Browsing by Author "Knoetze, Rinus"
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- ItemFirst report and molecular characterization of the dagger nematode, Xiphinema oxycaudatum (Nematoda, Dorylaimidae) from South Africa(Pensoft, 2019-12-03) Daramola, Fisayo Y.; Knoetze, Rinus; Swart, Antoinette; Malan, Antoinette P.Plant-parasitic nematodes of the genus Xiphinema Cobb, 1913 comprise a complex group of nematode species, some of which are important vectors of plant viruses. During a field survey to determine the soil health of an abandoned honeybush (Cyclopia genistoides) monoculture, a high density of the dagger nematode, Xiphinema oxycaudatum Lamberti & Bleve-Zacheo, 1979 (Nematoda, Dorylaimidae), was observed in soil around the roots of honeybush plants in an abandoned farmland at Bereaville, an old mission station in the Western Cape province of South Africa. Soil samples were taken from the rhizosphere of plants and nematodes were extracted from the soil using a modified extraction tray method. Specimen of the dagger nematodes were processed for scanning electron microscopy, morphological and molecular analysis. Molecular profiling of the nematode species was done in order to give an accurate diagnosis and to effectively discriminate the nematode from other species within the Xiphinema americanum group. Phylogenetic analysis based on the D2D3 expansion segment of the 28S gene supported a close relationship of species within the americanum group, however, the protein-coding cytochrome oxidase (coxI) of the mitochondrial gene provided a useful tool for distinguishing the nematode from other species within the group. This study represents the first report of X. oxycaudatum from South Africa.
- ItemA molecular, morphological and biological characterisation of the genus Globodera (Nematoda: Heteroderidae) in South Africa(Stellenbosch : Stellenbosch University, 2014-03) Knoetze, Rinus; Swart, Antoinette; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: A molecular, morphological and biological characterisation of the genus Globodera (Nematoda: Heteroderidae) in South Africa is presented. The aims of the study were to determine the spread of the genus in South Africa; to study the systematics and describe the characteristics of the group and to gain a more complete understanding of the biology of the group as agricultural pests. Surveys were conducted in the Cape Floristic Region and in all the potato-producing areas of South Africa. The surveys unearthed new species of cyst nematodes and determined the spread of Globodera rostochiensis in the country. Phylogenetic analysis of sequences from ITS-rDNA was used to infer phylogenetic relationships among cyst nematodes from South Africa. The analyses established the distinct phylogenetic positions of cyst nematode populations from South Africa relative to an array of other cyst nematode species and indicated the existence of four new species of cyst nematodes. Analysis of random amplified polymorphic DNA (RAPD) banding patterns revealed intraspecific genetic variation amongst populations of Globodera rostochiensis. In order to provide molecular protocols for the accurate identification of South African cyst nematodes, species-specific primers and restriction enzymes were tested for their ability to discriminate between local Globodera spp. A combination of the molecular, morphological and morphometric characteristics of these populations were used to describe three new species of cyst nematodes. Experiments to determine the effect of storage temperature on the viability and hatching of South African populations of G. rostochiensis, showed differences in the responses of different populations to different storage temperatures. Experiments to determine the effect of field conditions on the viability and hatching of South African populations of G. rostochiensis, indicated that a decline in viable eggs in cysts from different populations occur, but suggests that the cysts will be able to survive for much longer in these soils than was expected. Spontaneous hatch was the main contributor to the decline of viability of cysts in the soil. Recording of soil temperatures in different locations indicated that the average temperature at 20 cm depth was approximately 20°C, the optimum temperature for the reproduction of G. rostochiensis, as confirmed by in vitro reproduction tests, which also showed that multiplication and survival is influenced negatively when the temperatures rise above 25°C. Reproduction on differential potato clones confirmed the pathotype of all the South African populations of G. rostochiensis as Ro1. After assessing the reproduction of G. rostochiensis on indigenous solanaceous plants, it was concluded that none of these plants induce substantial hatch in G. rostochiensis, nor do they support multiplication of the nematode. The results of this project have an impact on inquiries at all taxonomic levels, while also having an essential practical application in nematology. Knowledge of the distribution, pathogenicity, survival potential and reproduction capacity of Globodera species in South African soils are valuable for the design of effective management strategies as well as regulatory measures.
- ItemPotential of the polymerase chain reaction for the identification of plant-parasitic nematodes(Stellenbosch : Stellenbosch University, 1999) Knoetze, Rinus; Stellenbosch University. Faculty of . Dept. of .