Browsing by Author "Swiegers, Hendrik Willem"

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    Comparing different siRNA delivery systems to target Diuraphis noxia
    (Stellenbosch : Stellenbosch University, 2018-12) Swiegers, Hendrik Willem; Botha-Oberholster, Anna-Maria; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.
    ENGLISH ABSTRACT: Diuraphis noxia, also known as the Russian wheat aphid, is a major pest of wheat. Breeding for resistance against D. noxia has been relatively successful in wheat as there has been many resistance genes incorporated into wheat in the past. However, this resistance has more often than not been counteracted by D. noxia through the development of a new biotype. The mechanism with which D. noxia is able to do this is not well understood. Previously, a highly virulent, laboratory generated biotype, known as SAM (South African Mutant), was compared to its avirulent progenitor, SA1, through proteome analysis of the salivary glands and complete genome sequence analysis. It was found that, among other differences, the cuticle protein, Dncprr1-8, containing a Rebers and Riddiford consensus was present in the salivary gland of SAM but not SA1. The gene also contained single nucleotide polymorphisms (SNPs) between the biotypes. In this study the function of Dncprr1-8 was investigated through RNA interference (RNAi). As RNAi has never been performed in D. noxia, several methods of siRNA delivery to this organism were compared. Injection of siRNA into the aphid haemolymph and ingestion of siRNA through artificial feeding medium was not successful. Allowing D. noxia to feed on wheat inoculated with a virus-induced gene silencing (VIGS) vector modified to contain D. noxia transcript sequence was partly effective, but overall had variable results. Finally, siRNA delivery through injection into wheat and allowing D. noxia to feed around the injection site, proved to be the most effective. Delivery of Dncprr1-8-siRNA using this method resulted in reduced survival and fecundity of biotype SAM while feeding on resistant wheat. The phenotypic responses were then compared to that of another aphid species, Myzus persicae, feeding on Arabidopsis thaliana injected siRNA targeting the same gene. M. persicae did not display reduced survival, but did produce fewer nymphs. Collectively, the results were then used to draw conclusions on the putative function of Dncprr1-8 in the plant-aphid interaction.