Thesis (MScAgric (Plant Pathology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Maize is the most important cereal crop produced in southern Africa. Maize producers, processors, and consumers in the region, however, are affected by Fusarium ear rot, a disease caused primarily by the fungal pathogen Fusarium verticillioides that reduces grain quality and potentially contaminates the grain with mycotoxins (fumonisin). Due to the threat of fumonisin to human and animal health, and the economic losses associated with reductions in grain quality, strategies aimed at the prevention of Fusarium ear rot and fumonisin contamination are required. These preventative strategies should be focused on protecting the crop prior to harvest, as damage is known to occur in the field before storage. Chapter 1 provides the reader with a broad overview of maize production in southern Africa, the disease Fusarium ear rot caused by F. verticillioides, and the contamination of grain with fumonisins. Potential disease management practices are summarised, and the role of host resistance and its underlying mechanisms emphasised. Finally, the use of plant breeding and resistance elicitors as methods to enhance host resistance in maize towards Fusarium ear rot and fumonisin contamination are discussed in detail. The planting of maize genotypes with enhanced host resistance potentially offers the most efficient method to reduce Fusarium ear rot and mycotoxin contamination. If plant breeding is to be used to enhance resistance, sources of genetic resistance are required. These sources would ideally be in the form of locally adapted maize genotypes, such as inbred lines. In Chapter 2, maize inbred lines used in local breeding programmes, which are adapted to the production conditions in southern Africa, were evaluated as potential sources of resistance to Fusarium ear rot and fumonisin contamination. If inbred lines with good genetic resistance were to be identified they could be used by breeding programmes to develop commercial maize cultivars with resistance to Fusarium ear rot and fumonisin. Activation of resistance responses in normally susceptible maize genotypes using resistance elicitors could provide a novel management strategy for Fusarium ear rot control, as no commercial cultivars with complete resistance to this disease have been identified in southern Africa. Elicitors have previously been found to induce resistance to plant pathogens, mostly in dicotyledonous crops, but the ability of a range of elicitors to reduce Fusarium ear rot and fumonisin contamination in maize has not been investigated. In Chapter 3, a variety of chemical elicitors that induced resistance in other plant-pathogen systems were selected based on the different defence pathways that they stimulate, and evaluated in field and greenhouse trials. Three commercial maize hybrids were included in the trial, conducted at two different field sites, and the elicitors were tested for their ability to reduce Fusarium ear rot and fumonisin contamination of grain, as well as for their effect on yield. These elicitors could be applied in the field as part of an integrated disease management programme, are environmentally friendly, and would be affordable to commercial producers that produce the majority of maize in South Africa.

"April 20th 2003." / Includes bibliographical references (leaves 202-220) / xii, 220 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agricultural Science, 2003

