions. Improved maize varieties have led to 0.8-1.3 percentage drop in poverty headcount ratio and relative reductions in poverty depth and severity. However, poor producers benefit the least from adoption due to their small land holdings. The second paper assesses the impacts on child nutrition outcomes. The conceptual linkage between maize adoption and child nutrition is first established using an agricultural household model. Instrumental variable (IV) estimation suggests the overall impacts to be positive and significant. Quantile IV regressions further reveal that such impacts are largest among the most severely malnourished. By combining a decomposition procedure with estimates from a system of equations, it is found that the increase in own-produced maize consumption is the major channel such impacts occur. The third paper explores how farmers' perceptions of crop traits affects their willingness to adopt improved maize varieties. Under a random utility framework, a mixed logit procedure is implemented to model farmer's adoption intention, where perceptions of key varietal traits are first identified, and then instrumented using a control function approach to account for potential endogeneity. Perceived yield is found to be the most important trait affecting farmers' adoption intention. Further, yield perceptions among previous adopters appear to be affected by within-village peer effects rather than the real crop performance.
Ph. D.

"Maize is the most important food crop in Mozambique. However, maize production is low and is cyclically impaired due to abiotic stresses such as recurrent droughts (particularly in the arid and semi-arid areas), soil infertility, floods, and cyclones events. Biotic stresses, such as pests and diseases, also affect food production. Altogether, these constraints lead to food insecurity and the need for humanitarian food aid from local and international communities. (...)"
N/A

Thesis (M.Sc. (Agronomy )) --University of Limpopo, 2007
Intercropping is the growing of two or more crops simultaneously on the same field, and it is a common traditional practice among resource-poor farmers throughout the Limpopo Province of South Africa. Field studies were conducted at two locations in the province namely, the University of Limpopo experimental farm at Syferkuil, and a farmer’s field at Dalmada during the 2002/2003 growing season, to determine patterns of nodulation in cowpea and lablab varieties under sole culture and in an intercropping system with maize, variety SNK2147 and also to assess biomass accumulation and grain yielding abilities of the component crops in the system. The experiments were established as a randomized complete block design with three replications at each location. Treatments examined were sole maize, two cowpea cultivars: Bechuana white and Glenda; two lablab cultivars, Rongai and Common. The legumes were intercropped alternately within 90 cm inter-row spacing of maize, thus creating a distance of 45 cm between the maize and the legume rows. Cropping system had no effect on cowpea grain yield at Syferkuil, but at Dalmada cowpea yield was reduced. Maize grain yield was significantly affected by the cropping system at both Syferkuil and Dalmada. At both locations, the yields of all the intercropped maize were lower than those of the sole crop maize. The dry matter production of different cropping systems was generally similar during the different sampling dates.
the National Research Foundation,and the Gauteng Department of Agriculture Conservation and Environment

Collaborative plant breeding (CPB) is an approach to crop improvement incorporating close attention to local biophysical and sociocultural environments and interaction between farmers and plant breeders. CPB may have particular potential for improvement in highly stress-prone environments and for low-resource, traditionally based agricultural communities, situations where more conventional approaches have not been effective. However, CPB will require methodological adjustments or innovations relevant to the smaller scale of its target area and its participatory approach. This study investigated methodologies useful to CPB, working with maize farmers from two communities in the Central Valleys of Oaxaca, Mexico. A method for rapid estimation of broad sense heritability (H) was applied in farmers' maize fields. H estimates for morphophenological traits were compared with narrow sense heritability (h2) from half sib family analysis of five of the same populations and with published estimates. Absolute values of H were larger than h2 from this study and the literature, however trait ranking was the same as in the literature, but differed from h2 rankings from this study. With an understanding of their limitations, these rapid, economical estimations provide useful information for CPB work on-farm, where empirical information is frequently lacking. Collegial interaction based on the knowledge and skills of farmers and breeders will depend upon understanding those in terms relevant to each group. Methods from social and biological sciences were integrated to understand selection and its consequences from farmers' perspectives but based on concepts used by plant breeders. Information was elicited regarding farmers' perceptions of their maize populations, growing environments and expectations for response to selection. Farmers' decisions about varietal repertoires imply assessments of local genetic and environmental variation. Traits of high and low heritability are distinguished, as reflected in expected selection response. Farmers' selection practices were not always effective yet they understood the reasons for this and had no expectations for selection response in some traits given the methods available. Farmers' statements, practices and perceptions regarding selection and the genetic response of their maize populations to their selection indicate selection objectives different than may be typically assumed, suggesting a role for breeder and farmer collaboration.

Kenntnisse zur Blattflächenentwicklung von Silomaissorten während der Vegetationsperiode sind erforderlich, um die Ausreife der Pflanzen charakterisieren und neue Sorte bewerten zu können. Die Blattfläche ist eine Funktion von Blattzahl und Blattfläche und kann den Ertrag und die Futterqualität von Silomais in Abhängigkeit von den Umweltbedingungen in unterschiedlichem Ausmaß variieren. Ein maßgebliches Kriterium für das Erreichen einer guten Futterqualität ist die Prognose des optimalen Erntetermins. In den Jahren 2002 und 2003 wurden zwei Experimente am Standort Berge des Institutes für Pflanzenbauwissenschaften (Landwirtschaftlich-Gärtnerische Fakultät der Humboldt-Universität zu Berlin) durchgeführt, um zu zeigen, wie sich Silomaissorten der Reifegruppen früh und mittelfrüh im Blattflächenindex, in der Blattentwicklung sowie spezifischen Blattfläche unterscheiden und welche Unterschiede zwischen zwei Messmethoden zur Bestimmung des Blattflächenindexes bestehen. Unter Beachtung von Ertrag und Futterqualität haben sich bei limitiertem Wasserangebot unter den gegebenen Standortbedingungen Sorten mit einer geringeren Anzahl von Blattgenerationen (13 bis 16) als geeignet erwiesen. Um Trockenmassegehalte in der Gesamtpflanze im optimalen Bereich von 30 bis 35 % im Erntegut garantieren zu können, sollte Silomais speziell unter trocken-heißen Abreifebedingungen dann geerntet werden, wenn mindestens zwei Blätter unterhalb des Kolbenansatzes noch grün sind.
Knowledge of leaf area development of silage maize varieties during the vegetation period is useful in the characterisation of the maturity conditions of plants and in the evaluation of new varieties. Leaf area, which is a function of leaf number and leaf size may affect yield and quality parameters of silage maize at varying levels, depending on the environmental conditions under which the crops are grown. One of the criteria for obtaining good quality forage is prognosis for optimum harvest time. Two experiments were conducted in 2002 and 2003 at Berge research station, belonging to the Institute of Crop Science (Faculty of Agriculture and Horticulture, Humboldt-University Berlin) with the aim to assess how silage maize varieties of maturity group early and mid early differ in LAI, leaf area development, specific leaf area, what differences exist between the two methods used to measure LAI. Considering yield and forage quality, under the condition of location Berge, with limited water availability, varieties with fewer leaves (13-16) may be suitable. To maintain the whole plant dry matter content within the optimum range (30-35%), especially under drought condition, harvest time must fall within the period when at least a minimum of two leaves below the cob leaf are still green.

