The seeds of Trichilia dregeana, Trichilia emetica, Podocarpus henkelii and Syzygium cuminii display the characteristics typical of recalcitrant seeds. It is the phenomena of ongoing metabolic activity and desiccation sensitivity that render them unsuitable for storage by the conventional methods used for orthodox seeds. Investigations on the storage responses of 'sub-imbibed' (partially dried) and fully hydrated seeds of all four species were carried out to study the effects of partial drying on viability and subsequent storage lifespan; i.e. to assess whether 'sub-imbibed' storage is feasible for these species. The outcome of this investigation was proposed to contribute to the resolution of the argument that storing recalcitrant seeds at lowered water contents might extend their longevity; i.e. storage at a relatively high water content but below the fully hydrated level, might prevent germination but would not be sufficient to be injurious to the seed. Seeds of T. dregeana, T. emetica, P. henkelii and S. cuminii were dried to various target moisture contents (which were determined for each species in the initial drying experiment) and then subjected to storage for 3-22 weeks at 6, 16 and 25°C (in sealed containers). In parallel, seeds of each species were stored at the shedding water content. The seeds were periodically removed for sampling, and assessed for water content, germination, respiration, electrolyte leakage and microscopical features. Storage temperature appeared to affect viability of seeds of T. emetica and T. dregeana which displayed characteristics of chilling sensitivity. Storage at 6°C was detrimental (when compared with seeds stored under the same conditions at 16 and 25°C), but regardless of whether the seeds were undried or partially dried prior to storage. The seeds of P. henkelii did not demonstrate chilling sensitivity, the viability not being compromised at 6°C compared with those seeds stored at 16 and 25°C. Syzygium cuminii seeds were not subject to storage at 6°C because previous work indicated that they would be chilling-sensitive. Storage of 'sub-imbibed' seeds of T. dregeana, T. emetica, P. henkelii and Syzygium cuminii does not to confer any benefit over seeds stored in the fully hydrated state; rather it appears to be deleterious to seed survival during storage. This was apparent from the assessment of viability, electrolyte leakage and respiration. Vigour and viability of the 'sub-imbibed' seeds of all species declined more rapidly than the fully hydrated seeds. The only exception was P. henkelii seeds stored at 25°C, the fully hydrated seeds showed no survival after 11 weeks in storage, while 88% of the 'sub-imbibed' seeds survived this period. These results were, however, attributed to the proliferation of fungi on the fully hydrated seeds at 25°C. Although ultrastructural observations were made only on the T. emetica seeds, it was apparent that the cells from the 'sub-imbibed' seeds (after storage at 16 and 25°C) showed extensive degradation, with the intra-cellular components being largely unrecognisable. The cells from the seeds stored in the fully hydrated condition at 16 and 25°C maintained integrity and appeared metabolically active. In keeping with the suggestion that T. emetica seeds are chilling sensitive, the ultrastructure of the cells from both the 'sub-imbibed' and fully hydrated seeds showed deteriorative changes. All the results of the present study indicated that storage in the 'sub-imbibed' state is deleterious to seed survival. It is apparent that the removal of water, however small a proportion, accelerates seed deterioration during storage. Thus 'sub-imbibed' storage has no practical application for the storage of recalcitrant seeds. / Thesis (M.Sc)-University of KwaZulu-Natal, 2007.

