Wheat is the biggest winter cereal crop in South Africa and the second largest cereal to feed the population of South Africa. The population of South Africa grows with approximately one million people a year. Consistent wheat production is necessary for food security and is therefore of extreme agricultural and economic significance. Future production increases depend on the ability to improve, or at least maintain, the rate of increase to feed the population. The study was undertaken to investigate genetic improvement (genetic advance) in wheat by various statistical methods of analysis. This was done to determine the most suitable procedure to evaluate genetic improvement in the three wheat production areas of South Africa, namely the Western Cape province, the Free State province and the irrigation areas. The second objective of this study was to demonstrate the trend of yield and the two quality traits [HLM (hectolitre mass) and protein content] over 16 years (1995-2010) by various statistical techniques. The third objective was to compare the AMMI (additive main effects and multiplicative interaction) and the GGE (genotype plus genotype-by-environment interaction) analyses in assessing genotype-by-environment interaction (GEI) for yield and the two quality traits. The fourth objective was to study the relationship among wheat grain yield and the two quality traits by various statistical techniques. Linear regression (TRET) and various variance component methods were investigated to determine genetic advance. The recommended method of determining genetic advance in this study is TRET. In the Western Cape elite trials TRET predicted a genetic advance of 1% per year and genetic advance estimated at 1% genetic improvement for protein content in the cultivar trials. No significant trend was observed in the elite trials of the Free State with TRET. Yield showed 0.5% and 0.6% per year improvement for the two planting dates of the eastern cultivar trials of Free State. A yield improvement of 0.3% per year improvement for the two planting dates of the central cultivar trials of Free State was determined. A genetic advance for yield of 0.7% per year was found in the warm region of the elite irrigation trials and 9% yield improvement per year for the first planting date of the eastern region of the cultivar irrigation trials. A negative trend was observed for the second planting date of eastern region of both elite and cultivar irrigation trials. 172 The effects of GEI on yield and quality traits were studied by comparing the AMMI and GGE analyses. These methods portrayed similar results. An advantage of these techniques is their complementary nature. Although both models portray GEI in various biplots, the AMMI provides statistical evidence to the visual presentation of the GGE biplots. Pearson product moment correlation matrix provided a linear relationship among the variables studied. Principal component analysis (PCA), cluster analysis (CA) and discriminant analysis (DA) offered auxiliary information on the relationship among the factors (e.g. genotypes, years, localities and/or environments) and the variables. DA was not able to indicate direction of genetic improvement in either of the three production areas in this study.

Wheat (Triticum aestivum) is one of the most important cereal crops worldwide and cultivated in a wide range of environments. The production of wheat, based on consumption and other demands, needs to be increased to meet the annual requirements for its domesticated uses. Wheat productivity is influenced by biotic and abiotic stresses. Therefore, appropriate, efficient and environmentally friendly control measures to lessen such stresses need to be applied. Fungal diseases of wheat, including leaf rust, stripe rust, stem rust, powdery mildew and Fusarium head blight (FHB) can cause yield losses. The diseases result in a reduction in grain yield and affect grain quality negatively. The use of resistant cultivars is an effective, economical and environmentally safe approach to lower fungicide dependence and to reduce production losses due to foliar diseases. In this study, we combined rust and FHB resistance genes and/or quantitative trait loci (QTL) and molecular marker analyses were applied using polymorphic microsatellites (simple sequence repeats, SSR). The aim of the study was to combine five rust resistance genes (against leaf, stem and stripe rust) and five FHB resistance genes/QTL for type I and II resistance into a single wheat genotype with the aid of both marker-assisted and phenotypic selection. Molecular markers used in the study are already being used in commercial breeding programmes in South Africa. The study was divided into two phases. Phase one was aimed at combining rust resistance genes/QTL into a single genotype using parental lines AvocetYrSp, Blade, Kariega and CSLr19-149-299 and to select the best lines based on the number and combination of homozygous genes/QTL present. The genes Sr2, Sr26, Lr19, Lr34/Yr18/Sr57 and QTL QYr.sgi-2B were sourced from parental lines and combined in a double cross breeding scheme followed by several rounds of selfing. Selection was done using marker-assisted selection (MAS). The two best rust resistant lines were selected. Line S16(7.3) contained QYr.sgi-2B.1, Lr34/Yr18/Sr57 and Lr19 in a homozygous state while line S726(3.2) contained Lr34/Yr18/Sr57 and Lr19 in a homozygous and Sr26 in a heterozygous state. Phenotypic screening furthermore indicated the presence of YrSp in line S726(3.2). FHB resistance QTL for the second phase of the project were sourced from Frontana (type I resistance) and CM-82036 (type II resistance). The FHB resistant lines were crossed with the two best rust resistant lines in a double cross breeding scheme and selection was done using molecular markers. The study was conducted over a period of three years. A total of 954 individuals of a double cross population were screened with five markers associated with rust resistance genes/QTL and five markers associated with FHB resistance QTL. The following markers were used to screen for accumulated rust resistance genes/QTL: cssfr5 (Lr34/Yr18/Sr57), Gwm148 and Gwm501 (QYr.sgi-2B.1), STSLr19130 (Lr19) and Sr26#43 (Sr26). The markers DuPw227 (3A), Barc133 (3B), Gwm156, Gwm293 and Barc197.2 (5A), Gwm133 and Gwm644 (6B) and Gwm233 (7A) were used to identify individuals containing FHB resistance QTL. The number of resistance markers in the double cross family ranged between one to nine out of the 10 tested markers. The two best lines, 116.3 and 123.1, contained all markers except the marker linked to the minor FHB QTL on chromosome 7A. All tested lines contained Lr34/Yr18/Sr57 in a homozygous state while all other markers were segregating. The best lines will be self-pollinated for use in future breeding programmes.