Low maize yields in the midst of abundant arable land, favourable climatic conditions, input and financial support programs, plagues smallholder maize farming in Eastern Cape Province. These scenarios have led the province to be a net importer of maize. In essence, low production may signify a mis-match between maize varieties being promoted amongst smallholder farmers and their farming system. Thus, the main objective of the study was to investigate the productivity and profitability of different maize varieties and cropping system under smallholder agriculture in selected villages of the Eastern Cape Province of South Africa as well as, the implications posed on the household food security. The study sought to assess: (i) the productivity of different maize varieties and cropping systems, (ii) the effect of GM maize adoption on food security among smallholder farmers, (iii) the profitability of GM, conventional hybrids and OPV maize varieties produced by farmers under different agro-ecological conditions and (iv) the impact of different maize varieties and cropping systems on food security in the smallholder agriculture. A cross sectional quantitative-based survey study was carried out to obtain information from a total of 650 small holder farmers. The study was conducted in three local municipalities in Oliver Reginald (OR) Tambo District Municipality of the Eastern Cape Province of South Africa. Descriptive statistics, partial factor productivity, gross margin analysis, household food insecurity access score (HFIAS), ordinal logistic and linear regression were the analytical techniques used in establishing correlations among variables. Results obtained from the survey indicated that under mono-cropping system, Genetically Modified (GM) maize variety was highly productive with an average yield of 1.9 t/ha whilst, improved OPV maize variety was productive (with an average yield of 1.6 t/ha) under mixed cropping system. Furthermore, GM maize (GM = -R418.10), and landrace (GM = -R1 140.29) maize varieties had negative gross margins whilst, conventional hybrids (GM = R5 181.21) and improved OPV (GM = R1 457.41) were profitable. There was a significant and negative correlation between use of GM maize variety and reduction of household food insecurity. GM maize varieties, improved OPV, white maize, white as well as yellow GM maize varieties had a significant impact in reducing household food insecurity; whilst using more than one variety of maize (landraces and GMO) positively influenced household food insecurity. In light of these research findings, it is recommended that, there is need to address household food security by growing improved OPVs under a mixed cropping system and GM maize under monocropping system.

Farmer-led seed systems (FSS) provide the backbone for small-scale farmers and many rural communities that use traditional methods of farming to produce seeds that grow and adapt to local conditions. FSS differ from one community and farmer to the next, depending on the methods and practices used to maintain seed varieties. Seed diversity can enhance FSS by improving livelihoods and strengthening farmers' networks, thus contributing to resilient communities. Although nuanced, the dualistic agricultural system in South Africa consists largely of subsistence (small-scale) and commercial (large-scale) farming and includes different crop management systems and post-harvest practices. In South Africa, maize (Zea mays) is a major staple grain crop with a significant role as animal and poultry feed. The North West region is one of the highest white-maize-producing provinces in South Africa. Maize seed systems include both traditional, openpollinated varieties (OPVs) and cultivars such as modern hybrids and genetically modified (GM) seed varieties, including those engineered for specific purposes. The dominant GM maize is that designated for pest resistance using Bacillus thuringienesis (Bt), a soil bacterium which produces a toxin that is fatal to a wide variety of insects such as moths and flies. Many small-scale farmers prefer their own traditional seeds for breeding, planting, selection, selling and consuming. However, FSS based on traditional varieties are threatened by modern cultivars which may be introduced in different ways including through seed exchange, purchasing at shops or by pollination from nearby commercial farms. This study was conducted in the Sespond community of the North West Province. The aim of the study was to understand how small-scale farmers in Sespond maintain traditional maize varieties through selection and storage in a complex agricultural landscape that incorporates both formal and informal seed systems. The formal system represents industrialised farms and companies that work with commercial seed. The informal system represents small-scale farmers who rely on their own seed. Qualitative methods included mapping software which was used to obtain visual agricultural data in and around Sespond. Semi-structured interviews were conducted with 30 small-scale farmers to collect information about their farming practices, including the maize varieties planted. Quantitative methods included collecting 20 maize samples from different farmers for genetic analysis. Agdia® immunostrip tests were used to detect for the presence of Crystal protein (Cry protein) produced by the Bt bacterium, engineered to improve the resistance of maize against insects. The results showed that 13 samples were negative for the protein and seven samples were positive for the protein. A key finding is that small-scale farmers are not able to detect the different maize varieties in their seed systems. This represents a threat for traditional seed varieties in the community as without this knowledge, farmers are not able to adequately manage their production and storage systems. Farmers made use of alternative storage methods such as the mill to reduce seed damage they experienced at home. However, the findings of this research showed that there was an increasing risk of farmers' traditional maize being mixed with GM maize at the mill. Farmers' rights to plant and consume traditional maize were therefore undermined. This study recommends that (a) efforts are made to increase awareness among farmers that help to distinguish transgenes from hybrids and traditional maize varieties; (b) measures are implemented at mills to both improve the transparency about the storage and processing of traditional maize and to separate traditional maize from hybrid and GM maize.

Maize damage has been observed from time to time in many parts of South Africa where registered herbicides were applied. Differential cultivar tolerance to certain herbicides was identified as an important factor in many cases where herbicide selectivity was inadequate. A study was done to investigate the existence of differential tolerance of maize genotypes to selected herbicides. Several maize genotypes were screened for tolerance to selected herbicides, both in the greenhouse and in the field. Maize genotypes demonstrated significant differences in their tolerance to all herbicides. Some genotypes were severely injured by certain herbicides while others were not affected at all by the same herbicide. This suggests that maize genotypes should be screened for tolerance to herbicides in order to reduce crop injury by using only appropriate ones for specific genotypes. Generally, hybrids were more tolerant to herbicides than inbreds, indicating that screening may be most necessary in seed production, where inbreds are used, than in commercial production where only hybrids are used. Tolerance of maize to herbicides was more variable to metazachlor than to other herbicides, and metazachlor also injured more genotypes than other herbicides. This was probably due to differences in herbicide mechanism of action. Shoot or root dry mass reduction of some of the maize genotypes occurred without visual injury symptoms, thus suggesting that visual injury may not reliably indicate susceptibility or tolerance to herbicides. The degree of correspondence of herbicide effects on maize in the greenhouse and the field was determined. Comparison of results from the greenhouse and the field showed that there is positive correlation between herbicide effects in the greenhouse and in the field. There was generally good correspondence of major parameters, such as shoot dry mass and injury symptoms, in the greenhouse and in the field. Similarly these parameters were positively correlated with the grain yield obtained from the field. It appears that shoot dry mass and visual injury symptoms could be good predictors of the yield. This indicates that reliable data could be generated through quicker screening at greenhouse level. A total of four herbicides, metazachlor, dimethenamid, acetochlor and the combination atrazine / metolachlor / terbuthylazine, had significant correlations while only two, flufenacet and acetochlor + atrazine/sulcotrione, had no significant correlations for major parameters with the yield. This indicates that the correlation of data was herbicide-dependent. The influence of temperature on maize tolerance to alachlor, metazachlor and metolachlor was investigated. Results showed that low temperatures reduce the tolerance of maize to these herbicides. This could mean that low temperature may reduce the selectivity of these herbicides. Fluctuating temperature conditions of 10°C at night and 35°C during the day, which are found in some maize producing areas, did not affect maize tolerance to the herbicides. The possibility of improving metazachlor tolerance in maize was also investigated. Evidence provided for possible gene effects on the tolerance of metazachlor indicates that maize tolerance to the herbicide could be improved by crossing tolerant parents. The results suggest that it may be possible to improve metazachlor tolerance by crossing appropriate parent lines with dominant genes for tolerance to metazachlor. Ultrastructural changes in the maize seedling root and shoot cells caused by metazachlor were investigated. In susceptible genotypes root cell nucleoli were found to be abnormally large, empty and more abundant than those in untreated control plants. In susceptible plants the chromatids appeared disorganised in cell nucleoli, and both the nuclear and plasma membranes showed signs of disintegrating. There were more and larger vacuoles in the herbicide-susceptible plants. Leaf cells from the susceptible plants had more empty vacuoles and more chloroplasts with generally disorganised content. The bundle sheath chloroplast membranes were dilated in susceptible plants, and the orientation of the grana was disrupted. In the herbicide-tolerant plants, the ultrastructure was not different from that of all the untreated plants. The established differential tolerance of maize to herbicides necessitates the screening of all genotypes to all registered herbicides in order to recommend specific herbicides for certain maize genotypes. Due to the large number of genotypes that would require screening, techniques that yield reliable data quickly have obvious merit. Pot experiments under controlled conditions, which could be selected to promote herbicide bioactivity, are likely to provide data with which the best possible predictions on the risk of herbicide damage in the field could be made. Based on this requirement, environmental factors that should be considered for greenhouse work are: soil with low adsorptive capacity, soil water content close to the field capacity level, and cool temperatures. When screening for herbicide tolerance, the use of herbicide rates in excess of the recommended rate could obviate the need for special environmental conditions, since all the aforementioned factors basically promote the accumulation of higher than usual amounts of herbicide at the site of action in the plant. Therefore, the use of at least a 2X-herbicide rate in screening experiments is advised.
Thesis (PhD (Plant Production: Weed Science))--University of Pretoria, 2006.
Plant Production and Soil Science
unrestricted

