Atkinson, Laura Denise (2010) Genetic characterisation of post harvest spoilage in lettuce. PhD thesis, University of Warwick.

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Abstract

Post harvest discolouration in lettuce is an increasingly important problem due to the shift in
the market for prepacked processed salads. Variation in post harvest discolouration was
recorded in a lettuce diversity set of 28 accessions representative of the lettuce genepool.
The parents of the WHRI lettuce mapping population, Saladin and Iceberg were included in
the diversity set. They showed significantly different responses for discolouration and the
difference between them was representative of a major part of the variation seen in the
diversity set. F7 RILs derived from a cross between Saladin and Iceberg were suitable for
genetic analysis of post harvest discolouration. As a precursor to the genetic analysis, a good
quality linkage map based on the F7 Sal x Ice population was generated. Significant genetic
variation in the post harvest response was demonstrated for these RILs. Twenty-one
significant QTL were identified for post harvest discolouration traits, and the markers linked
to the QTL can be used for marker assisted selection. Significant but weak correlations were
recorded between discolouration and important agronomic traits, however as these were not
highly correlated this means that post harvest discolouration and agronomic traits can
generally be independently selected for by breeders without having to compromise on other
traits. Research was also initiated to understand the metabolic changes underlying the
phenotype change. Significant variation in levels of metabolites related to post harvest
discolouration including phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO)
and total phenolic content (TPC) was observed in RILs with extreme phenotypes. The
differences in metabolite levels were significantly correlated with the discolouration
phenotypes. Work was also initiated to identify candidate genes associated with the
biosynthetic pathway responsible for discolouration (phenylpropanoid pathway) in an
attempt to identify genes underlying QTL. Twenty-three genes have been placed on the Sal
x Ice map using comparative genomic approaches. Some of these co-locate within the
region of a discolouration QTL and are therefore candidate genes for the QTL effect.
Mutants with altered post harvest discolouration phenotypes were also confirmed in this
study; however the point of mutation could not be identified although it is thought to be
downstream of PPO. This indicates that a desired phenotype with reduced levels of post
harvest discolouration can be achieved by two approaches to breeding; using natural and
induced variation. This study has provided the tools and knowledge to do this.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QK Botany S Agriculture > SB Plant culture
Library of Congress Subject Headings (LCSH):	Lettuce -- Genetics, Lettuce -- Postharvest diseases and injuries, Lettuce -- Metabolism
Official Date:	September 2010
Dates:	Date Event September 2010 Submitted
Institution:	University of Warwick
Theses Department:	Warwick HRI
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Pink, David
Sponsors:	Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC) ; Rijk Zwaan (Firm)
Extent:	xv, 353 leaves : ill., charts
Language:	eng

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