Seventy-two commercial hybrid grain sorghums, representing 20 commercial sources, were grown full season for grain yield with irrigation water applied as necessary to prevent moisture stress. The test, grown at the University of Arizona Marana Agricultural Center, had grain yields ranging from a high of 6375 lbs/acre down to 3292 lbs/acre.

Seventy-two commercial hybrid grain sorghums representing 17 commercial seed companies were grown full season for grain yield with limited irrigation for medium moisture stress. The test, grown at the University of Arizona Marana Agricultural Center, had grain yields ranging from a high of 5098 lbs/acre down to 2100 lbs/acre.

Seventy-two commercial hybrid grain sorghums representing 17 commercial sources were grown for grain in a late planted, simulated double-crop after barley or wheat harvest. The test, grown at the University of Arizona Marana Agricultural Center, was planted in a pre-irrigated seed bed, but was rainfed thereafter. Grain yields ranged from a high of 3420 lbs/acre down to a low of 1750 lbs/acre.

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Eleven full season hybrid grain sorghums, representing seven commercial sources, were grown on a silty clay soil south of Duncan. The test plots were managed the same as the rest of the field planted to DeKalb 69. Grain yields ranging from 6911 to 4546 pounds per acre were obtained, with DeKalb 69 the top yielder.

Nine medium to medium -late maturing grain sorghum hybrids were compared for yield, percent moisture at harvest, bushel weight, plant height, percent bird damage and standability. The highest yielding entry in the trial was a new hybrid from Northrup King (NK 2656). Its yield of 6185 pounds per acre was 11% higher than the most, commonly grown hybrid in the area.

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.