The maize weevil (Sitophilus zeamais Motschulsky) is one of the most destructive storage insect pest of maize (Zea mays L.) in tropical Africa and worldwide, especially when susceptible varieties are grown. Therefore, grain resistance against the maize weevil should be part of a major component of an integrated maize weevil management strategy. The specific objectives of this study were to: i) determine farmers’ perceptions about weevil resistance in maize cultivars; ii) determine the genotypic variation for maize weevil resistance in eastern and southern Africa maize germplasm lines; iii) study the gene action conditioning weevil resistance in the inbred line populations from eastern and southern Africa maize germplasm and to measure their combining ability for yield and weevil resistance; iv) determine the effectiveness of two cycles of modified S1 recurrent selection in improving a tropical maize population “Longe5” for weevil resistance and agronomic superiority and v) evaluate the effectiveness of the “weevil warehouse techniques” compared to the “laboratory bioassay technique” as methods of maize screening against the maize weevil. A participatory rural appraisal (PRA) was conducted in three districts between December 2010 and January 2011, to gather information on the maize weevil pest status in Uganda and farmers’ perceptions about improved maize varieties and the major attributes desired in new maize varieties. Over 95% of farmers knew the maize weevil and its pest status, and were reportedly controlling the maize weevil using wood ashes, red pepper and Cupressus sempervirens. The estimated postharvest weight losses attributed to weevil damage was over 20% within a storage period of four months. The most highly ranked attributes desired in the new maize varieties included high grain yield, tolerance to drought and low nitrogen stresses, resistance to field pests and diseases, good storability and resistance to storage pests. In the search for new sources of weevil resistance, a total of 180 inbred lines from three different geographical areas were screened for weevil resistance using the laboratory bioassay technique. Eight inbred lines (MV21, MV23, MV75, MV102, MV142, MV154, MV157, and MV170) were consistently grouped in the resistant class, and therefore selected as potential donors for weevil resistance in the maize improvement programs. Large significant genetic variations for weevil resistance, and high levels of heritability (89 – 96%) were observed. The results revealed that there was no significant association between maize weevil resistance andgrain yield; suggesting that breeding for maize weevil resistance can be achieved without compromising grain yield. Eight weevil resistant and two susceptible inbred line parents were crossed in a 10 x 10 full diallel mating design and the resulting 45 experimental hybrids and their reciprocal crosses evaluated for grain yield and secondary traits under four environments, and also to determine the gene action regulating their expression. The F1 hybrid seed, F2 full-sib and F2 half-sib grain generated from the 45 experimental hybrids and their reciprocals under two environments in Namulonge, were evaluated for weevil resistance using F1 weevil progeny emergence, median development period (MDP), Dobie’s index of susceptibility (DIS), and parental weevil mortality as susceptibility parameters. The general combing ability (GCA), specific combining ability (SCA), and reciprocal effects were all significant for grain yield, with SCA accounting for over 80% of the hybrid sum of squares. Inbred line parent MV44 exhibited positive significant GCA for grain yield and thus can be utilized in the development of synthetics and hybrids. Hybrids MV21 x MV13, MV154 x MV44, and MV154 x MV102 and all hybrids between parent MV142 and the rest of the parental lines exhibited positive and significant SCA effects. For the weevil resistance parameters, the general combining ability (GCA), specific combining ability (SCA) and reciprocal effects were all significant for F1 weevil progeny emergence, MDP, and DIS in the three seed categories. The results revealed that weevil resistance was governed by additive gene action, non-additive, and maternal effects. Parents MV170 and MV142 were consistently exhibiting weevil resistance in the three seed categories and thus recommended for future breeding strategies. Furthermore, most of the hybrids generated from parental line M142 were noted to exhibit outstanding performance in terms of grain yield and weevil resistance. Another study was conducted to determine the effectiveness of two cycles of modified S1 recurrent selection towards the improvement of weevil resistance in a maize population Longe5. Over 540 selfed ears were selected from the source population (C0) and screened for weevil resistance in the laboratory at Namulonge. Based on weevil resistance characteristics, 162 genotypes were selected from C0 and recombined in an isolated field to generate cycle C1. The same procedure was used for generating cycle C2 from cycle C1, but instead 190 weevil resistant C1 genotypes were selected and recombined to form C2. Seed from cycles C1 and C2, together with that from the source population (C0), was used to plant an evaluation trial in three locations, to compare the performance of the three cycles in terms of grain yield and reaction to the major foliar diseases, and also to produce seed for subsequent screening against weevil ii infestation. A total of 54 seed samples were screened for weevil resistance in a laboratory at Namulonge, in an experiment laid out in a randomized complete block design. A reduction in grain weight loss of 65% was registered in the C2 seed, whereas in C1 seed it was 15%. A similar trend was observed for F1 weevil progeny emergence and grain damage. Grain yield results indicated a yield gain of 19% realized from cycle C2 while a yield gain of 7% was realized from cycle C1. Furthermore, reductions in disease severity of 27%, 10% and 13% were exhibited for Turcicum leaf blight (TLB), grey leaf spot (GLS) and rust disease, respectively in cycle C2. The results indicated that Longe5 can be improved for maize weevil resistance, grain yield, and resistance to foliar diseases through selection. Further recurrent selection cycles would be recommended. The last study was aimed at evaluating the potential of shelled grain and suspended ear options of the weevil warehouse technique in discriminating maize genotypes into different susceptibility classes, based on genotype response to weevil attack. It involved comparing the effectiveness of the two options under the weevil warehouse technique with the laboratory bioassay technique using grain damage and grain weight loss as the maize grain susceptibility parameters. Fourteen maize genotypes were screened using the weevil warehouse and the laboratory bioassay techniques at Namulonge. On grouping the 14 genotypes into different response classes, high levels of consistency were observed in the three screening techniques. Therefore, the two weevil warehouse screening options being faster and effective in discriminating maize cultivars towards weevil attack, they were found to be better than the laboratory bioassay technique. The minimum evaluation period required to discriminate genotypes by the two weevil warehouse options was two months from the onset of the experiment. The maize weevil was noted to be an important storage pest constraining maize production in Uganda. The major weevil control measures included proper postharvest handling procedures and use of indigenous technical knowledge. The results also revealed that host plant resistance could significantly reduce grain damage. It was further revealed that grain resistance against the maize weevil could be enhanced through hybridization and recurrent selection; thus the germplasm identified in the study can provide new sources of maize weevil resistance for commercial deployment and further breeding.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Thesis (M.Sc. Agriculture (Agronomy)) -- University of Limpopo, 2019
Limpopo Province is a semi-arid region prone to drought. Crop yields continue to decline due to low soil fertility and poor cropping systems. Cowpea is nutritionally rich in proteins essential for human consumption and livestock feeding. It fixes N2 which becomes available for the succeeding crop in rotation. For this reason, it is used as a companion crop in cereal-legume intercropping systems. Maize is one of the most important grain crops in South Africa, it serves as the major staple food for many households. Phosphorus is one of the macro-nutrient elements required by crops to produce satisfactory yields. The interactions between different rates of P fertilisation and cowpea-maize strip intercropping have not been studied in detail under rain-fed maize-cowpea strip intercropping in Limpopo Province. Many smallholder farmers in Limpopo Province obtain low yields due to the practice of mixed intercropping. Two season (2014/15 and 2015/16) experiments were laid out in a split-split plot design at Syferkuil farm to determine the performance of cowpea and maize varieties in cowpeamaize strip intercropping at varying P application rates. Treatments consisted of factors namely, P levels (0, 15, 30, 45 kg/ha), cropping system (monocropping and intercropping), maize varieties (WE3127 and ZM1423) and cowpea varieties (PAN311, TVu13464, IT86D-1010 and IT82D-889). Data were collected from growth and yield parameters that included (number of days to flowering, plant height, number of days to physiological maturity, root weight, number of pods per plant, unshelled net pod weight, number of cobs per plant, unshelled net cob weight and grain yield) in order to determine their performance. Results obtained revealed that P application levels significantly influenced most of the measured growth and yield parameters of both crops. PAN311 flowered earliest (49 days) across P levels. Increasing P application hastened the maturity of the varieties of PAN 311 and TVu13464 in both seasons. The P levels of 30 and 45 kg/ha reduced the number of days to maturity as compared to 0 and 15 kg/ha. TVu13464 variety produced more pods per plant (30) than other varieties. PAN311 yielded more grains (2491 kg/ha) than other varieties. Maize varieties performed well between P applications of 30 and 45 kg/ha. WE3127 yielded 3462 kg/ha whereas ZM1423 yielded 3306 kg/ha. Intercropping vi system performed better than monocropping system based on the measured growth and yield parameters. Two promising cowpea varieties (PAN311 and TVu13464) performed well and were selected based on their early maturity, drought tolerance and high yielding. Increasing P application levels increased crop yield. Optimum P levels for cowpea-maize strip intercropping were between 30 and 45 kg/ha. The calculated LER values were greater than one which indicates that intercropping was advantageous in land utilisation. The study showed the importance of P application in improving cowpea yield in cowpeamaize strip intercropping.
National Research Foundation (NRF) and University of Missouri, USA

