Smith, Madeleine Joy (2008) The biology and molecular biology of Polymyxa species and their interactions with plants and viruses. PhD thesis, University of Warwick.

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Abstract

Polymyxa graminis and Polymyxa betae are obligate, intracellular, root-infecting organisms of cereals (P. graminis) and members of the Chenopodiacae (P. betae). Between the two species, they transmit approximately 15 economically important plant viruses. These include Soil-borne cereal mosaic virus, Barley yellow mosaic virus and Beet necrotic yellow vein virus and together, cover a world-wide distribution. Recent ribosomal DNA (rDNA) sequence data has shown that temperate isolates of P. graminis belong to two groups or ‘ribotypes’ based on sequence differences in the internal transcribed spacer region. P. betae sequences belong to a third group. These ribotypes appear to differ in host range and ability to transmit viruses. It has been suggested that particular ribotypes have different host specificities or preferences and are involved in the transmission of specific viruses. There were three major areas of work. Firstly the determination of host-virusribotype associations. One approach was to inoculate plants containing virus with specific ribotypes and monitor onward transmission of the virus to a susceptible host. Another approach used plants grown in infested soils to bait any Polymyxa present, then plants were tested for the Polymyxa ribotypes and viruses present. This work confirmed the association between ribotype II and SBCMV and SBWMV, using viruses from a wider range of geographic locations. It also identified a previously unknown role for transmission of Furoviruses by P. graminis ribotype I. Examination of the phylogenetic relationships of Polymyxa ribotypes using rDNA sequences revealed two new ribotype groups. Whilst ribotype groups II, IV and V always form a clade together, the relationship of the other P. graminis ribotypes and P. betae is still not well resolved. Finally, for the first time, infection of Arabidopsis by Polymyxa (P. betae and P. graminis) was demonstrated, showing that this model system could be used to study Polymyxa-host interactions.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QK Botany
Library of Congress Subject Headings (LCSH):	Plants -- Viruses, Roots (Botany) -- Diseases and pests, Protista -- Genetics, Arabidopsis -- Viruses
Date:	October 2008
Institution:	University of Warwick
Theses Department:	Warwick HRI
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Adams, Michael J. ; Ward, Elaine ; Walsh, John A.
Extent:	211 leaves
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/3792

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