Elucidating mechanisms that underpin aphid-plant interactions
Date
2024-12
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Stellenbosch : Stellenbosch University
Abstract
Aphids are global pests of both crop and ornamental plants. Aphid infestations of crop plants result in yield losses through nutrient depletion and the spread of viruses. Although often effectively controlled by traditional chemical insecticides, these have deleterious effects on both the environment and human health. As such the use of insecticides have been restricted in some parts of the world. Secondly, many aphid populations have developed resistance to various insecticide classes. Host plant resistance offers an alternative to control aphid pests, however as with other control methods, aphids often overcome host resistance through the development of virulent biotypes. The aim of this project was to investigate the aphid-plant interaction by firstly examining differential gene regulation of aphid and host using virulent and avirulent Diuraphis noxia (Russian wheat aphid) biotypes feeding on a resistant Triticum aestivum (bread wheat) cultivar containing the D. noxia resistance gene, Dn7. The virulent D. noxia biotype SAMv2 exhibited distinct gene expression compared to the genealogically linked avirulent SAl, suggesting adaptations to overcome host resistance. SAMv2 upregulated transcripts implicated in detoxification (e.g. L-xylulose reductase) as well as other transcripts of unknown function. Transposable elements were highly active in all biotypes and to a lesser extent, epigenome modifying enzymes, potentially contributing to rapid adaptation to its host. T. aestivum responded to aphid feeding with jasmonic acid signalling and terpene biosynthesis. However, virulent SAMv2 appeared to modulate these defence mechanisms as monoterpenoid and diterpenoid biosynthesis were only upregulated following feeding by avirulent biotypes SAS and SAl, respectively. It was also found that the strigolactone synthesis gene, CYP711A1 was upregulated following feeding of biotype SAS. Secondly, the effect of elevated CO2 and strigolactones on Pisum sativum (pea) susceptibility to Acyrthosiphon pisum (pea aphid) were investigated. A. pisum performed better on strigolactone synthesis and signalling P. sativum mutants while [CO2] had no effect on aphid fecundity. The lower gibberellic acid levels observed in the strigolactone mutants were significantly correlated with increased A. pisum fecundity. Lastly, the function of cuticle protein, CpRRl-8, in the formation of virulence in D. noxia was also investigated. This work provides a foundation for developing more effective and sustainable aphid control strategies. Future research building on these findings will continue to
uncover the dynamics of aphid-plant interactions and contribute to the development of resilient agricultural systems.
Description
Thesis (PhDAgric)--Stellenbosch University, 2024.