The importance of maize in sub-Saharan Africa and the potential of quality protein maize (QPM) to alleviate the nutritional gap caused by lack of access to adequate protein rich foods were highlighted. Frustrations from complex inheritance systems of the QPM trait leading to calls for more information on the inheritance and stability of the QPM trait, fear of total loss of the QPM trait due to the recessive nature of the opaque-2 gene to the wild type gene in normal endosperm maize when QPM and normal endosperm maize coexist, lack of information on the nutritional value of contaminated QPM grain, and poor linkages with the smallholder farmers were all cited as drawbacks in the promotion and adoption of QPM. Therefore the objectives of the study were: 1) To solicit the participation of smallholder farmers in the development and setting up of QPM breeding goals, objectives and dissemination strategies; 2) To estimate general combining ability (GCA), specific combining ability (SCA) and reciprocal cross effects on anthesis days, quality traits and grain yield among the publicly available elite QPM inbred lines; 3) To compare experimental QPM hybrids with selected check cultivars, and normal endosperm maize hybrids for grain yield performance and kernel endosperm modification scores; 4) To evaluate QPM hybrids for grain yield and kernel endosperm modification scores in selected sub-Saharan Africa target environments. 5) To determine the level of normal endosperm maize pollen contamination that can occur in quality protein maize without loss of nutritional superiority; 6) To estimate the average levels and the patterns of foreign maize pollen contamination in QPM crops coexisting with normal endosperm maize varieties. The contribution of smallholder farmers in setting breeding goals and dissemination strategies for QPM was solicited. One major finding was that the kernel endosperm qualities of landrace “Hickory King” need to be incorporated into new QPM varieties so as to encourage adoption. Farmers preferred getting information on QPM varieties through their local Agricultural Research and Extension (AREX) officers. A diallel study of 36 F1 QPM hybrids and their reciprocals was conducted across seven environments for agronomic traits and three environments for nutritional value traits. There were significant differences for all traits analysed using Griffing Method 3 model 1. General combing ability effects were significant and important in the control of anthesis days, kernel endosperm modification, protein content, tryptophan content, and Quality Index (QI). Specific combining ability effects were highly significant and important in the control of grain yield. There were significant SCA effects for anthesis days and QI but the proportions were lesser than the corresponding GCA effects in both traits. Kernel endosperm modification had significant GCA effects and nonsignificant SCA effects. Reciprocal-cross differences were significant for anthesis days, tryptophan content and QI. Nonmaternal effects were significant for tryptophan content whilst both maternal and nonmaternal effects were significant for QI and anthesis days. Nonmaternal effects were relatively more important than maternal effects in all the cases where there were significant reciprocal-cross differences. The cross with the highest SCA effects for grain yield was CZL03016/CML144. The most desirable cross with the lowest anthesis days was CZL03016/CML144 whilst the most desirable inbred line with the lowest anthesis GCA effects was CZL03016. The inbred line with the most desirable GCA effects for protein content, tryptophan content and QI was CML264Q. Inbred line CML264Q crossed to CZL03016 had significant SCA effects for QI. The most desirable GCA effects for kernel endosperm modification were associated with inbred line CZL03016 followed by CZL01006. Maternal effects for both tryptophan content and QI were associated with inbred line CML264Q. Genotype by environment interaction effects across all the seven environments were significant for grain yield and kernel endosperm modification. Check hybrids performed better than experimental hybrids for grain yield but were not different for kernel endosperm modification. The normal endosperm maize hybrids were significantly better for both grain yield and kernel endosperm modification. However, in all the comparisons the best check or normal endosperm maize hybrid was not significantly better than the best experimental or QPM hybrid, respectively. The most desirable score for kernel endosperm modification was from the cross of CZL01006 to CZL03016 though not significantly different from the check hybrid with the best score. AMMI1 was the best model for kernel endosperm modification scores and AMMI2 was suitable for grain yield. Both environments and hybrids were diverse. Grain yield of most hybrids was not stable with specific adaptation to environments. The most stable hybrid with no specific adaptation was CML176/CML181f with a mean yield of 6.51t ha-1. The putative nutritional superiority of normal endosperm maize pollen contaminated QPM as measured by the QI depended on the environmental conditions. The moisture stressed environment (CIMMYT Harare) had a lower QI value (0.858) and a lower tolerance to pollen contamination of 15.3% whereas the grain produced under near to optimum growing conditions (ART farm) had a higher QI value (0.915) and a higher tolerance to pollen contamination of 31.9% before total loss of nutritional superiority. Thus contaminated QPM grain had nutritional superiority up to a certain point before total loss of nutritional superiority. Geostatistical analysis was used to determine the levels and patterns of pollen contamination that occur when QPM and normal endosperm maize crops coexist under conditions minimising both temporal and geographical isolation to the lowest possible levels for the two independent crops. Higher pollen contamination levels were restricted mostly to the sections of the QPM crop proximal to the rows of normal endosperm maize crop, with the central parts of the QPM crops experiencing relatively low levels of contamination. For the four experiments (QCS200711, QCS200712, QCS200721 and QCS200722) in which the thresholds to nutritional superiority were determined, 87.9%, 94.8%, 62.2% and 65.6% of the crop areas passed for superior QPM grain, respectively. Estimates for average contamination levels of homogenous mixtures of grain from each of the nine experiments were below 20% contamination. The contamination levels were far less than previously thought. “Hickory King” kernel quality attributes were important in breeding QPM varieties for the smallholder farmers. Parents of the 72 hybrids were diverse for the agronomic characters studied and three of the experimental hybrids were found to be adapted and comparable to the check varieties. Quality protein maize tolerance to foreign pollen contamination without loss in nutritional superiority depended on growing conditions. The coexistence of QPM and normal endosperm maize without total loss of QPM nutritional superiority was feasible.
Thesis (PhD.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Thesis (M. Sc. Agriculture (Agronomy)) -- University of Limpopo, 2019
Pigeonpea (Cajanus cajan (L) Millsp.) is an important grain legume crop in tropical and subtropical countries, where it provides a cheap source of protein. Smallholder farmers in Limpopo Province cultivate landraces of pigeonpea, which are characterised with late maturity, low grain yield and being sensitive to photoperiod. To increase the productivity of the cropping system involving pigeonpea, several earlymedium maturity varieties have been introduced. However, performance of the varieties has not been tested in strip intercropping in Limpopo Province. Farmers plant these landraces by using mixed intercropping without definite row arrangement. This practice does not optimise plant density; it hinders farm inputs application and is characterised producing low yields. Therefore, the inclusion of early maturing varieties of pigeonpea in an intercrop will enable farmers to select the best variety for planting in future and thus enhance their output as well as their productivity. The objectives of this study were to assess the agronomic performance of five pigeonpea varieties in pigeonpea-maize strip intercropping, to determine the effect of strip intercropping on maize yield and establish the effect of location and season variations on the performance of both component crops under the intercropping system. Experiments were conducted at the University of Limpopo Experimental Farm (UL Farm) and Ga-Thaba village during the 2015/16 and 2016/17 season. Five improved early-medium maturing pigeonpea varieties (ICEAP 001284, ICEAP 00604, ICEAP 87091, ICEAP 00661 and ICEAP 01101-2) from ICRISAT were evaluated under strip intercropping with maize cultivar PAN 6479. The varieties were selected as earlymedium maturing varieties from previous pigeonpea trials. The trials were laid in a split plot design. The main plot comprised cropping systems (intercrop and monocrop), while the subplot comprised the varieties with three replications. Data collected on pigeonpea were number of days to 50% flowering and 90% maturity number of primary branches; plant height (cm); number of pods per plant; pod length (cm); number of seed per pod; hundred seed weight (g); and grain yield (kg ha-1), whereas on maize, number of days to 50% tasselling and silking; plant height (cm); cob length (cm); cob per plant; grain yields (kg ha-1); and stover (kg ha-1) were recorded. LER was calculated to determine intercropping productivity. Data analysis was done using Statistic 10.0; and Least Significance Difference (LSD) was used to separate the means that showed significant differences at an alpha level of 0.05. The results revealed significant differences in nearly all pigeonpea variables expect (pod length, number of seed per pod and hundred seed weight). Variables that showed significant differences in maize were plant height, cob length, grain yields and stover. Number of days to 50% flowering and 90% physiological maturity differed significantly (P ≤ 0.05) among varieties at the UL Farm and Ga-Thaba. Varieties (ICEAP 001284 and ICEAP 00604) exhibited the shortest number of days to 50% flowering and 90% maturity in both locations during both seasons. The interaction between variety x season (V x S) showed significant (P ≤ 0.05) differences in pigeonpea grain yield. The top yielders during 2015/16 at the UL Farm were ICEAP 01101-2 (1555 kg ha-1) and ICEAP 001284 (1280 kg ha-1), while during the 2016/17 season, they were ICEAP 001284 (937 kg ha-1) and ICEAP 01101-2 (912 kg ha-1). High yielder at Ga-Thaba during the 2016/17 season were ICEAP 001284 and ICEAP 01101-2 with grain yields of 671 kg ha-1 and 627 kg ha-1, respectively. Furthermore, varieties that obtained high yields during the 2015/16 season were ICEAP 001284 (504 kg ha-1) and ICEAP 00604 (541 kg ha-1). Most of the varieties during both seasons at the UL Farm and Ga-Thaba yielded more than 500 kg ha-1 under strip intercropping as compared to mixed intercropping, which obtained yields averages of below 400 kg ha-1. The highest maize grain yields of 1450 kg ha-1 were recorded during 2015/16 as compared to 958 kg ha1 during the 2016/17 season at the UL Farm. The calculated total Land Equivalent Ratio (LER) for the two crops in both locations gave positive and higher than 1 values, which suggests a favourable grain yield advantage for maize-pigeonpea strip intercrop over mixed intercropping. Key words: Cajanus cajan, maize, cropping system, maturity, grain yields, land equivalent ratio