The objective of this study was to develop and implement an advanced generation breeding programme at the Institute for Commercial Forestry Research (ICFR) to manage and integrate the many and disjunct breeding and production populations of Eucalyptus nitens established by various entities over the past 30 years at multiple sites in South Africa. To develop such a breeding strategy, a good understanding of the population genetics, and the underlying assumptions made by tree breeders about the species, was needed. Eucalyptus nitens is an important forestry species grown for pulp and paper production in the temperate, summer rainfall regions of South Africa. A tree improvement programme has been ongoing at the ICFR for three decades. The measurement and statistical analysis of data from eight F1 trials established during the 1980s and 1990s have enabled characterisation of the ICFR’s breeding population. Provenance testing showed that the more northerly New South Wales (Australia) Eucalyptus nitens provenances of Barren Mountain and Barrington Tops are distinctly better suited to growth in South Africa than the southern New South Wales provenances and the Victorian provenances, Penny Saddle and Bendoc. Generally, the species was not badly affected by Coniothyrium canker. High Type B genetic correlations for all sites pairs, except one comparison, ranged from 0.75 to 0.99 for diameter at breast height at 76 to 113 months, indicating very little, or no, genotype by environment interaction for diameter at breast height for the genotypes tested in the F1 generation. Narrow sense heritability estimates ranged from 0.01 to 0.34, indicating that the species provides a breeding opportunity for improvement of diameter growth. High genetic correlations of greater than 0.90 between diameter measurements at 52 to 62 months after establishment and diameter measurements at 94 or 113 months were found, indicating that selections can be made reliably at five or six years. Diameter measurements at both 60 months and full rotation (94 to 113 months) were highly correlated with the final height measurements in these trial series (rg > 0.71 and > 0.83, respectively). Predicted genetic gains for the F2 over the F1 generation were highest in the trials at Goedehoop and Arthur’s Seat, with predicted increases in diameter at breast height of 3.07 cm (17.1%) and 3.17 cm (20.7%), respectively, at full rotation. Genetic improvement in the species has been slower than anticipated due to delayed and infrequent flowering and seed production. Three genetic gain trials were established, firstly, to quantify the gains that have been made in the first generation of improvement in the breeding programme; and secondly, to establish whether a number of seed source and orchard variables influence the performance of the progeny. These variables were: the number of flowering trees in the seed orchard, year of seed collection, seed orchard origin and composition of seed orchard seed bulks. Diameter at breast height and tree height were measured in the trials at between 87 and 97 months after establishment, and timber volumes and survival were calculated. Improved seed orchard bulks performed significantly better (p < 0.01) than unimproved controls in the field trials, and genetic gains ranging from 23.2 to 164.8 m3ha-1 were observed over the unimproved commercial seed. There were significant differences (p < 0.01) in progeny growth between the levels of flowering, with higher levels of flowering (R 40 %) producing substantially greater progeny growth than lower flowering levels (S 20 %). The seed orchard origin had no effect on progeny growth in this trial series. This suggests that seed collected from any of the four seed orchards tested will produce trees with significant improvement in growth. Various scenarios investigating a range of assumptions were developed and used to predict genetic gain in the F2 populations. These were compared with realised gains achieved in the genetic gain trials. The family nested within provenance scenarios proved to be closer to realised gain than the family across provenance predictions. Two scenarios were used for family nested within provenance: Firstly, actual flowering for family nested within provenance; and secondly, estimated flowering after a 30% roguing of poor families. For both scenarios, a coefficient of relationship of 0.33 predicted gains closest to the realised gains. Indications were that the effects were additive, and that very little or no heterosis had occurred. The statistical information suggested that outcrossing in the seed orchards was > 80%. This study provides an objective and quantitative assessment of the underlying assumptions used for estimating genetic parameters, and predicting gain in this population of Eucalyptus nitens. At the same time that genetic gain trials were established, F2 trials were planted, using seedlots collected from F1 seed orchards. Analysis of the two F2 trials showed that realised gains for diameter at breast height at 87 months were close to the predicted values and ranged from 1.02 cm to 1.90 cm. Two exceptions were the sites at Helvetia and Babanango, where gains were under- and over-predicted, respectively. Realised heritability estimates, which are related directly to the realised gain and the actual selection intensities used in the seed orchards, reflected this trend. Estimation of breeding values allowed for selection of elite individuals in top families. Both grand-maternal provenance origin and F1 maternal effects were significant in the F2 trials. A Type B genetic correlation of 0.61 for diameter at 87 months indicated the possible presence of genotype by environment interactions for the two F2 sites. A low narrow sense heritability estimate of 0.06 for diameter at breast height at 87 months at one F2 site indicated that more emphasis should be placed on family information rather than individual information at this site. A heritability estimate of 0.17 for diameter at breast height at 87 months at the second site, however, indicated that further improvement is possible in this population of Eucalyptus nitens. Modelling of predicted genetic gain using various breeding strategy scenarios can be a useful tool in assisting with the decision on which strategy or management plan will deliver the most genetic gains per unit time. Such modelling, using the parameters established in the first part of the study, played an important role in developing the advanced generation breeding strategy for Eucalyptus nitens. In addition, the modelling exercise highlighted various management options which could be used to increase gains in the existing production populations or orchards. Indications are that additional roguing of 1) existing Clonal Seed Orchards based on results of