Seminar: Aphid-host interactions: It’s about host resistance, aphid virulence and pest control
Seminar presented by Anna-Maria Botha (Genetics, Stellenbosch University)
Aphids are a group of approximately 4,700 species of phloem-feeding insects with mainly temperate distributions. Although best known as agricultural pests, they are also valuable systems to study host plant specialisations, bacterial symbiosis and environmentally induced morphologies (polyphenism). Diuraphis noxia (Kurdjumov, Hemiptera: Aphididae), a specialist phloem feeder, is such economically important cereal aphid pest afflicting wheat and barley yield in dry-land production regions. Unlike in areas where D. noxia is endemic and can reproduce through facultative parthenogenesis, in areas were it is invasive, it reproduce only asexually. Despite the lack of sexual recombination, new D. noxia biotypes with varying levels of virulence continue to develop and overcome previously resistant host plants, posing multiple threats to global food security. Host plant resistance, the most environmentally sound measure of pest resistance is defined by the response to aphid feeding (i.e., antibiosis, antixenosis or tolerance), with most Dn genes following the gene-for-gene relationship. With the availability of the draft genome of D. noxia and confounding evidence of genomic plasticity, we set out to determine the extent of DNA methylation in the genome of D. noxia in order to determine if epigenetic regulation contributes to changes in virulence. To this end, the global levels of methylation as well as the methylation profiles of the different biotypes were investigated. The global and specific methylation results suggest an inversely proportional relationship between virulence levels and DNA methylation, and that methylation may be associated with increased virulence. This study, being the first of its kind for D. noxia, has provided the groundwork for future research into methylation of this insect, and adds to a growing body of knowledge on hemipterans.
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