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A major concern in the food industry is the post harvest discolouration of fruit and vegetables. The shelf life of many products, but particularly that of cut lettuce is regularly restricted by enzymatic browning and pinking. During storage their organoleptic characteristics are visibly altered which generally incites an unfavourable consumer response. The phenylpropanoid pathway synthesises polyphenols that are subsequentially oxidised by polyphenol oxidase (PPO). PPO is the main agent responsible for enzymatic browning, although a synergistic effect between PPO and peroxidases is possible. Phenylalanine ammonia-lyase is the rate-limiting enzyme of the pathway normally induced upon wounding of plant tissue, thus increasing polyphenol biosynthesis for oxidation. Anthocyanin pigments are secondary phenolic metabolites which sequentially accumulate causing undesirable pinking due to their associated red colour. Post harvest discolouration is currently delayed by combinations of post harvest treatments. A genetic engineering approach would allow regulation of the pathways, avoiding treatment use. However widespread public opinion opposes this type of modification. The current project aims to provide resources for breeding improved ‘shelf life’ through the exploitation of natural allelic variation and an understanding of the genetics of post harvest browning and pinking.
Aims of the Project
1) Determine the genetics of post harvest discolouration in lettuce.
Produce a new improved linkage map for F7 Saladin x Iceberg lettuce recombinant lines (RILs) using fluorescent AFLP markers and expressed sequence tags (ESTs).
Screen the lettuce accessions held within the Genetic Resources Unit (GRU) at WHRI for both types of discolouration. Analyse where parents of the F7 population lie within the accession distribution and whether the mapping population is representative of the range of natural variation.
Induce and phenotypically assess post harvest browning and pinking from replicated field trials of 94 F7 in addition to the parents.
Carry out quatitative trait loci (QTL) analysis for post harvest discolouration in lettuce utilising the F7 linkage map and identify potential markers of value in lettuce breeding.
2) Metabolite analysis of the process producing post harvest discolouration.
Identify candidate lettuce ESTs with sequence homology to genes potentially involved in both pathways from Arabidopsis and potato will be identified.
Conduct gene expression studies for the selected genes, again on the two parents and selected RILs. Relevant ESTs will be mapped to determine whether they are positioned within any QTL. Results will be utilised to identify genes associated with the two discolouration responses of browning and pinking.
Analyse selected metabolites associated with both the phenylpropanoid and PPO pathway of the two parents and selected RILs with extreme phenotypes.
My PhD is also linked to an EU Genetic Resources project: EU FP6 Targeted Action: Leafy Veg, with Astley D, Pink D, Warwick HRI, EU FP6, Project Start Date: 01/06/2006 Project End Date: 31/05/2010.
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University of Warwick
University of Warwick
Dr Johan Schut
Rijk Zwaan Zaadteelt en Zaadhandel BV
PO Box 40
NL-2678 ZG De Lier