The efficiency of selection in the early generations of a potato breeding programme is examined. A number of unselected potato (Solanum tuberosum L) clones were grown in a glasshouse, from true botanical seed, and thereafter in the field at two locations (a seed site and a ware site) for three consecutive years. At each stage, a number of tuber characteristics were visually assessed and yield plus the yield components were recorded. Four potato breeders visually assessed the produce from each clone after harvesting each years trials and were in good agreement as to which clones would be selected in each environment. Selection for visually assessed characters in both the glasshouse and first clonal year produced a desirable response. However, such selection carried a high cost in terms of losing clones with commercial potential. Selecting clones for yield in the seedling and first clonal year was only marginally more effective than a random reduction in number of genotypes, while selection in the second clonal year appeared to be somewhat more effective as judged by performance in later generations. Comparison of a random sample of clones with ones from the same crosses which had been selected at the seedling and first clonal year stage was at best random, with some suggestion, however, of a negative effect. The causes behind the inefficiency of selection were found to be complex. The inefficiency was ascribed, at least in part, to (i) the inaccuracy of assessment on single plant plots; (ii) the "carry-over" effect of the mother tubers and (iii) selection under a short growing season. Although there was a formally significant interaction between progenies and environments, the rank of the mean of a cross remained relatively consistent over different growing conditions. It was found that the mean and square root of the variance obtained from breeders' preference in any of the environments provided a good basis for prediction of the number of clones in each cross which would exceed (or equal) a given target value. The square root of the variance added increasingly to the accuracy of the prediction as the target value increased but was never a major component in such predictions. When the predictions were used to provide ranking of the crosses, the rank correlations showed good agreement between the different environments and between observed and expected ranks. There was no evidence to suggest that univariate cross prediction for any of the other characters under study would not be effective. A new cultivar is unlikely to be successful simply because of high expression for a single character, but will rather be an all round improvement over cultivars already available. Three methods of multivariate cross prediction were therefore examined namely multivariate probabilities, sum of ranks and the frequency of genotypes in a sample that transgress set target values. The characters total tuber weigh t, mean tuber weight, number of tubers and regularity of tuber shape were examined. It was found that a sample as small as 25 clones provided good predictions (as judged by the observed frequencies in a larger progeny sample examined in various environments). The best estimates were obtained using multivariate probabilities based on the means, within progeny variances,. and the phenotypic correlations between variates. The ranking of crosses according to these multivariate probabilities provided good indications of the number of clones which survived selection in an actual breeding scheme. Thus it is suggested that an empirical examination of a sub-sample of the progeny from a cross could be used to determine the crosses which would have the highest probability of producing improved, potato cultivars. Selection of crosses rather than individual clones has several advantages which would favour such techniques being used in the early generations of a potato breeding programme. Cross prediction based on parental performance also provided an indication of the crosses, .and parents, .which would give the highest frequency of desirable recombinants. These predictions were not as accurate as those derived from examination of a sub-sample of progeny from each cross. But they would allow an earlier, and hence powerful, method of prediction.

The improved dry matter digestibility of the brown midrib (bmr) sorghum cultivars is attributed to constitutive deficiencies of the lignin biosynthesis pathways which results in lower lignin concentrations. The lower lignin concentrations are expressed only in a homozygous recessive genotypes and it is phenotypically identified by a brown to tan vascular coloration present in the mid-rib of the leaf blades. Utilizing this trait increases forage consumption and productivity of both dairy and beef production. There is a need to extend this trait into more forage production systems, including those in Central America where forages constitute a major portion of the ruminants’ diets. To achieve this goal, the bmr12 gene was incorporated via conventional breeding, into 16 lines derived from commonly used Central American sorghum varieties. These experimental lines were tested for agronomic performance during 2010 and 2011 in the Central American region. In addition, grain and biomass composition were estimated using near-infrared reflectance spectroscopy (NIRS) whereas the dry biomass digestibility was evaluated using an in vitro approach. The combined analysis indicated the bmr trait increased in vitro dry matter digestibility and reduced acid detergent lignin and acid detergent fiber levels. This combination results in improved sorghum forage quality. Furthermore, negative traits typically associated with bmr mutants such as plant height reduction, delayed flowering, and lodging problems were not observed and the bmr trait had no effect on grain composition. Additionally, post hoc tests identified CI0947bmr as the best experimental line for dry both biomass and grain yield across multiple environments. Stability analysis, identified CI0947bmr as the most stable genotype for both traits. Finally, the “which-won-where” biplot analysis graphically identified CI0947bmr as the best bmr inbred for Honduras, Guatemala and Nicaragua across several environments.