Thesis (MSc. Agriculture (Agronomy)) -- University of Limpopo, 2019
The traditional practice of farmers in Limpopo Province is to mixed and broadcast crops at planting without definite row arrangement. This practice hinders farm input application and results in low crop yields. Strip intercropping, where crops are planted with definite row arrangement, has the advantage of reducing inter-species competition, optimise plant population and increasing crop yield. This study aimed at improving cowpea-maize cropping systems using strip intercropping. The experiment was conducted at University of Limpopo farm and Ga-Thaba village. Five cowpea varieties (Glenda (check)), IT86K-499-35, IT82E-16, IT86D -1010, TVu-13464 and maize (PAN 6479) were evaluated using randomised complete block design with three replications. Data collected were days to flowering, days to maturity, plant height, canopy width, peduncle length, pod length, number of pods/plant, 100 seed weight, grain yield, fodder weight and land equivalent ratio was also determined. Data were analysed using the Statistix 9.0. The results revealed that in both locations TVu 13464 flowered early (50 days) respectively. At University of Limpopo farm TVu 13464, IT82E-16 and IT86D-1010 matured early (89, 88 and 91 days). At University of Limpopo farm, IT82E-16 had high cowpea grain yield (2230 kg/ha) under monocropping and also produced high grain yield of 1373 kg/ha during 2016/17 season. At Ga-Thaba, IT86D-1010 produced high cowpea grain yield of 1085 kg/ha under monocropping and during 2015/16 (660 kg/ha) while IT86K-499-35 also produced high grain yield of 915 kg/ha during 2016/17. The varieties showed yield stability depending on different locations. At University of Limpopo farm, strip intercropping achieved high maize grain yield of 3961 kg/ha during 2016/17. At Ga-Thaba, strip intercropping produced high maize grain yield 747 and 1024 kg/ha during 2015/16 and 2016/17, respectively. Monocropping produced low maize grain yield during 2015/16 with a mean of 425 kg/ha and mixed intercropping had mean of 499 kg/ha during 2016/17. The calculated LER for two crops over two seasons under strip intercropping ranged from 1.25 and 2.14, whereas under mixed intercropping, it ranged between 0.73 and 1.05 over two seasons at University of Limpopo farm. TVu 13464, IT82E-16 and IT86D-1010 are promising varieties for strip intercropping in low rainfall areas because of their early maturity and high grain yield. The calculated LER for two crops over two seasons xx under strip intercropping ranged from 1.62 and 2.98, whereas under mixed intercropping, it ranged between 0.76 and 1.67 in both seasons at Ga-Thaba.
National Research Foundation (NRF) and Water Research Commission (WRC)

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.

