Swanepoel P.A.,Stellenbosch University |
Swanepoel P.A.,Outeniqua Research Farm |
Du Preez C.C.,University of the Free State |
Botha P.R.,Outeniqua Research Farm |
And 2 more authors.
Soil Research | Year: 2015
Soil quality of pastures changes through time because of management practices. Excessive soil disturbance usually leads to the decline in soil quality, and this has resulted in concerns about kikuyu (Pennisetum clandestinum)-ryegrass (Lolium spp.) pasture systems in the southern Cape region of South Africa. This study aimed to understand the effects of tillage on soil quality. The soil management assessment framework (SMAF) and the locally developed soil quality index for pastures (SQIP) were used to assess five tillage systems and were evaluated at a scale inclusive of variation in topography, pedogenic characteristics and local anthropogenic influences. Along with assessment of overall soil quality, the quality of the physical, chemical and biological components of soil were considered individually. Soil physical quality was largely a function of inherent pedogenic characteristics but tillage affected physical quality adversely. Elevated levels of certain nutrients may be warning signs to soil chemical degradation; however, tillage practice did not affect soil chemical quality. Soil disturbance and the use of herbicides to establish annual pastures has lowered soil biological quality. The SQIP was a more suitable tool than SMAF for assessing soil quality of high-input, dairy-pasture systems. SQIP could facilitate adaptive management by land managers, environmentalists, extension officers and policy makers to assess soil quality and enhance understanding of processes affecting soil quality. © CSIRO 2015.
Lyle R.,Agricultural Research Council Plant Protection Research Institute
African Invertebrates | Year: 2015
Two new species of trachelids of the Afrotropical genus Afroceto Lyle & Haddad, 2010 are described. Both species, A. ansieae sp. n. and A. dippenaarae sp. n., are endemic to South Africa. An updated identification key to males of the genus is provided. © FUNPEC-RP.
Bahramisharif A.,Stellenbosch University |
Lamprecht S.C.,Agricultural Research Council Plant Protection Research Institute |
Spies C.F.J.,Stellenbosch University |
Spies C.F.J.,Agriculture and Agri Food Canada |
And 2 more authors.
Mycologia | Year: 2013
The genus Pythium consists of more than 120 species and is subdivided into 11 phylogenetic clades (A-K) based on internal transcribed spacer (ITS) region sequence data. Pythium clade G contains only seven known species, with most not being well described. Our study characterized 12 Pythium isolates from Aspalathus linearis (rooibos) that fit into clade G. Phylogenetic analyses of the ITS region and a combined phylogeny of four gene regions (ITS, b-tubulin, COX1 and COX2 [cytochrome c oxidase subunits I, II]) identified five clade G subclades. The rooibos isolates formed two groups, Pythium Rooibos I (RB I) and II (RB II), that clustered into two separate clades within subclade 1. The nine Pythium RB I isolates formed a distinct clade from P. iwayamai and is described here as a new species, Pythium cederbergense sp. nov. The three Pythium RB II isolates had P. canariense and P. violae as their closest relatives and were genetically diverse, suggesting the presence of several new species or a species complex that cannot be resolved with the current data, thus precluding a species description of this group. Morphological analyses showed that P. cederbergense and Pythium RB II were indistinguishable from each other but distinct from known clade G species. Clade G studies are being hampered by imprecise morphological descriptions of P. violae, P. canariense and P. iwayamai and each species being represented by only one isolate. The P. cederbergense and Pythium RB II isolates all were nonpathogenic toward rooibos, lupin and oats seedlings. One oligonucleotide was developed for each of P. cederbergense and Pythium RB II, which was able to differentiate the isolates with DNA macro-array analyses. © 2013 by The Mycological Society of America.
Oldroyd B.P.,University of Sydney |
Allsopp M.H.,Agricultural Research Council Plant Protection Research Institute |
Lim J.,University of Sydney |
Beekman M.,University of Sydney
Evolution | Year: 2011
The honey bee population of South Africa is divided into two subspecies: a northern population in which queenless workers reproduce arrhenotokously and a southern one in which workers reproduce thelytokously. A hybrid zone separates the two, but on at least three occasions the northern population has become infested by reproductive workers derived from the southern population. These parasitic workers lay in host colonies parthenogenetically, resulting in yet more parasites. The current infestation is 20-year old-surprising because an asexual lineage is expected to show a decline in vigor over time due to increasing homozygosity. The decline is expected to be acute in honey bees, where homozygosity at the sex locus is lethal. We surveyed colonies from the zone of infestation and genotyped putative parasites at two sets of linked microsatellite loci. We confirm that there is a single clonal lineage of parasites that shows minor variations arising from recombination events. The lineage shows high levels of heterozygosity, which may be maintained by selection against homozygotes, or by a reduction in recombination frequency within the lineage. We suggest that the clonal lineage can endure the costs of asexual reproduction because of the fitness benefits of its parasitic life history. © 2010 The Author(s). Evolution © 2010 The Society for the Study of Evolution.
Simelane D.O.,Agricultural Research Council Plant Protection Research Institute |
Simelane D.O.,University of Cape Town
Biological Control | Year: 2010
A root-feeding flea beetle, Longitarsus bethae Savini & Escalona (Chrysomelidae: Altcinae), was introduced into South Africa to complement the impact of the above-ground insect agents already established on Lantana camara L. (Verbenaceae). To estimate the potential effectiveness of L. bethae for biological control of L. camara, growth of various plant components were measured under different levels of abundance of the insect under quarantine glasshouse and semi-field conditions. Populations of L. bethae larvae that developed in previously-sterilized soil from initial cohorts of 200 and 300 eggs per plant significantly stunted the growth of L. camara, causing reductions in the number of leaves, stem height, stem diameter, above-ground dry-mass, and below-ground dry-mass, of up to 54%, 21%, 31%, 34% and 40%, respectively. Compared with the controls, the larval population resulting from an inoculum of 100 eggs per plant usually had no statistically significant effect on plant growth. The degree of root damage caused by the larvae was directly proportional to the number of eggs added and to the number of adults that emerged. Under semi-field conditions, cumulative herbivory by L. bethae adults and larvae during a six-month period caused severe leaf and root damage, resulting in a cumulative decline of 148% in flower production. Overall, the ability of L. bethae to both directly suppress root growth and indirectly suppress leaf production, stem growth and flower production of L. camara, indicates that this flea beetle has the potential to make a considerable impact on the weed's invasiveness in South Africa. © 2010 Elsevier Inc.