Talk and abstract both entitled 'Genetic Analysis of Post Harvest Spoilage in Lettuce' were given/submitted. Please contact L.D.Atkinson@warwick to request copy of the talk (due to unpublished results).
Genetic Characterisation of Post Harvest Spoilage in Lettuce
Supervisors: D. A. C. Pink1, V. Buchanan-Wollaston1and J. Schut2
1 WarwickHRI, University of Warwick, Wellesbourne, Warwick,
CV35 9EF, UK
2 Rijk Zwaan, Burgemeester Crezeelann 40, Postbus 40, 2678 ZG De Lier Holland
A major concern in the food industry is post harvest discolouration of fruit and vegetables which generally incites an unfavourable consumer response. The shelf life of cut lettuce salad packs is regularly restricted by enzymatic browning and pinking. Pinking is due to accumulation of anthocyanins through the phenylpropanoid pathway and browning occurs due to oxidation of polyphenols by polyphenol oxidase. The enzyme phenylalanine ammonia-lyase increases polyphenol biosynthesis for oxidation upon wounding of plant tissue.
Post harvest discolouration is currently delayed by combinations of post harvest treatment. Production of genetically improved lines with reduced likelihood for discolouration would avoid the need for such treatment. Genetic engineering could be used to manipulate the biochemical pathways, however, currently public opinion opposes this approach; an alternative is to exploit genetic variation in lettuce for post harvest discolouration through a conventional breeding approach. The current project aims to provide resources for breeding improved ‘shelf life’ and an understanding of the genetics of post harvest browning and pinking.
Post harvest discolouration has been induced in a lettuce diversity set and discolouration phenotypically assessed when cut and bagged using an objective scoring system. The F7 mapping parents, Saladin and Iceberg showed differences for the two discolouration responses and overall discolouration. Iceberg appears more susceptible for browning, whilst Saladin appears more susceptible to pinking. Differences early on are of greater importance to the food processor due to the products limited life on the shelf before the best before date expires. The differences between the parents covers a major part of the range seen in the diversity set so the mapping population is suitable to carry out genetic analysis for these traits.
A new improved linkage map based on 125 F7 Saladin x Iceberg RILs has been created using AFLP, COS, EST and SNP markers. Over 200 markers mapped resulting in coalescence into 15 linkage groups covering all 9 chromosomes, with a map length of >723 cM.
Post harvest discolouration in the 94 F7 RILs and the two parents was induced in replicated field trials and assessed. This resulted in the identification of 18 significant QTLs for discolouration (including pinking and browning, summarised and individually) for UK and Netherlands sites. QTLs were detected on 4 linkage groups with the majority on group 4 which co localised. Additionally some environment specific QTLs were observed for the data collected in the Netherlands.
An intensive field trial will be conducted in 2009 for the most extreme discolouration lines to gain a more thorough understanding of the discolouration response. Furthermore, relevant selected associated metabolites from the parents and extreme phenotypic F7 RILs will additionally be analysed by HPLC and enzyme assays to aid identification of compounds associated with the discolouration processes.
Project is principally funded by BBSRC with the industrial partner Rijk Zwaan.
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