F2 trials (i.e., backward selection); and 2) F1 Breeding Seed Orchards based on stricter provenance selection, will markedly increase the quality of the seed produced from these orchards within one season. This study also highlighted the importance of shortening the breeding cycle in Eucalyptus nitens, particularly in view of the delays caused by reticent flowering and seed production in the species. The information and understanding gathered from this study led to the development of a proposal for an advanced generation breeding strategy in Eucalyptus nitens. This proposal uses parental reconstruction of open-pollinated progeny to secure pedigree information of forward selections, thus combining the benefits of increased genetic gain with a shortened breeding cycle. Recommendations on the management and adaption of current production populations to increase gains have been made, because establishment and management of improved material in seed orchards to ensure a sustainable supply of improved seed to the South African forestry industry, is a key objective of the ICFR Eucalyptus nitens breeding programme. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Popcorn is increasingly becoming popular as a snack and is consumed widely all over the world. It is a high value crop, with possible multiplier effects like income generation for the under-resourced communities in the second economy. Despite its popularity, developing countries are battling to meet the demand and rely on importing popcorn grain due to challenges which include poor agronomic traits and slow breeding progress. Most of the imported varieties are not adapted to stress-prone local environments, which are prevalent in tropical sub-Saharan Africa. The objective of the study was to evaluate newly developed hybrids and inbred lines for agronomic and popping quality traits with the possibility for commercialization in future. The study aimed at determining variability for popping ability in inbred lines and hybrids, grain yield and its secondary traits, the nature of gene action, relationships among agronomic and popping quality traits, effect of genotype x environment interaction on agronomic traits and popping method x genotype interaction effects. To determine popping ability, 128 inbred lines were evaluated at the University of KwaZulu-Natal, South Africa, in June 2011 using two popping methods, the microwave method and the hot-air method. The popping quality attributes measured were flake volume, popping fold, number of unpopped kernels, kernel size and quality score. Variability among inbred lines was significant (P<0.05) for all traits. Flake volume ranged from 63 cm3 to 850 cm3, popping fold ranged from 2.5 to 34 times the original volume. Kernel size had a significant positive correlation (r= 0.49) with the number of unpopped kernels. There was a significant strong and negative correlation between flake volume and the number of unpopped kernels (r= -0.62), indicating that either of the two traits would be effective for measuring popping ability. Experimental hybrids were then developed from 87 out of the possible 128 inbred lines. Only the inbred lines with sufficient seed were crossed to develop hybrids. Random crosses were generated at Makhathini Research Station during the winter season of 2011. Crosses were made at random among parents that managed to synchronize their flowering dates, resulting in 119 hybrids with sufficient seed for planting in trials. To determine agronomic superiority, the 119 experimental hybrids and the standard check P618 were evaluated at the Cedara Research Station and Ukulinga Research Farm in the Midlands of KwaZulu-Natal during the summer of 2011/2012. The experiments were laid out as 10 x 12 alpha lattice design, with two replications at each site. Standard cultural practices for maize were followed. The data were subjected to analysis of variance and line x tester analysis in Genstat and SAS statistical programmes. Results indicated that hybrids were significantly different for all agronomic traits. Means for grain yield ranged from 1.0 t/ha to 5.2 t/ ha. General combining ability effects were significant for all agronomic traits, suggesting that additive gene effects were governing these traits. Specific combining ability effects were significant for ear length, number of ears per plant and yield indicating, that non-additive gene effects were influential for these traits. Generally, agronomic traits were highly heritable. Grain yield showed significant and positive correlation with ear length, plant height, ear position, shelling percentage and number of ears per plant, indicating that these were the major yield-determining secondary traits which should be enhanced in popcorn. Although site main effects were highly significant for secondary traits, the hybrid x site interaction was not significant. The results therefore indicate that the hybrids were ranked similarly at both sites. The 119 experimental hybrids and the standard check P618 were evaluated for popping quality, using the microwave and the hot-air popping method. There was a significant variability observed among hybrids for popping quality traits. Flake volume across sites and across popping methods ranged from 734 cm3 to 1288 cm3. Popping fold ranged from 14.69 to 25.75 times the original volume. Additive gene action was more prominent than non-additive action for all popping quality traits. The SCA effects were significant for flake volume, popping fold and number of kernels per 10 g. All popping quality traits had high heritability, indicating that selection would be effective to improve popping. Flake volume was negatively correlated to quality score, indicating that popping expansion is reflected on the quality score and a significant negative correlation between flake volume and number of unpopped kernels. There was significant and strong positive correlation between kernel size and number of unpopped kernels. Hybrid x site interaction was only significant for quality score and kernel size. Hybrid x method interaction was not significant, indicating that popping ability was not dependent on the method. Inbred lines showed significant variation for popping quality and therefore have utility for hybrid development. Significant genotypic variation was also observed among hybrids for agronomic and popping quality traits. Additive gene action was predominantly responsible for both agronomic and popping quality traits. Both agronomic and popping quality traits were highly heritable and positive relationships were identified among traits. Overall, the study indicates opportunities for further breeding progress through selection. / Thesis (M.Sc.)-Unversity of KwaZulu-Natal, Pietermaritzburg, 2012

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.

