No description available.

No description available.

A comparative study was undertaken of different extraction methods for the isolation of volatile organic compounds from Murraya koenigii (curry leaf plant). The techniques studied included the traditional methods of extraction, namely, Soxhlet and solvent extraction as well as steam distillation. The solvent–free extraction techniques of headspace analysis and headspace solid phase micro-extraction (HS-SPME) were also investigated. In the evaluation of SPME, two different fibre coatings, poly(dimethylsiloxane) and poly(acrylate), were compared. Preliminary work to determine the effect of extraction parameters, such as extraction time, was carried out. The volatile oils in the fresh leaves of Murraya koenigii were isolated by the above-mentioned extraction methods and analysed by gas chromatography-mass spectrometry. The main aroma contributing compounds were identified by comparison of their retention times with those of standards and their mass spectra with those of known compounds contained in the National Institute of Science and Technology Standard Reference Database 1A (NIST 98). The essential oil contained mainly terpenes: monoterpene and sesquiterpene hydrocarbons. The constituents were identified and only the five selected analytes of interest, a-pinene, β-pinene, a-phellandrene, β-caryophyllene and a-caryophyllene were quantified in three of the methods, namely solvent extraction, soxhlet extraction and steam distillation. From the quantitative determination of the compounds of interest, steam distillation favoured the extraction of β-caryophyllene. The solvent and Soxhlet extractions showed no significant differences between the quantities obtained for a- and β- caryophyllene. The steam distillation and Soxhlet methods showed similar quantities of a-caryophyllene extracted. The extraction of the monoterpenes, a-pinene, β-pinene, and a-phellandrene, was favoured by the Soxhlet method of extraction. Quantification was difficult with HS-SPME and headspace analysis. Headspace analysis proved effective in the detection of the very volatile analytes. Headspace-SPME combined with GC-MS was found to be suitable for the identification of both monoterpenes and sesquiterpenes of M. koenigii. From this study, solvent extraction and Soxhlet extraction were found to be superior to the other methods studied for the characterisation and quantitation of the volatile organic compounds in essential oils of Murraya koenigii. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

No description available.

No description available.

Wheat leaf rust, caused by Puccinia triticina Eriks. (= P. recondita Rob. Ex Desmaz. f. sp. tritici), is the most widespread disease of wheat worldwide and causes average annual yield losses of 5 to 25%. The emergence of a new predominant race of leaf rust, TDBG, in the 2004 Canadian virulence survey led to the identification of a second leaf rust resistance gene segregating in the Thatcher-Lr1 near-isogenic differential line, RL6003, which produced an unusual mesothetic infection type. This gene was subsequently isolated in a Thatcher background and temporarily designated as LrCen (Tc-LrCen). A cross was made with a susceptible parent (Tc-LrCen/ Sumai3-lr34) and a doubled haploid (DH) mapping population was generated from the hybrids. Parental lines and 180 double haploid (DH) individuals were phenotyped with race TDBG and a 1:1 ratio was observed in the DH population. Parental lines and 94 DH individuals were genotyped with the Illumina Infinium assay using a custom iSelect 90K wheat SNP array. Two-point linkage between the phenotype and polymorphic SNP markers identified linked markers. A BLAST search of linked SNP sequences was performed against the Wheat Survey Sequence providing a putative chromosomal location of 7AL. Subsequent mapping with microsatellite markers confirmed LrCen was located on the long arm of chromosome 7A flanked by gwm344 (9.5 cM) and cfa2240 (0.6 cM) as well as a group of co-segregating SNPs also at a genetic distance of 0.6 cM. When the SNP sequences were converted to the kompetitive allele specific PCR (KASP) markers they were found to be dominant, making them less useful for marker assisted selection in populations with heterozygotes. LrCen mapped distal to Lr20; the only other Lr gene previously identified on chromosome 7AL. / October 2016

No description available.

Call number: LD2668 .T4 1950 W6 / Master of Science

A Thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg for the Degree of Doctor of Philosophy / Greening is a severe disease of citrus and is a major cause of crop loss in many parts of Africa and Asia.Numerous attempts have been made by various workers to isolate the aetiological agent of the disease and although reports claiming the successful culture of the organism have appeared, the isolations were never fully confirmed. ( Abbreviation abstract ) / AC2017

This thesis presents an investigation into the development of plasmodesmata (PD), which are specialised pores in plant cell walls through which the cytosol and membranes of neighbouring cells are linked. Modification of PD from their initial single-tube (‘simple’) structures to branched (‘complex’) structures is an important part of tissue maturation as it allows cells to restrict the movement of syplasmically mobile molecules including hormones, RNAs and proteins. Conversion of PD from simple to complex is co-ordinated across large populations of cells to produce symplasmic domains, transport barriers, and preferential transport pathways. The development of PD is therefore intrinsic to the wider development and morphogenesis of cells, tissues, and organs. The aim of this project was to investigate the development of PD from simple to complex, particularly during the predictable, large-scale conversion of PD structure that accompanies the leaf transition from sink state to source. To study this I used transgenic plants expressing a GFP-tagged viral protein which accumulates specifically in complex PD, while leaving simple PD unlabelled. The project follows the development of complex PD from the early stages of leaf development to maturity using a range of microscopy techniques. Structured illumination microscopy was used to view labelled PD at super resolution, which gave new structural details about complex PD using a breakthrough technology. Conventional and high-throughput confocal and electron microscopy were used to localise PD within tissues in a broad survey of PD location in leaves to identify patterns of PD development. An imaging chamber was developed that allowed the development of complex PD to be viewed in real time and identified conditions that can trigger structural conversion of PD. Finally, a high-throughput microscopy study was performed to identify how hormones, sugar availability, environmental stresses, defence responses and inhibitors can affect PD development.