This study was undertaken to develop a fast and reliable nutrient solution technique to screen grain sorghum genotypes for aluminum (Al) tolerance, and to study the gene system controlling the inheritance of Al tolerance in grain sorghum. Twenty-five sorghum genotypes representing a wide range of environmental adaptation were grown in tanks (120 seedlings/tank, approximately 303.0 ml/seedling) of nutrient solution containing 148 uM liter⁻¹ Al. Relative root lengths (RRL) as well as visual symptoms of injury on roots and leaves were the parameters used in evaluating differential Al response of sorghum genotypes. A highly significant negative correlation coefficient was found between RRL and visual symptoms on roots (r = -0.96). Eleven out of the 25 genotypes behaved as Al tolerant and the remaining behaved as Al sensitive. A half-diallel cross involving three Al-tolerant and three Al-sensitive genotypes as identified through the screening test were used to study the gene system controlling the inheritance of Al tolerance in grain sorghum. The F₁ and parents data were analyzed using both Griffing's and Jinks-Hayman methods of diallel analyses. Highly significant GCA and SCA effects were observed for the Al-tolerance trait. The GCA effects were much more important than SCA effects, with the ratio of GCA:SCA being 9:1. From the Vr, Wr graphs the Al-tolerance trait showed predominantly additive genetic effects with some degree of dominance. The six parents fell into four groups according to the relative level of dominance: (1) highly dominant (AR 3010, CI 182); (2) moderately dominant (NB 9040); (3) moderately recessive (Texas Blackhull); and (4) highly recessive (AR 3001 and AR 3006). The degree of dominance was observed to be partial. F₂ populations screened for Al tolerance showed two distinct classes of tolerance with segregating ratios of tolerant:sensitive seedlings of 3:1. This segregation indicated that the Al-tolerant trait was simply inherited, but a wide range of tolerance for Al observed among the 25 genotypes suggested a more complex gene system. Heritability of Al tolerance was very high. The narrow sense and broad sense heritabilities were 77.69% and 99.54%, respectively. These results suggested that a breeding method emphasizing additive gene effects would be favorable in developing Al-tolerant inbred lines.

Artificially aged and non-aged seeds of 22 grain sorghum (Sorghum bicolor L.) F₁ hybrids and their F₂ and F₃ generations were evaluated for germination salt tolerance. Six of the hybrids, along with their F₂ and F₃ generations, were tested for emergence salt tolerance. Effects of seed production environments on germination salt tolerance were also studied using F₂ generations of 12 sorghum hybrids produced under full-season irrigation, limited irrigation, and double-cropping conditions. Germination tests were conducted in a growth chamber, on trays, while the emergence test was conducted in a greenhouse in flats filled with sand. The experiments were conducted under non-saline and saline conditions in randomized complete block designs. Artificial seed aging resulted in significant reductions in germination percentages under both non-saline and saline environments. The overall mean reduction in germination caused by seed aging was more than twice as much under salinity stress as under the non-stress conditions (48 vs. 17%), indicating differential effects of salinity on different quality seeds. Entries that appeared to be resistant to seed aging also had higher germination percentages under salinity stress. Seed production environment influenced germination performance in both non-saline and saline environments. The overall mean germination percentages of sorghum seeds produced under three different field environments were significantly different from one another. Significant differences were observed in germination and emergence percentages within F₁, F₂, and F₃ generations. Except for the F₁ entries, however, emergence index differences within the F₂ and F₃ generations were not significant. Correlations between germination and emergence percentages in the non-saline and saline treatments were generally nonsignificant. This suggests that germination and emergence responses of sorghum may vary under different salinity levels and different environments.

