A genetic approach to improving post-harvest quality

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The research aims to provide tools for breeding crop varieties with reduced propensity for postharvest discolouration. The crop system for study is postharvest discolouration in lettuce which is a major problem for the UK salad supply chain. A reported 97,000 tonnes of whole head lettuce and bagged salad are wasted annually in the UK at a cost of £234m. A major cause of this is post harvest loss of quality due to discolouration (pinking and browning). We will use a multidisciplinary approach involving phenotyping, QTL analysis, bioinformatics, genomics, transcrptomics and metabolomics to achieve the following objectives.
1. Increase understanding of the genetics of pinking and browning in lettuce
2. Determine the role of phenylpropanoid (PP) pathway in lettuce discolouration.
3. Determine whether non PP pathway genes have a role in lettuce discolouration
4. Test the robustness of a genetic approach to reducing discolouration
5. Identify potential sources of beneficial alleles for key genes.
6. Assess the potential impact on pest and disease resistance and taste.
7. Test the applicability of the findings from lettuce to cabbage and apple.

Industry partners from the supply chain will provide expertise in breeding, crop agronomy and production and processing and consumer acceptance.
We will use an improved lettuce linkage map and an F7 RIL population to carryout QTL and eQTL analysis in order to understand the role of PP pathway genes in determining phenotypic variation. We will use RNA seq combined with bulk segregant analysis and also exploit lettuce sequence data to attempt to identify new genes associated with discolouration. A lettuce diversity set will be mined to identify beneficial alleles for use in smart breeding aimed at improving the discolouration phenotype while minimising the impact on other agronomically important traits. We will carry out an initial assessment of the applicability of our results to other crops (apple and cabbage)

The ultimate beneficiaries of this research will be consumers who rely on visual appearance to judge quality of fresh produce. Discolouration is one of the major factors limiting current designated shelf life of fresh produce and one of the most common reasons for product failing to meet shelf life targets making it a major cause of food waste post-purchase. The minimum requirement for shelf life of pre-packed lettuce to the consumer is currently five to six days however, salad packs generally only survive three days from time of purchase until 'end of life' and it is estimated that 97,000 tonnes of whole head lettuce and bagged salad are wasted in the UK at a cost of £234m. The main cause of this wastage was loss of quality in a relatively short time (i.e. short shelf life). There is therefore a high demand from consumers for products with longer shelf life.
The research will have wider societal benefits by reducing food wastage and resultant reduction in wastage of inputs such as fertilizer, water and pesticides as well as leading to improved land use through improved marketable yield.
Other stakeholders in the lettuce supply chain will also benefit from the research as it will lead to improved postharvest shelf life of fresh produce which will reduce waste, reduce costs and delivery of consistently good quality products.
Lettuce breeders will benefit directly from the research as it will provide underpinning knowledge and molecular breeding tools to facilitate breeding of lettuce varieties with reduced propensity to develop post harvest discolouration. Rijk Zwaan as a partner in this project will exploit the results directly in their lettuce breeding programme and expect to have developed lettuce varieties with improved phenotype for post harvest discolouration 5-10 years from completion of the project.
Processors and retailers of fresh produce will benefit from the research because it will lead to development of improved raw materials for their products. Currently modified atmospheric packaging (MAP) can be used to control discolouration and prolong shelf life. However, this technique has a number of disadvantages and limitations. These include: added production costs; the need for specialised equipment and significant imprecision. The huge natural variation in raw materials makes it almost impossible to optimise gas formulations for each product and complex mixed leaf packs inevitably create compromises. More importantly, once a pack is opened, oxygen re-enters resulting in development of discolouration after purchase, the consumer therefore gains little from MAP. More aggressive MAP approaches for fresh produce (e.g. packaging in targeted anaerobic conditions) are not widely adopted because of the potential impact on food safety - a result of an increased risk of growth of anaerobic human pathogens. In addition, MAP is not used with whole heads either for retail or raw material for a processing factory (where they may be held in an intake store for 7-10 days). Breeding of new varieties with improved shelf life will remove or reduce the need for MAP reducing production costs and improving product quality throughout the supply chain. The value of the project to the supply chain is illustrated by the involvement of Bakkavor (the largest processor of fresh produce in the UK ) in the project. Lettuce growers will benefit from the research. Growing conditions have been shown to influence postharvest discolouration particularly the timing of water availability; however, this is difficult to control in UK field crops. Breeding crop varieties with an inherent reduced propensity to discolour regardless of the growing environment is a sustainable and cost effective way to address the problem as growing such varieties has no added production costs and will reduce costs due to wastage. The value of the research to lettuce growers is illustrated by the involvement of Gs Fresh (the largest UK salad growers) in the project.