There are few maize varieties that are drought tolerant in semi-arid eastern Kenya and farmer perceptions of drought tolerant maize cultivars have not been studied in this region. Farmers in this region use maize landraces that have not been studied for their potential future hybridization. The main objectives of this study were therefore to: (i) study farmer perceptions of drought and preference for maize varieties, (ii) improve drought tolerance in maize populations in the semi-arid eastern Kenya using S1 family recurrent selection, and (iii) classify maize landraces according to their heterotic patterns. A participatory rural appraisal (PRA) was conducted in Machakos and Makueni districts in semi-arid eastern Kenya. A total of 175 farmers were involved in focus group discussions. An open ended questionnaire and a checklist were used to guide the farmers during the discussion sessions. Scoring and ranking techniques were used to assess farmers’ preferences of maize varieties and constraints to maize production. The farmers grew maize as their major crop followed by beans. Nearly 60% of the farmers grew local maize landraces, whose seed they recycled from season to season; 40% grew improved varieties, but mainly composites rather than hybrids. The key farmers’ criteria for choosing a maize variety in order of importance were drought tolerance, early maturity, high yield, and disease resistance. The major constraints to maize production were drought, lack of technical know-how, pests, poor soils, and inadequate seed supply. Maize traits preferred by farmers in a drought tolerant variety included high yield, recovery after a dry spell and the stay green characteristic. Two maize landrace populations MKS and KTU from semi-arid eastern Kenya and three CIMMYT populations V032, ZM423, and ZM523 were subjected to two cycles of S1 progeny recurrent selection for drought tolerance in yield and traits indicative of drought tolerance were measured during flowering and grain filling from February 2005 to September 2007. Evaluation to determine selection gains was done in one trial replicated five times. It was laid out as a 4x4 lattice design and drought was imposed at reproductive stage by withholding irrigation one week before flowering and resumed during grain filling. The trial was repeated under well-watered conditions which served as a control experiment. After two cycles of selection under drought stress conditions, KTU population had a realized gain in yield of 0.2 t ha-1, MKS population 1.2 t ha-1 and ZM423 0.4 t ha-1, whereas in V032 and ZM523, grain yield reduced by 1.1 t ha-1 and 0.6 t ha-1, respectively. Under well watered conditions, the realized gains in grain yield were positive in all the populations except V032, where there was a reduction of 0.1 t ha-1. Selection increased the genetic variability and heritability estimates for yield in S1 lines of MKS and ZM423 populations, but decreased in KTU, V032 and ZM523 populations. The research to identify heterotic patterns was undertaken using ten maize landraces from the semi-arid eastern Kenya, six maize landraces from coastal Kenya, and three maize populations from CIMMYT. These populations were planted at Kiboko Research Farm during the short rains of October-December 2005 and crossed to two population testers, Embu 11 and Embu 12. The evaluation of the test crosses was done during the long rains of March-June 2006. Percentage heterosis for yield ranged from -17.7% to 397.4%, -79.4 to 22.2% for anthesis-silking interval, -23.9% to 29.2% for ear height, -0.1 to 1.1 for ear diameter, -7.1 to 21.2% for ear length and -5.9% to 30.3% for plant height. iii General combining ability (GCA) effects were significant (p=0.05) for all the traits, while specific combining ability (SCA) effects were not significant (p>0.05), implying that variation among these crosses was mainly due to additive rather than nonadditive gene effects. Since SCA was not significant (p>0.05) for yield, maize populations were classified based on percentage heterosis for yield alone. The maize populations therefore, were grouped into three different heterotic groups P, Q and R. Twelve landrace populations and two CIMMYT populations showed heterosis with Embu 11 and no heterosis with Embu 12 were put in one group P. Two landrace populations that showed no heterosis with either tester were put in group Q. Two landrace populations and one CIMMYT population showed heterosis with both testers were put in group R. None of the populations showed heterosis only with Embu 12 and no heterosis with Embu 11. The main constraint to maize production was drought and the farmers preferred their landraces whose seed they recycled season to season. After two cycles of recurrent selection, the landrace populations showed improved progress in yield. Thus, further selection will be beneficial in the populations where genetic variability increased. Therefore, these populations can further be improved per se and released as varieties and/or incorporated into the existing maize germplasm to broaden their genetic base, given that their heterotic patterns have been identified. Considering that farmers recycle seed, breeding should be towards the development of open-pollinated varieties which are drought tolerant.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Maize (Zea mays L.) is the principal crop of Southern Africa but production is threatened by gray leaf spot (Cercospora zea-maydis L.) and phaeosphaeria leaf spot (Phaeosphaeria maydis L.) diseases, drought and the use of unadapted cultivars, among other constraints. There are few studies of gray leaf spot (GLS) and Phaeosphaeria leaf spot (PLS) resistance, drought tolerance, yield stability and maize cultivar preferences in Southern Africa. The objective of this study was to: a) determine farmers’ preferences for cultivars; b) investigate the gene action and heritability for resistance to GLS and PLS, and drought tolerance; and c) evaluate yield stability and its relationship with high yield potential in Southern African maize germplasm. The study was conducted in South Africa and Zimbabwe during 2003 to 2004. A participatory rural appraisal (PRA) established that farmers preferred old hybrids of the 1970s because they had better tolerance to drought stress. Farmers also preferred their local landrace because of its flintier grain and better taste than the hybrids. The major prevailing constraints that influenced farmers’ preferences were lack of appropriate cultivars that fit into the ultra short seasons, drought and low soil fertility. Thus they preferred cultivars that combine high yield potential, early maturity, and drought tolerance in all areas. However, those in relatively wet areas preferred cultivars with tolerance to low soil fertility, and weevil resistance, among other traits. A genetic analysis of 72 hybrids from a North Carolina Design II mating revealed significant differences for GLS and PLS resistance, and drought tolerance. General combining ability (GCA) effects accounted for 86% of genetic variation for GLS and 90% for PLS resistance indicating that additive effects were more important than non-additive gene action in controlling these traits. Some crosses between susceptible and resistant inbreds had high resistance to GLS suggesting the importance of dominance gene action in controlling GLS resistance. Resistance to GLS and PLS was highly heritable (62 to 73%) indicating that resistance could be improved by selection. Also large GCA effects for yield (72%), number of ears per plant (77%), and anthesis-silking interval (ASI) (77%) under drought stress indicated that predominantly additive effects controlled hybrid performance under drought conditions. Although heritability for yield declined from 60% under optimum to 19% under drought conditions, heritability for ASI ranged from 32 to 49% under moisture stress. High heritability for ASI suggested that yield could be improved through selection for short ASI, which is positively correlated with high yield potential under drought stress. The stability analyses of the hybrids over 10 environments indicated that 86% had average stability; 8% had below average stability and were adapted to favourable environments; and 6% displayed above average stability and were specifically adapted to drought stress environments. Grain yield potential and yield stability were positively correlated. In sum, the study indicated that farmers’ preferences would be greatly influenced by the major prevailing constraints. It also identified adequate genetic variation for stress tolerance, yield potential and yield stability in Southern African maize base germplasm, without negative associations among them, suggesting that cultivars combining high yield potential, high stress tolerance and yield stability would be obtainable.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