Call number: LD2668 .T4 1985 D59 / Master of Science

Climate change, shrinking arable land, burgeoning population and malnutrition have made all aspects of crop improvement a critical issue. Of these, nutritional quality of crops is perhaps one of the most important aspects. Most cereals consumed in marginal agro-ecological zones of Africa, for example sorghum and maize are impoverished nutritionally. Given therefore the sole reliance on and the levels of consumption per day of such staples (up to 450 g/day), it is clear that most people cannot obtain the recommended daily allowance (RDA) for many nutrients including fibre, edible oil, protein, vitamins and mineral elements. In this thesis, the development of a sorghum mutant population using gamma irradiation and the subsequent employment of various analytical techniques to unravel multiple mutant traits with a significant positive impact on nutritional enhancement in sorghum is described. Protein analysis revealed a mutant designated SY accumulating (at the time) the highest ever reported amount of free lysine (21.6 g/100g) and other essential amino acids and that these changes were associated with induced protein polymorphisms. Adaptation of proton induced x-ray emission (PIXE) for the spatial profiling of the distribution of 9 elements in sorghum seed tissue allowed for the discovery of mutants with variations in the concentrations and distribution of these elements. The observed changes included enhanced or diminished accumulation of elements in preferential accumulation tissues and entire changes in cellular localisation. The locations within a cell and the quantities of an element are often critical determinants of bioavailability. The accumulation of multiple mutations affecting multiple nutritional traits in individual mutant sorghum clearly indicates the versatility of gamma irradiation induced mutations in addressing multiple nutritional challenges of sorghum. This desirable phenomenon was further demonstrated by electron microscopic analysis of starch granules and protein bodies across the mutants. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed changes in size, shape, ultra-structure and packed cell volumes of seed protein- and starch bodies. Induced mutation had a major effect on the protein body structure which in turn resulted in changes to protein digestibility. High digestibility mutants had a unique dense protein matrix with dark inclusions. However, improved protein quality traits were also associated with floury endosperm texture. Since endosperm texture is an important grain quality attribute and plays a major agronomic role, it is important to ensure that future work focuses on improving grain hardness. The mutants obtained in this study are therefore a valuable germplasm source for sorghum breeding and present real opportunities for addressing nutritional challenges of sorghum. / Ph.D. University of KwaZulu-Natal, Durban 2013.

