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Title: Pepino mosaic virus : investigation into the molecular basis of symptomatic variation
Author: Duff-Farrier, Celia
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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Pepino mosaic virus (PepMV) is a destructive pathogen that poses a large threat to the tomato industry. Efforts to control its spread have failed and it now displays a global distribution. Its emergence has been characterised by the fast evolution of new necrotic strains and as of yet, the genetic basis for phenotypic aggression is unknown. Gaining an understanding of this is of the utmost importance in developing new control methods. Furthermore, natural known sources of resistance (R) genes are limited. The Rx gene from potato has shown to confer resistance when introduced as a transgene into the main crop of threat, tomato. However recent work suggests this resistance is easily overcome and highly unstable. The main aim of this project was to determine the genetic basis for the phenotypic aggression displayed by necrotic strains of PepMV, through the generation of chimeric PepMV infectious clones (ICs). Full-length ICs of both mild EU and aggressive CH2 forms of PepMV were generated, as well as chimeric viruses containing the 5' end of EU origin and either the 3' region (triple gene block and coat protein, CP) or CP of CH2 origin. Analysis of the phenotypes presented by these in a range of solanaceous indicator plants suggested that a pathogenicity determinant may reside in the CH2 CP region, and furthermore, this acted in a host specific manner. Additionally, during this investigation new mutants evolved from the constructed ICs, which displayed genotypic variation and altered pathogenicity. In combination this evidence shows that the genetic basis for phenotypic aggression of PepMV is highly complex and difficult to elucidate. The secondary aim of this project was to assess the stability of the Rx gene as a source of resistance against PepMV. The Rx-based resistance was found to be easily overcome by singular mutations occurring in the PepMV CP region, and would therefore not provide a suitable source of resistance to introduce into susceptible cultivars. Other RNA-based resistance strategies were also investigated. The generation of transgenic plants expressing full-length PepMV CP was found to have the potential to confer a high level of resistance to challenge with the cognate virus, as well as a mechanism based on RNA hairpin (HP) and viral co-inoculation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available