Induced mutation was incorporated into the South African sweet potato breeding programme to improve elite cultivars for yield, drought adaptation and nutritional quality. Three cream-fleshed cultivars namely Ndou, Monate and Mokone were selected, propagated in vitro and subjected to gamma ray mutagenesis from a 60Co source at SANBS. Radio-sensitivity tests were done on three node cuttings used as explants to determine optimum dosages for bulk irradiation. Data was subjected to regression analysis and calculated LD50 values were 64 Gy for Ndou, 38 Gy for Monate and 55 Gy for Mokone. Variation observed in lethal dosages highlighted the importance to test each genotype or plant material for sensitivity before mutagenic treatment. Bulk irradiation was done at respective optimum dosages and explants were propagated in vitro up to M1V4 and M2V5 stages to dissolve chimeras and obtain stable mutations. Three mutant populations comprised of 8 207 mutant plants were generated. These mutant plants were screened in the glasshouse for phenotypic/morphological changes visible to the naked eye. Mutant plants with changes in leaf shape, vine colour, fused veins, abaxial vein pigmentation, chlorophyll variegation on leaves and root flesh colour from cream to pale orange/yellow, were observed. After screening, 410 mutant plants (4.99%) with phenotypic changes were identified from the generated mutant populations. Mutant plants/lines derived from the cultivar Ndou were further subjected to vegetative drought and heat tolerance screening in the glasshouse. Two experiments were conducted and these mutant lines were evaluated for drought tolerance and drought and heat tolerance respectively. Thirteen mutant lines with improved drought and heat tolerance, when compared to Ndou, were identified from the first experiment. Further drought screening procedures will be conducted to confirm these results. Field evaluation trials were established to evaluate Ndou mutant lines. These were first evaluated in an initial evaluation trial at Lwamondo using single plants established from seedlings in a non-balanced completely randomised design. Mutant lines with three replicates each were harvested, data was collected on root yield and samples were taken and freeze dried for mineral and total starch content analyses. No mutant line had significantly improved root yields compared to Ndou. Thirteen mutant lines with significantly improved Mn and six mutant lines with significantly improved Mg contents compared to Ndou were identified. Total starch contents were significantly higher in four mutant lines than that of Ndou. Non-significant variations were observed in Zn and Fe contents between mutant lines and the control. Promising mutant lines were further identified and evaluated in a replicated preliminary yield evaluation trial at Towoomba. Top cuttings were used to establish the trial. Data was collected on marketable yield, unmarketable yield, total yield, root-flesh colour and dry mass content. Two mutant lines, M96 and M95, had improved total yields of 33.01 t ha-1 and 30.02 t ha-1 respectively compared to Ndou with 22.96 t ha-1. Dry mass contents were also improved in two mutant lines M47 (30.33%) and M28 (29.38%) compared to the control Ndou (27.00%). Root flesh colour changes were identified phenotypically in M224 and M6 with changes from cream to pale orange/yellow. All mutant lines will be subjected to advanced yield and nutrient evaluations including β- carotene quantification to identify mutant lines with improved yield, drought adaptation and enhanced nutritional contents to address food security and micronutrient deficiency in SA.