Armitage, Andrew D. (2013) Alternaria alternata leaf spot pathogens : genetics, evolutionary history and diagnostics. PhD thesis, University of Warwick.

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Abstract

The primary objective of this study was to characterise the Alternaria alternata species group. Particular focus was put on understanding the pathogens Alternaria mali and Alternaria gaisen, responsible for leaf spot diseases of apple and pear and of phytosanitary importance in Europe. Understanding evolutionary relationships is important in defining the genetic and biological characteristics associated with plant pathogens in this species group. This will inform management strategies and facilitate the development of reliable detection tools for important plant diseases.

Evolutionary relationships within the A. alternata species group were established using a phylogenetic approach based on functional genes. Highly variable loci (endoPG, Alta1, L152 and three novel loci) identified three major lineages within the A. alternata which were supported by isolate morphology. These were considered to represent subspecies within A. alternata.

The presence of toxin-synthesis genes, required for the production of host-selective toxins (HSTs) in apple and pear pathotypes, was established within A. alternata isolates. Isolates carrying apple HST-genes were only present in ssp. tenuissima, while isolates carrying pear HST-genes were present in ssp. gaisen. Virulence assays showed that apple HST-genes are required for pathogenicity on apple leaf.

The presence of different mating type genes in isolates was used to assess evidence for recombination within the A. alternata species group. Distribution of mating type idiomorphs indicated that recombination must have occurred in this putatively asexual species. Analysis of whole genome sequence data indicated that A. alternata possesses the genes required for meiotic recombination, supporting a theory of recombination and possible sexuality within this group.

This work provides insight into the evolution and causal agents of A. alternata plant diseases. Furthermore, whole genome sequencing data was generated during the course of this study and represents valuable genetic resource that can be used for future research, including development of pathotype-specific molecular markers.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QK Botany
Library of Congress Subject Headings (LCSH):	Alternaria -- Genetics
Official Date:	December 2013
Dates:	Date Event December 2013 Submitted
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Sreenivasaprasad , S. ; Lane, Charles ; Woodhall, James ; Barbara, Dez J. ; Clarkson, John P.
Sponsors:	Great Britain. Department for Environment, Food & Rural Affairs
Extent:	xii, 262 leaves : illustrations, charts
Language:	eng

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