Polygalacturonase-inhibiting proteins (PGIPs) are plant proteins believed to playa role in the defence against pathogenic fungi. In this study. it was hypothesized that apple PGIPI could be used to confer enhanced resistance against Verticillium-wilt. a major disease of potato caused by the fungus Verticillillm dahliae. Transgenic lines containing the apple pgip1 gene under control of the enhanced CaMV 35S (e35S) promoter had been generated previously. Stable integration of the transgene into the potato genome was shown by the polymerase chain reaction (PCR) and Southern blot with a DIG¬labelled apple pgip1 fragment as probe. Polygalacturonase (PG)-inhibiting assays (the agarose diffusion assay and reducing sugar assays) were employed to investigate the inhibiting activity of apple PGIP I extracts, prepared from the transgenic potato lines. on the PGs secreted by V. dahliae grown on pectin medium. Inhibition was successful for all but one of the transgenic lines. Active PGIPI was expressed in the leaves of in vitro- and glasshouse grown plants, as well as in roots of in vitro-grown plants. Due to the success of the in vitro inhibition results. it was anticipated that the apple pgip1 transgene would protect the transgenic lines against Verticillium-wilt in a subsequent glasshouse trial. The transgenic lines and untransformed BP I potato control were planted in soil inoculated with V. dahliae microsclerotia and control soil. Assessments of the visual symptoms of yellowing and wilt were made on a scale of 1-5. Colonisation of stem sections was determined by plating onto potato dextrose agar plates. Disease index values were calculated from the symptom and colonisation data. Analysis of variance indicated six lines to be significantly different from the rest when grown in the inoculated soil, but five of them also showed significantly slower senescence symptoms when grown in the control soil. It is proposed that the physiological effect of an extended juvenile phase resulted in the apparent increased disease resistance. This could be caused by transformation or tissue culture¬-induced somaclonal variation of the potato plants. The hypothesis that transformation of the apple pgip1 gene into potato would confer enhanced resistance against Verticillium-wilt was not supported by the data that was obtained. Expression of antifungal genes by pathogen-inducible promoters is a valuable strategy in the development of disease resistant crops of importance. A construct containing the apple pgipl gene under control of the pathogen-inducible gst1 promoter from Arabidopsis thaliana (L.) Heynh was generated. Agrobacterium tumefaciens GV31OI(pMP90RK) was transfonned with the plant transformation vector pCAMBIA2300 containing the gst1 and e35S promoter-pgip1 inserts. A. thaliana was transformed using the floral-dip method, and putative transgenic progeny were selected by kanamycin selection of the seeds. PCR verified the insertion of the transgene into the genomes of T2 and T3 lines. Gene expression from the two promoters was compared by performing PGIP extractions and the agarose diffusion assay. The gst1 promoter was active even without induction by methyl-salicylate. Both constructs led to the expression of active apple PGIP1 against V. dahliae PG in the heterologous plant A. thaliana. / Dissertation (MSc (Plant Biotechnology))--University of Pretoria, 2006. / Plant Science / unrestricted

Since the first report of Verticillium wilt of potato in 1950, the disease has been considered to be of minor importance in South Africa. Between 1995 and 2000, however, Verticillium spp. were isolated from 146 samples of symptomatic potato plant material received from 13 of the 14 potato production areas in the country. Of 93 Verticillium isolates that were obtained, 60% were identified as V. dahliae and 8 % V. nigrescens. V. dahliae was present in nine of the regions and V. nigrescens in seven. Unidentified Verticillium species were isolated from six of the regions. Both V. dahliae and V. nigrescens were pathogenic to potato in vivo, with V. dahliae the more virulent of the two species. Ten South African potato cultivars, eight of which have recently been released, were evaluated over two seasons in a greenhouse for resistance to V. dahliae. The cultivars Aviva, BP1, Bravo, Buffelspoort, Caren, Hoevelder and Ropedi were classified as susceptible to Verticillium wilt, whereas Calibra, Dawn and Devlin were rated as very susceptible. No resistance or tolerance was evident. The efficacy of broccoli volatiles on in vitro mycelial growth of Verticillium dahliae, and the effect of incorporation of fresh and dry broccoli residues on the survival of microsclerotia of V. dahliae and infection of potato, were determined in the laboratory and greenhouse. Volatiles emanating from freshly harvested macerated broccoli leaves were inhibitory to mycelial growth of V. dahliae on medium. Fresh and dry residues incorporated into soil artificially infested with V. dahliae, significantly reduced the viability of microsclerotia of the pathogen and the rate of infection of potato plants. Dry residues were more effective than fresh residues in reducing the viability of sclerotia, but suppression of infection was independent of the state of the residues. / Dissertation (MSc (Plant Pathology))--University of Pretoria, 2005. / Microbiology and Plant Pathology / unrestricted

In common bean (Phaseolus vulgaris), the main seed storage pests are the bruchid beetles. Damage done to the seed by the larvae has a large impact on seed quality and yield. Arcelin (ARC), phytohaemagglutinin (PHA), and α-amylase inhibitor (α-AI) are linked seed storage proteins that form the APA locus on chromosome Pv04 and are associated with resistance. A major breeding objective is to introduce bruchid resistance into common bean from a resistant tepary genotype, G40199, by introgressing the resistant APA locus into susceptible common bean backgrounds. Here we developed a molecular marker that tracks the introgression. A set of PCR primers to the α-amylase inhibitor locus amplified a DNA fragment that showed a 45 base pair insertion in the middle of a lectin Leg_b domain. This enhanced locus characterization and insertion/deletion marker may preclude the need for bruchid resistance screening early in the breeding. / United States. Agency for International Development / United States. Global Hunger and Food Security Initiative (Cooperative Agreement No. EDH-A-00-07-00005-00)

Most breeding programs aim at developing superior germplasm and better cultivars that combine high yield, disease and pest resistance, and end-use quality to satisfy the requirements of the growers as well as industry. A population, consisting of 138 F2-8 recombinant inbred lines (RILs) derived from a cross between ‘Steele-ND’ and ND 735, was evaluated to study the inheritance pattern of the septoria tritici blotch (STB)-resistant genes, agronomic and quality traits. The framework map made of 392 markers, including 28 simple sequence repeat (SSR) markers and 364 DArT markers, spanned a total distance of 1789.3 cM and consisted of 17 linkage groups. The map position of quantitative trait loci (QTL) found in this study coincided with the map position of durable STB resistance genes, Stb1. Thirteen QTL were detected for agronomic and quality traits. More saturation of the current map is needed to explore more QTL for this population.

This study investigates modifications to AWPA Standard E18-06 to develop an above-ground field test for subterranean termites native to the eastern United States. AWPA Standard E18-06 was modified in two stages to progressively increase optimum conditions for subterranean termite feeding. Modification II, which incorporated the use of house bricks and feeder strips with a solid ventilated cover, had an increase in termite attack with less variation between tests. This study also investigates the effects of adding antioxidants, both natural and synthetic, and analogues which lack antioxidant properties, to test wood blocks on feeding by Reticulitermes flavipes Kollar using AWPA Standard E1-09. Antioxidants had feeding deterrence and mortality properties to R. flavipes. Conversely, the non-antioxidant analogues, with the exception of the heterocyclic flavanone, had little effect on R. flavipes. It is concluded that R. flavipes instinctively avoids wood which contains high levels of antioxidants, such as heartwood with phenolic extractives.

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