In clonal deployment programmes of plantation species, there is frequently the need to deploy Eucalyptus species and interspecific hybrids as rooted cuttings. However, the rooting ability of a particular species or hybrid is a major, and usually limiting, factor affecting the economics of commercial deployment. There is also significant between-species and between-family variation for this trait. Recently, Eucalyptus longirostrata was crossed with E. grandis in an effort to combine its desirable wood properties, drought tolerance and disease resistance with the latter's vigorous growth. Should progeny with these suitable characteristics be identified, there is the possibility of extending plantations to more marginal areas and increasing the quality and volume from existing plantations. An investigation was undertaken to study the rooting ability of E. grandis x E. longirostrata hybrid cuttings. The plant material was sourced from five families in seedling derived hedges at two nurseries, as well as five families coppiced from an unreplicated progeny trial planted in the midlands of KwaZulu-Natal. Their rooting ability was assessed by determining the percentage of cuttings that developed roots using two different rooting methods. The variation between and within families and clones is presented. The study shows that root strike is under moderate genetic control, with an estimate of broad-sense rooting heritability of 0.197 (S.E. = 0.070). The two nurseries used in this study used different rooting technologies, with cuttings rooted either in media (traditional method) or in air (aeroponically). The aeroponics technology was highly significantly (p<0.0001) superior, in terms of rooting success. Rooting was also highly significantly affected (p<0.0001) by the temperature at the time of cutting. Rooting success of cuttings from seedling-derived parental hedges was similar to cuttings from coppiced stumps. The consequences of the low repeatability of measurements of rooting ability, 0.187 (S.E. 0.067) by clone and 0.340 (S.E. 0.072) by ramet, which was influenced by the response to age of material and nursery conditions, is discussed. This study demonstrated that large improvements in rooting success can be made by the optimization of rooting protocols and selecting for superior genotypes, as long as the performances of genotypes are accurately assessed. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

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 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.

Maize grain contains high levels of phytic acid which chelates iron, zinc and other micronutrients as it passes through the digestive systems of monogastric consumers reducing their bioavailability. Breeding for low phytic acid (LPA) content to improve micronutrient bioavailability is hampered by a tedious and destructive colorimetric method on the grain, low yields compared to the wild-types and reduced seed germination and vigour of LPA mutants. Breeding for LPA therefore should also incorporate breeding for improved germination and vigour in the mutants. Molecular markers to speed up the selection process and studies on gene action and combining ability for germination, vigour and yield parameters of the LPA mutants in combinations with other different maize germplasm will speed up breeding for this trait. The objectives of this study were: to develop a molecular marker linked to the lpa1-1 gene and apply this marker for foreground selection in a backcross breeding programme and to use amplified fragment length polymorphism (AFLP) markers for background selection to recover the recurrent parent genome to speed up the backcrossing process; to study gene action and combining ability for seed germination, vigour and yield from diallel crosses involving LPA mutants, QPM and normal endosperm maize inbred lines by replicated laboratory seed tests ( standard germination test and accelerated aging test) and field evaluations in South Africa and Zimbabwe. A co-dominant single nucleotide polymorphism (SNP) marker which detects the transition base change of C/T nucleotides was developed from the gene sequence to identify the lpa1-1 trait. The 150 bp lpa1-1 SNP marker was validated by forward and reverse DNA sequencing of the parental amplification products which confirmed the C to T base change resulting in the LPA phenotype. The lpa1-1 SNP marker was used for foreground selection in 250 BC(2)F(1) progenies of CM 32 (LPA) x P 16 as the recurrent parent. This SNP marker was used to genotype the lines into homozygous dominant (wild type) and homozygous recessive (LPA) genotypes by their melting profiles and heterozygous genotypes by the normalised difference plots using high resolution melt (HRM) analysis. Seventeen heterozygous and 11 homozygous recessive lines were identified for background selection by fingerprinting with AFLP markers to determine the amount of recurrent parent (P 16) genome present. There were six EcoRI/MseI primer combinations tested with 277 data points scored (84% polymorphism rate). The amount of recurrent parent (P 16) genome recovered ranged from 62% to 92% with 13 lines showing greater than 83% of the recurrent parent genome. The effects of diallel crosses generated between four LPA, three QPM and three normal endosperm maize lines were determined for seed germination and vigour using the standard germination and accelerated aging seed tests under laboratory conditions in accordance with the procedures of the International Seed Testing Association. The specific combining ability (SCA) effects and general combining ability (GCA) effects were significant for the seed germination and vigour traits, indicating that genes with non-additive and additive effects were important in controlling these