Soybean [Glycine max (L.) Merrill] is an important source of protein and oil for both nutritional and industrial applications. Increasing seed yield and protein concentration is the main goal of many soybean breeders to meet market demands. Soybean breeders have occasionally succeeded in producing high yielding cultivars with increased protein content using conventional means despite the negative correlation that exists between these two traits. The efficiency of breeding for seed yield and protein concentration improvement in soybean could be increased using marker assisted selection (MAS) breeding strategies to select genotypes containing favorable alleles for faster cultivar development. The objective of this study was to identify quantitative trait loci (QTL) associated with seed yield, and separately, seed protein concentration and then compare phenotypic selection (PHE) and MAS approaches for seed yield and protein concentration improvement. Two hundred and eighty two F5 derived recombinant inbred lines (RILs) were developed from a cross of Essex × Williams 82 and genotyped with 1586 single nucleotide polymorphism (SNP) markers. The population was divided by days to maturity (10 days) into three tests (early, mid and late) each with 94 genotypes, with one genotype overlapping in maturity in the mid and late tests. In 2009, the three tests, parents and checks were grown in a randomized complete block design (RCBD) in: Fayetteville, AR; Harrisburg, IL and, Knoxville, TN replicated three times, and evaluated for seed yield and protein concentration. Data were combined within each test across three locations and analyzed using the MIXED procedure of SAS to determine that there were significant genotypic differences among RILs. Composite interval mapping (CIM) detected nine seed yield and ten protein concentration QTL which may be good candidates for MAS as they were environmentally stable. Selections to compare PHE, and MAS for seed yield and protein concentration provided 8 replicated field tests in four relative maturity groups grown in a RCBD replicated three times in three locations in Tennessee, in 2010. We demonstrated that both MAS and PHE may be used to select quantitative traits; however, more studies are required to optimize MAS for quantitative trait improvement. 

Wholegrains have been linked with significant health benefits such as management of cardiovascular disease, diabetes and some cancers. This study aimed to add value to the grain industry by exploring new nutraceutical targets. This was achieved using bioassay guided fractionation. Wheat extracts including wholegrain, endosperm, pericarp and aleurone from different commercial varieties were investigated for in vitro bioactivity in antioxidant, glycosidic enzyme inhibition, anti-inflammatory, anti-cancer, immune function and cholesterol lowering assays. This study found wheat to have antioxidant activity as measured by oxygen radical absorbance capacity (ORAC) assays with higher values reported for the wheat bran extracts. Amino acid trytophan was identified as the most dominant antioxidant compound in the hard wheat variety durum with a TE value of 24217 ± 3158 µmol/g compound. The unsaturated fatty acids oleic, linoleic and linolenic acids proved to be responsible for the majority of the antioxidant activity in the hard wheat bran H2 with TE values of 2424 ± 274, 5220 ± 523 and 5542 ± 102 µmol/g compound, respectively. Wheat bran and germ but not wholegrain or endosperm displayed α-glucosidase and α-amylase inhibiting properties. Through bioassay guided fractionation, phosphoglycerides, 1,2-linoleoylglycero-3-phosphate and 1-palmitoyl-2-linoleoylglycero-3-phosphate were deemed responsible for the α-glucosidase inhibition. Crude wheat extracts were not cytotoxic to a number of human cancerous cell lines. However, some specific fractions showed selective cytotoxicity to the PC3 human prostate tumour cell line. These fractions contained a number of alkylresorcinols with comparative IC50 values (µg/mL) 5-(2-oxotricosanyl)resorcinol (10.9), trans 5-(14-nonadecenyl)resorcinol (13.7), 5-heptadecylresorcinol (22.5) and trans 5-(16-heneicosyl)resorcinol (42.2) to the known anti-cancer agent Chlorambucil (58.7). In this study, wheat bran extracts have not shown any anti-inflammatory inhibition, estrogen binding inhibition, cholesterol lowering or immune function activity. Wheat bran has proved to be a highly nutritious by-product of the wheat milling industry with a number of protective health effects

Thesis (M.Ag.Sc.) -- Dept. of Agronomy, Waite Agricultural Research Institute, University of Adelaide, 1978).

Thesis (Ph.D.) Department of Agronomy, University of Adelaide, 1981. / Photocopy of typescript.

Thèse--Geneva. / "Thèse no. 1250." Bibliography: p. 163-188.

Pollen grains serve a very important role in the life cycle of flowering plants, in that they are involved in the transmission of inherited characteristicsfrom generation to generation. Because of their small size the study of pollen grains has been necessarily associated with the development of the microscope. Not until the middle of the seventeenth century, when Hooke gave the world the compound microscope, was an instrument available with sufficient power to adequately reveal the shapes of pollen grains. However , two of Hooke's contemporaries, Malpighi and Grew, who used a simple microscope , are generally recognized as the co-founders of pollen grain morphology.