In Southern Africa and Mozambique, tropical lowland accounts for 22% and 65%, respectively, of area under maize production, but grain yield is compromised by downy mildew disease (DM, which is caused by Peronosclerospora sorghi (Weston and Uppal) Shaw), and lack of appropriate varieties, especially hybrids. Among other factors, productivity can be enhanced by deploying DM resistant hybrids, which are higher yielding than open pollinated varieties. Development of a viable hybrid-breeding programme requires knowledge of genetic effects governing yield and DM resistance in inbreds, and effective germplasm management requires heterotic groups and heterotic patterns to be established. In addition, knowledge of farmer-preferred traits is required. Currently, such information is not available to the hybrid-breeding programme in Mozambique. The objectives of this study were, therefore; i) to identify farmers’ preferred variety traits and major production constraints, ii) to determine combining ability effects of inbred maize S4 lines for grain yield and DM resistance, iii) to determine heterotic groups and heterotic patterns among the elite inbred maize lines, and iv) to investigate gene effects governing resistance to DM in breeding source inbred maize lines from the breeding programme in Mozambique. During 2007/08, 142 households were involved in a survey conducted in three districts representing two maize agro-ecological zones in Mozambique. Formal surveys and informal farmer-participatory methods were employed and data subjected to analysis in the SPSS computer programme. Results indicated that there was a low utilization of improved varieties, especially hybrids, with grain yield estimated at 0.7 t ha-1. Farmers were aware of the major production constraints and could discriminate constraints according to their importance for their respective communities. For the lowland environment, farmers identified downy mildew, drought, and cutworm and stem borer damage as the main constraints. In contrast, for the high altitude environments, they ranked ear rot, seed and fertilizer availability, turcicum leaf blight, grey leaf spot diseases and low soil fertility among the major constraints limiting productivity. The most important variety selection criteria were grain yield, short growth cycle, white and flint grain with stress tolerance to drought, low soil fertility, diseases, and grain weevils. These afore mentioned traits, would be priority for the breeding programmes for the lowland and mid altitude environments in Mozambique. To determine combining ability for downy mildew resistance, heterotic groups and heterotic patterns, two testers (open-pollinated varieties) ZM523 (Z) and Suwan-1 (S), were crossed with 18 lines to generate 36 top crosses for evaluation. Crosses were evaluated at two sites under DM. Preponderance of GCA effects indicated that additive gene effects were more important than non-additive gene effects in governing both grain yield and downy mildew resistance in the new maize lines. Based on specific combining ability (SCA) data, lines for yield were classified into two heterotic groups, S and Z; whereas based on heterosis data, lines were fitted into three heterotic groups (S, Z and SZ). Further heterotic patterns and gene action for yield were determined by subjecting nine inbred lines and the two testers, S and Z, to an 11 x 11 diallel-mating scheme. The diallel crosses, three hybrid checks and the two testers were evaluated in six environments in Mozambique. Results revealed that non-additive gene effects were predominant for yield components. In addition, high levels of heterosis for yield was observed and three heterotic groups identified (Z, S and S/Z), and five exceptional heterotic patterns among the inbred elite maize lines were observed. Topcrosses with yield levels comparable to single cross hybrids were also identified, and these would be advanced in the testing programme with potential for deployment as alternative cheaper and sustainable technology to conventional hybrids for the poor farming communities in Mozambique. To determine gene effects for downy mildew resistance in potential breeding lines, two maize populations were derived from crosses between downy mildew susceptible line LP67, and resistant lines DRAC and Suwan-L1. To generate F2 and backcross progenies (BCP1 and BCP2), F1 progenies were self-pollinated and simultaneously crossed to both inbred parents (P1 and P2). All the six generations (P1, P2, F1, F2, BCP1, and BCP2) of the populations were evaluated at two sites under downy mildew infection. A generation mean analysis was performed in SAS. It was revealed that downy mildew resistance was influenced by genes with additive and dominance effects, plus different types of epistatic effects such as additive x additive, and dominance x dominance. Overall results indicated that genes with predominantly non-additive effects controlled resistance in DRAC, whereas resistance in Suwan-L1 was largely influenced by additive gene effects. These findings have serious implications on the effective use of these downy mildew resistance sources in breeding programmes that aim to generate varieties with downy mildew resistance. Overall, results suggested that inbreeding and selection within heterotic groups, followed by hybridization between inbreds within and across heterotic groups would be effective to generate new hybrids. The breeding programme will consider development of conventional hybrids, such as single crosses and three way crosses, and top crosses. Implications of the findings of the study and recommendations are discussed.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Maize streak virus (MSV) disease, transmitted by leafhoppers (Cicadulina mbila, Naude), and maize downy mildew (DM) disease caused by Peronosclerospora sorghi (Weston and Uppal) Shaw, are major contributing factors to low maize yields in Africa. These two diseases threaten maize production in Mozambique, thus the importance of breeding Mozambican maize varieties that carry resistance to these diseases. Marker-assisted selection (MAS) was employed to pyramid MSV and DM disease resistant genes into a single genetic background through simultaneous selection. Firstly, it was essential to determine the genetic diversity of MSV disease resistance in 25 elite maize inbred lines to aid in the selection of suitable lines for the introgression of the msv1 gene; and subsequently, to introduce the msv1 resistance gene cluster from two inbred lines, CM505 and CML509, which were identified as the ideal parental lines for the introgression of MSV disease resistance into a locally adapted Mozambican inbred line LP23 that had DM background resistance. Pyramiding the resistance genes by the use of simple sequence repeat (SSR) molecular markers to track the MSV gene cluster was investigated in 118 F3 progeny derived from crosses of CML505 x LP23 and CML509 x LP23. High resolution melt (HRM) analysis using the markers umc2228 and bnlg1811 detected 29 MSV resistant lines. At the International Maize and Wheat Improvement Centre (CIMMYT) in Zimbabwe, MSV disease expression of the 118 F3 progeny lines was assessed under artificial inoculation conditions with viruliferous leafhoppers and the effect of the MSV disease on plant height was measured. Thirty-seven family lines exhibited MSV and DM (DM incidence ≤50) disease resistance. Individual plants from a total of 41 progeny lines, that exhibited MSV disease severity ratings of 2.5 or less in both locations within each of the F3 family lines, were selected based on the presence of the msv1 gene based on SSR data, or field DM disease resistance, and were then advanced to the F4 generation to be fixed for use to improve maize hybrids in Mozambique for MSV resistance. Simultaneous trials were run at Chokwe Research Station in Mozambique for MSV and DM disease assessment, under natural and artificial disease infestation, respectively. Thus the MSV and DM genes were effectively pyramided. Lines with both MSV and DM resistance were advanced to the F4 generation and will be fixed for use to improve maize hybrids in Mozambique for MSV and DM resistance, which will have positive implications on food security in Mozambique. This research discusses the results of combined selection with both artificial inoculation and the three selected SSR markers. It was concluded that a conventional maize breeder can successfully use molecular markers to improve selection intensity and maximise genetic gain.
Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Low soil nitrogen (N) and drought impede maize production in the small-scale farming sector in Zambia; and adoption of new cultivars with improved tolerance might enhance production. This study: a) assessed farmer preferences for maize cultivars; b) determined genotype x environment interaction effects among popular maize cultivars under contrasting soil fertility levels and; c) investigated landraces for tolerance to low N and drought using S1 selection. The study was carried out in Zambia from 2004-07. Farmer preference influencing the adoption of maize cultivars was investigated using both formal and informal surveys in Luangwa, Chibombo and Lufwanyama rural districts representing the three agro-ecological regions of Zambia. Focus group discussions and personal interviews were used to collect data on issues that affected maize production in these areas. It has been found that although farmers perceived landraces to be low yielding, they believed that they were superior to improved cultivars for: tolerance to drought; tolerance to low soil fertility; grain palatability; grain storability; and poundability. The need for food security, their inability to apply fertiliser, and their need for drought tolerant cultivars significantly (p ≤ 0.05) influenced farmers in adopting cultivars. The farmers would readily adopt cultivars that address these concerns. The predominant use of certain landraces (76%) reflected their superiority in meeting some of these needs. The performance of nine popular cultivars (three for each of hybrids, OPVs and landraces) under contrasting levels of soil fertility, across six environments (ENVs) in the three agro-eological regions, was evaluated. An ENV was defined as season x location combination. The fertilizer treatments were full fertilization, basal dressing, top dressing and nil fertilization. The cultivars exhibited significant non-crossover type of genotype x fertilisation interaction effects at three ENVs, while the genotype x fertilisation interaction effects, were non-significant at the other three ENVs. The cultivars exhibited dynamic stability by increasing grain yield (GY) when fertilization was increased. Landraces yielded higher than all open pollinated varieties and were generally higher yielding than two hybrids. Based on average rank for GY, the five highest yielding cultivars were MRI724, Gankata, MM603, Kazungula and Pandawe. Superiority of landraces revealed their genetic potential for GY under low soil fertility and they should be used as germplasm in developing cultivars targeting such environments. Ninety-six local landraces were selfed to generate S1 lines (2004/05 season) which were crossed to a tester (2005/06 season). Testcrosses were evaluated under optimal, low N, and drought conditions (2006/07 season). Data on GY, anthesis-silking interval, number of ears per plant, leaf senescence, leaf rolling, tassel size and grain texture were recorded in all the trials during the study period. Testcrosses, their S1 parents and landraces that were superior under low N, drought, optimal conditions and across environments were identified; these should be used to develop varieties targeted to a particular environment. Selection for tolerance to drought also selected for tolerance to low N. Selection for low N tolerance also selected for GY under drought and optimal conditions. Therefore, in selecting for tolerance to abiotic stresses, use of optimal and managed stress environments was effective. The following landraces were superior at 10% selection intensity: LR38, LR84 and LR86 (optimal, low N and drought conditions); LR11, LR35 and LR76 (low N and drought conditions); LR12 (optimal and drought conditions); LR40 and LR93 (low N conditions only); LR79 (drought conditions only) and; LR74 and LR85 (optimal conditions only). These landraces should be used as source germplasm targeting respective environments. Significant (p ≤ 0.05) positive general combining ability effects for GY under both low N and drought conditions were found implying that additive gene action conditioned GY under the abiotic stresses. The heritability for GY under low N (0.38), and drought (0.17) conditions, was low suggesting that selection based on GY alone was not effective. The genetic correlation for GY between optimal, and either low N (rG=0.458), or drought (rG = 0.03) environments, was low (rG < 0.5) suggesting that indirect selection would not be effective either. Therefore, use of secondary traits for selection is discussed. The study established that most farmers depended on local landraces for seed and would adopt low input improved varieties that yield higher than the landraces. Some landraces were found superior to some improved cultivars under contrasting fertilisation regimes. The study also found that landraces had genetic variation for tolerance to low N and drought. Landraces, S1 lines and testcrosses superior under low N, drought, optimal conditions and across environments were selected and they should be used to develop cultivars targeting respective environments. Policy implications of these results are discussed.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

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.

