Browsing by Author "Burger, P."

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    Confirmation of the effectiveness and genetic positions of disease resistance loci in ‘Kishmish Vatkana’ (Ren1) and ‘Villard Blanc’ (Ren3 and Rpv3)
    (South African Society for Enology and Viticulture, 2018) Veikondis, R.; Burger, P.; Vermeulen, A.; Van Heerden, C. J.; Prins, R.
    This study aimed to validate the effectiveness and to genetically characterise the fungal disease resistance genes of ‘Kishmish Vatkana’ and ‘Villard Blanc’ in South Africa using microsatellite (SSR) markers and a Quantitative Trait Loci (QTL) approach. An F1 ‘Sunred Seedless’ × ‘Kishmish Vatkana’ cross was used to generate a partial linkage map for chromosome 13 known to harbour the Ren1 powdery mildew locus of ‘Kishmish Vatkana’. The effectiveness of this locus was validated, explaining between 44.8% and 57.7% of the observed phenotypic variance. An F1 ‘Villard Blanc’ × ‘G1-6604’ cross was used to generate partial linkage maps for chromosomes 15 and 18, reported to harbour fungal resistance genes of ‘Villard Blanc’. The powdery mildew QTL (Ren3) was validated on chromosome 15 of ‘Villard Blanc’, which explained between 18.9% and 23.9% of the phenotypic variance observed. The downy mildew resistance QTL on chromosome 18 (Rpv3) of ‘Villard Blanc’ was also confirmed, and it explained between 19.1% and 21.2% of the phenotypic variance observed. This molecular information and individual sources of resistance have already been implemented in the marker-assisted selection (MAS) and gene pyramiding efforts of the table grape breeding program of the Agricultural Research Council (ARC) Infruitec-Nietvoorbij.
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    In vitro culture of ovules and embryos from seedless grapes (vitis vinifera L.)
    (South African Society for Enology and Viticulture, 1996) Burger, P.; Goussard, P. G.
    Ovules of stenospermocarpic seedless grapes were cultured under different conditions. The number of embryos was not significantly increased when ovules of Muscat Seedless were cultured on a medium supplemented with the plant growth regulators indole-3-acetic acid and gibberellic acid compared to the basal medium. No correlation was found between the ovule size of Sultanina and the presence of embryos. Comparable percentages of embryos were found in small, medium and large ovules following weekly culture from four to 10 weeks after bloom. Varying results were obtained when ovules of four open-pollinated seedless cultivars were cultured on two basal media with or without activated charcoal. In all four cultivars the highest number of embryos was found at the later culture date. With three cultivars the best results were obtained when ovules were cultured on the medium of Bouquet & Davis (1989), supplemented with activated charcoal. Isolated embryos of Muscat Seedless and Sunred Seedless were cultured under various conditions and it was found that the absence of growth regulators resulted in the highest number of plantlets with normal leaves.
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    Die invloed van die Anglo-Boereoorlog op die siviele bevolking van die distrik Oudtshoorn
    (Stellenbosch : Stellenbosch University, 2007-03) Burger, P.; Venter, C.; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of History.
    ENGLISH ABSTRACT: At the onset of the Anglo-Boer War, the district of Oudtshoorn was characterised by its diverse demographic composition and the prosperity which arose primarily from the trade in ostrich feathers. The district was drawn into the theatre of war relatively late and, when measured against the involvement of certain other districts, for a comparatively shorter period of time. From the outset the war, nevertheless, exerted a significant and far reaching influence on the civilian population of the district of Oudtshoorn. Initially this influence was largely limited to the way in which the community of Oudtshoorn reacted to matters relating directly or indirectly to the war. A powerful and outspoken group whose loyalty to Britain had been fanned by the war to fervent patriotism came to the fore. This group consisted mainly of English-speaking whites residing in the town, although some high profile Dutch Afrikaners and most coloured and black people in the district rallied around this group. On the opposing side there were those – mostly Dutch Afrikaners residing outside the town of Oudtshoorn – who felt a close bond with the burghers of the Boer republics. This group had to find a way in which they could reconcile their loyalty to Britain as subjects of the Commonwealth with their desire to give assistance to the Boer Republics. So, whereas those who were pro-British in the district were often provokingly defiant in their patriotic expression, those who were sympathetic to the Boer cause mostly turned to a modestly reserved, though intense, support of the Republican war effort. This was initially expressed in various forms of humanitarian aid and moral support to the Republicans. Where the loyalist support of the British war effort led to their taking up arms on a large scale, especially during 1901, and serving in various colonial and local corps, so much so that a Coloured Town Guard was even formed, few of the sympathisers rebelled. Notwithstanding this, the residents of the district tried in numerous other ways to assist the Boer Commandos that entered the district in 1901. This aid, which in some cases was simply alleged aid, caused many residents of Oudtshoorn to land on the wrong side of the martial law and they were subsequently severely punished. In this aspect the Military Court which convened twice in Oudtshoorn was a thorn in the flesh of many residents and an eminent author and practitioner of law like C.J. Langenhoven had serious reservations about the administration of justice which took place there. From 1901 martial law was the single most disruptive factor in the everyday way of life of the residents in the Oudtshoorn district. While the proclamation of martial law can be diametrically linked with the arrival of Boer Commandos in the district, the upheaval that one could attribute directly to the commandos is nothing in comparison to the hardship that was suffered as a result of the implementation of martial law. People were affected in all spheres of life. Moreover, the administration of martial law became a breeding ground for both the misuse of power and power struggles in the district. In the midst of the ordeals caused by the war, the economic prospects remained promising especially because of the flourishing trade in ostrich feathers which was hardly affected by the war. Together with the predominantly conciliatory attitude of prominent loyalists and sympathisers alike, the economic welfare of the community facilitated the post war reconciliation amongst, especially, the white populace of the Oudtshoorn district despite the bitterness that still prevailed after the war.
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    Microsatellite-based DNA fingerprinting of selected grapevine cultivars
    (South African Society for Enology and Viticulture, 2018) Van Heerden, C. J.; Burger, P.; Prins, R.
    Cultivar identification by ampelography is often difficult and is sensitive to environmental conditions, thus it can be problematic to distinguish between closely related cultivars. DNA fingerprinting offers an alternative method that is not influenced by the environment and is relatively easy to perform. However, discriminating between closely related individuals can be problematic if inadequate or insufficient markers are used. Following the estimation of null allele frequencies, an initial set of 35 microsatellite markers was reduced to 20 to generate unique DNA fingerprints for the majority of 111 different grape cultivars and breeding lines. Molecular evidence was utilised to evaluate the accuracy of the reported pedigrees for several cultivars bred in South Africa (SA). The use of markers linked to known downy mildew and powdery mildew resistance loci (Rpv3 and Ren3) provided information regarding the frequency of these resistance loci in the breeding material analysed.