traits. However, the SCA effects were greater than GCA effects suggesting that genes with non-additive effects were predominant. The LPA parents showed reduced vigour compared to the normal and QPM inbred lines under both conditions, with LPA lines CM 31 and CM 32 showing stress tolerance. There were some combinations involving LPA lines, such as LPA x normal, LPA x QPM and LPA x LPA that retained high vigour and high germination rates under accelerated aging conditions, suggesting that they could be stress-tolerant.. A 10 x 10 diallel involving four LPA, three QPM and three Nm inbred lines was evaluated in replicated trials across six environments. Results show that both additive and non-additive gene effects were significant for resistance to northern corn leaf blight (NCLB), grey leaf spot (GLS) and Phaeosphaeria leaf spot (PLS) diseases. The additive gene effects were predominant for the yield and associated secondary traits such as days to mid-pollen shed (DMP), days to mid-silking (DMS), ear per plant (EPP) and grain moisture content (GMC) and grain yield. The LPA lines were early flowering and had quick grain dry down rate but all showed undesirable negative and significant GCA effects for yield. The yield of the LPA x LPA, LPA x Nm and LPA x QPM group of crosses was lower than the check hybrids by about 32 to 67% showing the need for yield improvement of the LPA combinations. An eight x eight diallel involving two LPA and six normal endosperm lines was evaluated over two seasons in five locations with two replications for grain yield components and foliar diseases. There was significant additive and non-additive gene action for both seed germination and vigour traits with predominance of non-additive gene effects. Both additive and non-additive gene effects were significant for yield and associated traits such as anthesis dates and number of ears per plant. However, the additive gene action was predominant for yield and associated traits. Generally the LPA lines and their combinations showed lower germination and vigour. The LPA line, CM 32 showed stress tolerance under accelerated aging conditions. There were three LPA x Nm crosses that showed improvements to the means of seed germination and vigour and yield traits. Results indicated that there was not any significant correlation between yield and seed germination and between yield and vigour. Yield was, however, significantly and positively correlated with anthesis dates and GMC, indicating that higher yield was associated with longer growing cycles. This study was able to successfully develop and apply the lpa1-1 SNP marker for foreground selection and AFLP markers for background selection in a backcross breeding programme. Problems of low seed germination, seedling vigour and grain yield of LPA lines and their combinations were confirmed. However results also indicated some potential of combining the LPA and QPM traits in a single cultivar. In general, procedures such as reciprocal recurrent selection, that emphasise both GCA and SCA effects would be recommended to improve seed germination, seedling vigour and yield in developing varieties with LPA trait. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

The first objective of this study was to evaluate Eucalyptus urophylla S.T. Blake provenances in terms of their growth, basic wood density and pulp yield properties. The second objective was to determine the genetic and phenotypic associations that may exist between growth, basic wood density and pulp yield. Data of 9022 open-pollinated progenies representing 306 families, collected from 17 provenances, were used to evaluate growth. To evaluate basic wood density and pulp yield, as well as the genetic and phenotypic associations between the three traits, data of 300 open-pollinated progenies representing 30 selected families from 11 provenances were used. Narrow-sense heritabilities for all three traits were estimated from data collected in a single E. urophylla provenance/progeny trial planted in northern KwaZulu-Natal. The results showed that significant provenance effects for growth, basic wood density and pulp yield were observed. Heritability was found to be strong for basic wood density (h2 = 0.51) and moderate to weak for volume growth and pulp yield (h2 = 0.17 and h2 = 0.11, respectively). This suggests that big genetic gains can be achieved for basic wood density. Although the heritability estimates for volume growth and pulp yield were weaker, this still allows for tree breeders to make significant genetic gains through accurate selection from this E. urophylla breeding population. Genetic and phenotypic associations between the three traits were estimated from data collected in the same trial. The genetic correlation between volume growth and pulp yield was positive and moderately strong (rA = 0.66). The genetic correlation estimate between volume growth and basic wood density was found to be negative but weak (rA = -0.08). The genetic association between pulp yield and basic wood density was found to be positive but weak (rA = 0.17). Correlation estimates between volume growth and basic wood density, as well as between pulp yield and basic wood density produced standard errors greater than the correlation itself (s.e. = ± 0.32 and ± 0.22, respectively). These high standard errors, coupled with weak genetic correlations, suggest that these correlation estimates are non-significant, but are probably a result of utilizing a small sample size. However, these correlations have a value in making breeding choices, if treated with caution. Key words: Eucalyptus urophylla, provenance, growth, basic wood density, pulp yield, heritability, genetic correlation / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

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.