Thesis (MSc (Genetics. Plant Biotechnology))--University of Stellenbosch, 2007. / Despite numerous attempts involving a variety of target genes, the identity of the key regulatory genes of sucrose metabolism in sugarcane is still illusive. To date, genomic research into sucrose accumulation in sugarcane has focused on genes that are expressed in association with stalk development/maturation, with the aim of identifying key regulatory steps in sucrose metabolism. The identification of possible controlling points, however, is complicated by the polyploid nature of sugarcane. Although these studies have yielded extensive annotated gene lists and correlative data, the identity of key regulatory genes remains elusive. A close relative of sugarcane, Sorghum bicolor, is diploid, has a small genome size and accumulates sucrose in the stalk parenchyma. The main aim of the work presented in this thesis was to use S. bicolor as a model to identify genes that are differentially expressed during sucrose accumulation in the stalk of low and high sucrose genotypes. In the first part of the study, a macroarray protocol for identification of differentially expressed genes during sorghum development was established. Firstly, the macroarray sensitivity of probe-target hybridisation was optimised with increasing amounts of target DNA i.e. 0.005-0.075 pmol. The hybridisation signal intensity increased as expected with increasing amounts of probe until the hybridisation signals reached maximum levels at 0.05 pmol. As a result, to ensure quantitative cDNA detection, probes were arrayed at 0.05 pmol when 1 μg target cDNA was used. Secondly, intra-array and inter-array membrane reproducibility was found to be high. In addition, the protocol was able to detect species of mRNA at the lowest detection limit tested (0.06%) and permits the detection of an eight-fold variation in transcript levels. The conclusion was therefore that the protocol was reproducible, robust and can reliably detect changes in mRNA levels. In the second part of the study, sugar accumulation levels in the immature and maturing internodal tissues of sorghum GH1 and SH2 genotypes were compared during the boot and softdough stages. Sugars (i.e. fructose, glucose and sucrose) accumulated differently in the immature and maturing internodes in both sorghum genotypes during the boot and softdough stages, with sucrose being the dominant sugar in both stages. Based on these differences in sugar accumulation patterns, immature and maturing internodal tissues of sorghum genotypes were compared for differentially expressed genes. A number of genes were found to be significantly differentially expressed during both stages. In order to validate the reliability of the macroarray analysis, fourteen genes were arbitrarily selected for semi-quantitative RT-PCR. Seven genes (50%) revealed a similar pattern of transcript expression, confirming the macroarray results. The other seven genes, however, showed a different expression trend compared with the macroarrays. In this study, ESTs from rice and sugarcane were used for probing sorghum. The probability of cross-hybridisation between the probes and various isoforms of the homologous sorghum sequences is thus high, potentially leading to the identification of false positives. In addition, variation in expression patterns could have been introduced by technical and biological variation. Lastly, to verify that changes in the levels of a transcript are also reflected in changes in enzyme activity, seven candidates were tested for enzyme activity. Only three i.e. soluble acid invertase (SAI), sucrose synthase (SuSy) and alcohol dehydrogenase (ADH), out of these seven genes showed enzyme activity levels reflective of the relative transcript expression. We concluded that changes in transcript levels may or may not immediately lead to similar changes in enzyme activity. In addition, enzyme activity may be controlled at transcriptional and at posttranscriptional levels. In conclusion, sugar accumulation in low (GH1) and high (SH2) sucrose sorghum genotypes is influenced by differences in gene expression. In addition, the power of macroarrays and confirmation with semi-quantitative RT-PCR for identification of differentially expressed genes in sorghum genotypes was demonstrated. Moreover, the transcript and enzyme activity patterns of SAI, SuSy and ADH genes showed expression patterns similar to those of sugarcane during sucrose accumulation. Therefore, using sorghum as a model promises to enhance and refine our understanding of sucrose accumulation in sugarcane.

In the breeding of grain sorghum (Sorghum bicolour L. Moench) towards improved nutrition and agronomic performance, new methodologies are required to increase genetic diversity and lower the inputs required to track and screen breeding populations. Near-infrared calibration models were developed by partial least squares (PLS) and test-set validation on 364 sorghum samples to predict crude protein and moisture content on whole-grain and milled flour samples. Models using milled flour spectra were more accurately predictive than those from whole grain spectra for all constituents (eg. Protein: R2 = 0.986 on flour vs R2 = 0.962 on whole grain). Discriminant calibrations were established to classify grain colour using partial least squares discriminant analysis (PLS-DA) based upon CIE L*a*b* reference values and visual ranking. Preliminary calibrations were developed for quantities of 18 amino acids, fat and apparent metabolisable energy (AME) on 40 samples using cross-validation, highlighting potential for reliable calibration for these parameters in sorghum. An investigation into the potential of 12C6+ heavy-ion beam mutagenesis of sorghum seed was undertaken by treatment at RIKEN Accelerator Research Facility (Saitama, Japan) and subsequent breeding at Ukulinga research farm and analysis at the Department of Plant Pathology, University of KwaZulu-Natal, Pietermaritzburg, South Africa. Dosage rates of 75, 100 and 150 Gy were compared in seven sorghum varieties to establish optimal dose treatments as determined by germination and survival rates, visible morphological changes and field data over two seasons of field trials. Crude protein variation within the M2 generation was analysed to compare dose rate effects. The need for higher dose rates was indicated by few quantified differences between treatments and control although good correlations between protein deviation and treatment dose rate were elucidated. Differences in varietal response suggest a need to optimize dose rate for specific varieties in future endeavours. In addition, all mutagenized populations were screened for crude protein content using near-infrared spectroscopy (NIRS). Significant differences in protein levels and standard deviations were observed between treated self-pollinated M2 generations and untreated control populations. Individual plants displaying significantly different protein levels were isolated. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.