Sorghum [Sorghum bicolor (L.) Moench] is one of the most important cereal crops grown in arid and semi-arid regions of the world. The North Eastern regions of Ethiopia are known for its high sorghum production and genetic diversity, and proneness to moisture stress. Globally, moisture stress is one of the major sorghum production constraints limiting genetic gain through breeding. Although, the importance of Ethiopia’s sorghum germpalsm has been widely recognized both nationally and internationally, the genetic potential of the germplasm has not yet been fully assessed and exploited in breeding programmes. Therefore, the objectives of this study were: (1) to evaluate sorghum production systems and patterns, major production constraints and cropping mechanisms, varietal diversification, farmers’ criteria for choosing varieties over time and space, and adoption of improved varieties, (2) to assess the agro-morphological and molecular diversity and population structure of lowland sorghum landraces collected from different geographic origins using morphological and SSR markers, (3) to assess the performance of sorghum landraces under moisture stress conditions and identify promising lines, and (4) to determine heterosis and combining ability of lowland sorghum landraces for grain yield, yield components and drought tolerance and to identify suitable parents for future hybrid cultivar development for the North Eastern Ethiopia or similar environments. A survey was conducted in the North Eastern Ethiopia sampling three Administrative Zones, six Districts and 12 Peasant Associations. Data was gathered from a total of 171 farmers and analyzed using SPSS statistical package. The results suggest that the performance of sorghum was generally poor mainly due to moisture stress, pests, diseases, weeds, farmland fragmentation due to demographic pressure, poor soil fertility, and poor performance of the local varieties. The productivity of sorghum was also largely hindered by the use of inherently poor yielding local landraces as farmers were forced to abandon their high yielding, big-headed and late maturing sorghum varieties due to the prevalence of recurrent moisture stress. The survey found that the region is as a rich source of genetic diversity and more than 70 distinct sorghum landraces were identified. The majority of the farmers grew their local landraces, despite the accessibility and availability of many improved sorghum varieties and production packages. Farmers were willing to adopt the improved varieties if they had farmers preferred attributes such as as red seed colour, tall with high biomass yield. To benefit the most from the available improved technologies, farmers have to be part of the breeding process right from the very beginning. Lowland sorghum accessions which exhibited farmer-desired traits were selected from the entire landrace germplasm collection at the national gene bank of Ethiopia. Field evaluations of the selected 278 landraces together with checks were held at Sirinka and Kobo agricultural research stations for 12 qualitative and 10 quantitative traits under stress and non-stress conditions. Two hundrad landraces were selected on the basis of their morphological distinctiveness and drought tolerance, in terms of earliness and yield stability. Molecular level diversity assessment was conducted using 30 SSR markers. Considerable magnitude of variation was observed among landraces between and within geographic origin for most of the traits studied. The morphological variability was also complemented by high molecular markers diversity. Thirty two pure lines were selected for inclusion as parents in the sorghum breeding programme for yield and drought tolerance. The selected lines were then crossed to four cytoplasmic male-sterile lines that had different cytoplasm systems (A1 to A4) using a line x tester mating design scheme. The 32 parents, together with the 128 hybrids and 4 check varieties were evaluated for grain yield, yield components traits and drought tolerance under stress and non-stress environments. Data were analysed using GenStat statistical package following a fixed effects model. Non-additive gene action was predominant in controlling plant height, grain yield, above ground biomass, grain filling duration, 100-seed weight and panicle weight, whereas additive gene action was found more important in controlling days to 50% anthesis and panicle length. Novel landraces with high GCA effects were selected including 214838-A, 242039-B, 75454, 73056-B, and 242050-A which will serve as potential parents for cultivar development. Similarly, the study identified new experimental hybrids i.e. ICSA 749 x 242039-B, ICSA 756 x 242049-B, ICSA 756 x 75454, ICSA 756 x 73059 and ICSA 756 x 214855 with high SCA effects and heterosis for grain yield which will be forwarded for further stability analysis and farmers participatory selections at representative growing environments. In general, the study identified invaluable sorghum germplasm and candidate hybrids useful for further breeding and conservation strategies. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Sorghum (Sorghum bicolor) is the third most important cereal food crop in Uganda. However, the parasitic weed Striga hermonthica severely constraints its production. The use of Striga resistant sorghum varieties may be one of the most feasible ways of managing the Striga problem. A series of studies were carried out with the overall objective to develop new sorghum genotypes that are resistant to Striga and high yielding in Eastern Uganda. Initially, a participatory rural appraisal (PRA) was carried out with the main objectives to study the current constraints faced by farmers in sorghum production and determine their preferences for new sorghum varieties. Secondly, fifty different African sorghum accessions were evaluated to determine phenotypic and genotypic variability for Striga resistance and identify suitable parents to be used in breeding for new Striga resistant and high yielding sorghum genotypes. Thirdly, a genetics study was conducted to determine gene action responsible for Striga resistance and sorghum yield in new sorghum genotypes. Finally, laboratory studies were carried out to identify specific mechanisms of Striga resistance available in new sorghum genotypes and their parents. During the PRA, Striga was identified as the main constraint limiting sorghum production in Eastern Uganda, followed by insect pests. Farmers indicated preference for red gain sorghum with erect and compact heads, a plant height of 1.5m and a maturity period of around three months, as well as Striga resistance and drought tolerance. From farmers’ own assessments, the individual field surveys and soil seed bank analyses that were carried out, the degree of Striga infestation in farmers’ fields was found to be high. Both phenotypic and genotypic factors contributed significantly to the variability observed among the African sorghum accessions with respect to Striga resistance and sorghum crop performance indicating that Striga resistance can be improved through selection. However, techniques that minimise environmental effects need to be employed in order to improve on heritability. The values for genetic coefficient of variation (GCV) and genetic advance (GA) indicated that genetic gain for Striga resistance could be achieved by selection based on area under Striga severity progress curve (AUSVPC), area under Striga number progress curve (AUSNPC) and individual Striga emergence counts. The sorghum accessions SRN39, Brhan, Framida, Gubiye, Wahi, P9407 and N13 were found to be resistant to Striga hermonthica. These accessions consistently showed low AUSNPC, AUSVPC, and individual Striga emergence, Striga vigour and severity indices. These accessions could be used as sources of Striga resistance genes when breeding for Striga resistance in sorghum. In the study to determine gene action responsible for Striga resistance and sorghum yield, significant genetic variation for Striga resistance and sorghum yield parameters was observed among the new sorghum genotypes and their parents. The sorghum parental lines: Brhan, SRN39, Hakika and Sekedo consistently had negative GCA effects for AUSNPC and AUSVPC, while SRN39 and Hakika additionally had negative GCA effects for Striga vigour, indicating that they were effective in transferring Striga resistance into their progeny. The new genotypes: SRS1608, SRS3408, SRS2408, SRS4609, SRS3108, SRS2908, SRS2609, SRS609 and SRS1708 had negative SCA effects for AUSNPC, AUSVPC and Striga vigour meaning that they were resistant to Striga. Sorghum parental lines: Sekedo, Brhan, Framida and Hakika had positive GCA effects for head length, meaning that they increased head length in their crosses. The genotypes: SRS3408, SRS5309, SRS1608 and SRS2908 derived from the above parents had the longest heads compared to other progenies, which were on average, 20% longer than their parents. The genotypes: SRS609, SRS1408, SRS2608 and SRS3408 were the highest grain yielders and yielded 11-51% better than the highest yielding parent (Sekedo) under the non Striga environment. The parental lines; Sekedo, Brhan and Framida had positive GCA effects for grain yield indicating that they could act as sources of genes for grain yield increase. The genotypes; SRS609, SRS4609 and SRS2908 had large positive SCA effects for grain yield. The relative contributions of GCA effects to the observed genotypic variances were 80.5%, 43.3%, 65%, 92.6% and 53.2% for AUSNPC, AUSVPC, Striga vigour, sorghum head length and plant height respectively. This shows that additive gene action was important in controlling Striga resistance, sorghum head length and plant height in the present sorghum populations. Laboratory studies aimed at investigating the specific mechanisms of Striga resistance available in new sorghum genotypes found that two new sorghum genotypes, SRS1608 and SRS1208 expressed both the low germination stimulant character and low haustoria initiation as mechanisms of resistance to S. hermonthica. The sorghum genotypes, SRS2808 and SRS1108, and two fixed lines, Brhan and Hakika expressed only the low germination stimulant character, while the genotypes, SRS608, SRS3408, SRS4109 and SRS2308 expressed only the low haustoria initiation mechanism. The inheritance patterns of the low germination stimulant character in the present sorghum genotypes varied. In some genotypes, it appeared to be controlled by a single gene while in others; it appeared to be controlled by more than one gene. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.