The majority of farmers in Tanzania have not yet adopted modern maize varieties and still cultivate landraces and open pollinated varieties (OPVs) with low production potential and susceptible to diseases like maize streak virus (MSV), grey leaf spot (GLS) and northern corn leaf blight (NLB). The NLB disease is among the major causes of low yield and has been reported in all 21 maize growing regions in Tanzania. Breeding for host plant resistance with high yielding potential and involving the community in the breeding process is expected to address the problem of low yield, NLB disease susceptibility and low rate of F1 hybrid adoption. Therefore, the study was conducted to obtain additional sources of resistance to NLB disease, high yielding cultivars with community acceptable traits adapted to Tanzanian conditions. The main objective was to contribute to increased maize productivity in the western zone of Tanzania. The specific objectives of this study were therefore to : 1) investigate maize production limiting factors for smallholder farmers in western Tanzania, 2) identify farmers and stockist perceptions, opinions and maize variety selection criteria in western Tanzania, 3) establish NLB disease status in farmers’ fields of western Tanzania, 4) determine the genetic relationships among landraces and assess maize landraces as sources of breeding materials, 5) determine the combining ability and heterosis for NLB disease resistance of eleven maize inbred lines adapted to Tanzanian conditions, and 6) determine the gene action and inheritance of resistance to NLB disease in five maize inbred lines adapted to Tanzanian conditions. The study was conducted from 2008-2011 in three diverse environments which represent all the maize growing regions in the country The participatory rural appraisal (PRA) was conducted in three districts to investigate farmers’ and stockists preferred traits for maize selection in western Tanzania, determine maize production constraints facing farmers and assess NLB disease prevalence in the same area. A focus group of 30 farmers was selected in each of the three villages. Transect walks, wealth ranking and historical profiles were used in an informal survey. One hundred and fifty questionnaires were used in a formal survey. The recorded yield was only 1 t haˉ¹. Thirteen major maize production constraints, 13 insect pests and vermin and, 11 diseases were recorded. The NLB disease was reported to be increasing in severity in all farmers’ fields. Farmers’ preferred traits included resistance to abiotic and biotic stresses, early maturity, preferred milling qualities, high storage qualities and high yielding potential. Stockists mentioned 12 preferred maize variety traits which included high yielding, disease and insect pest resistance, heavy grain, large cob size and large grain sizes. Similarity between farmers and stockist variety preference ranking were found to exist. The occurrence and distribution of northern leaf blight (NLB) disease study was conducted to assess the incidence and severity of NLB disease in farmers’ fields in seven districts. The study was conducted for two seasons. In each season, 175 fields with 5600 plants were sampled. There were sixteen varieties grown with wide NLB disease reaction variation. Gembe, a landrace, was among the three observed resistant varieties. The NLB disease has changed its distribution pattern affecting all districts of the western zone. The disease incidence in season two (2009/2010) significantly increased from season one (2008/2009) t= -3.25 (348), P= 0.001. About 30% of both means of blight incidence and severity were recorded in the area. Characterization and screening of maize landraces for northern leaf blight disease resistance was conducted to determine the genetic relationships among landraces, assess maize landraces as sources of NLB disease resistance and assess important agronomic traits for future maize improvement. Ninety breeding materials consisting of 71 landraces and 19 commercial varieties were evaluated. The average yield of landraces under research management was 2.3 t haˉ¹. Landrace TZA 3075 was identified as NLB disease resistant. Yield potential, dent grain texture, white endosperm and husk cover were important agronomic traits observed among landraces. There were high variations in terms of morphology and NLB disease resistance among the landraces. Five principal components contributed to 71.98 % of total variation. Clusters analysis revealed five distinct groups of landraces. Leaves/plant, infested leaves/plant, lesion number, lesion length, lesion width and NLB disease incidence traits highly contributed to variation and grouping of landraces. Combining ability analysis for northern leaf blight disease resistance was conducted to estimate the combining ability for NLB disease resistance of 11 maize inbred lines adapted to Tanzanian conditions, determine maternal effects which are involved in NLB disease resistance in maize germplasm, and determine the heterosis in the F1 hybrids. A full 11 x 11 diallel cross was performed. All top ten experimental hybrids in each of the three sites had negative midparent heterosis for NLB disease severity. The overall mid-parent heterosis means for yield across sites was 152%. The mean sum of squares for GCA was highly significant (P< 0.001) on disease severity indicating additive gene action effects. Mean sum of squares for SCA were highly significant for disease severity and yield implying non-additive gene action effects. The mean squares for reciprocal effects were highly significant on yield and non-maternal sum of squares had significant effect (P<0.05) on yield. The GCA contribution was high for disease severity (91%) and lesion number (85%). Almost, all GCA effects for NLB disease resistance were negative implying contribution to disease resistance. Due to preponderance of the additive gene action, recurrent selection could be used to improve the resistance of inbred lines while the non-additive gene action could be exploited in breeding for disease resistant hybrids. Generation mean analysis of northern leaf blight disease resistance was conducted to determine the mode of gene action involved in the inheritance of resistance to NLB disease in five inbred lines adapted to Tanzania at contrasting environments, estimate heterosis and heritability in five tropical inbred lines. Generation mean analysis was conducted using a six parameter model comprising P1, P2, F1, F2, BCP1 and BCP2 generation progenies. The mean sum of squares for environment, replication with the nested environment, generations, generations x environment interactions were highly significant (P<0.001). The full model of additive, dominance, additive x additive and additive x dominance epistatic effects was highly significant (P<0.001). Nonetheless, the additive gene effects were predominant ranging between 57% and 89% which was matched by large heritability (54%-85%). The average degree of dominance ranged between -0.52 and 0.88 supporting observations of partial dominance. The NLB disease severity showed a continuous distribution in all three sets for F2, BCP1 and BCP2 populations which is an indication of quantitative nature of inheritance and additive gene effects. The mid parent heterosis ranged from -19 to 1%. Therefore, resistance to NLB disease could be improved through selection by exploiting the additive gene effects. The epistatic gene effects would cause less complications because they were negligible (<25%). The client oriented breeding for maize northern leaf blight disease resistance was carried out to perform farmers and stockists assessment on the 110 F1 experimental maize hybrids and compare them with breeders selection criteria. Breeders selection criteria ranked 10 top high yielding experimental hybrids. Farmers developed 14 while stockists developed 13 selection criteria. The most preferred hybrids by farmers were VL 05616 x CML 159, CML 159 x KS03- 0B15-47 and EB04-0A01-304 x CML 442 while stockists preferred VL 05616 x CML 395, EB04-0A01-304 x CML 442 and VL 05616 x CML 159. Two F1 experimental hybrids EB04- 0A01-304 x CML 442 and CML 159 x CML 442 appeared in all top five ranked hybrids by breeders, farmers and stockists. Generally, findings showed that, farmers, stockists and breeders coincide in some selection criteria but also differ in other cases.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

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 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.

Maize is the principal staple food in sub-Saharan Africa (SSA), but production lags behind population growth. The African stem borer, Busseola fusca, Fuller (Lepidoptera, Noctuidae), and the spotted stem borer, Chilo partellus, Swinhoe (Lepidoptera, Crambidae) are serious insect pests of maize in tropical environments. The damage can be managed by breeding stem borer resistant maize varieties but there is limited information that can be used to devise appropriate breeding programs. Therefore breeding investigations were conducted to appraise germplasm screening methods, and to determine combining ability, heterosis and response of maize populations to S1 progeny recurrent selection. The study was conducted in Kenya during 2010 to 2013. The results showed that most of the test genotypes were susceptible to B. fusca and less so to C. partellus, indicating that breeding for B. fusca would be more challenging. Therefore more resources would be required to improve maize germplasm for resistance to B. fusca to broaden the base from which breeders will select suitable lines for breeding. There was a highly significant (r=0.947, p≤ 0.01) correlation between rank selection index in the greenhouse and laboratory. The detached leaf disk bioassay method was effective for screening maize genotypes for resistance to both stem borers. Therefore it will be recommended for use in screening maize genotypes in future studies. The line x tester studies indicated a preponderance of the additive gene effects for borer resistance traits. Specific combining ability effects were significant for resistance traits and grain yield indicating that non-additive effects were also influential. Findings from the breeding investigations will impact positively on both food security and plant breeding capacity. The completed study was successful in identifying new maize inbred lines with resistance to both stem borers. These lines have high utility to maize breeding programmes that emphasise stem borer resistance in tropical environments. For the hybrid-oriented programmes, combining ability and heterotic orientation data for the 66 maize inbred lines will be crucial. In this regard the study was very successful in classifying the lines into three heterotic groups according to single cross testers (CML395/CML444, and CML312/CML442) that are widely used at CIMMYT, and by public breeding programs throughout SSA. Importantly, this was done based on grain yield potential of hybrids under B. fusca and C. partellus infestations in three mega environments. The study demonstrates that S1 progeny recurrent selection is effective for improving stem borer resistance, without compromising yield. There was significant reduction (69%) in maize plant damage by both pests, and yield gains of 25% to 70% were realised in two populations. This represents significant contribution to plant breeding capacity, especially to maize breeding programmes that emphasise stem borer resistance in hybrids.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2014.

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.

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.