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 project objectives. 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 mapping population to carry out genetic analysis in order to understand the role of phenylpropanoid pathway genes in determining phenotypic variation and 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 also carry out an initial assessment of the applicability of our results to other crops (apple and cabbage).
Minimal processing adds significant value to fresh produce, however, it also increases its perishability reducing shelf life and leading to waste of the produce and the resources used to grow it. This project is aimed at post harvest discolouration, a significant cause of quality loss in a wide range of fresh produce such as sliced apple, cut cabbage and lettuce. The main issue we are addressing is postharvest discolouration of lettuce in salad packs. UK lettuce production/imports are worth £240m farm gate but the retail value of UK processed salads is £800m. However, Tesco have recently reported that 68% of their salads are thrown away; the situation is similar for other retailers. There is therefore a need to improve postharvest quality to reduce waste and deliver consistently good quality products to consumers. Modified atmosphere packaging can provide control but once the pack is opened oxygen enters resulting in discolouration. Growing conditions also influence postharvest discolouration but are difficult to control in field crops. We are proposing breeding lettuce varieties with reduced propensity to discolour as a way to address the problem. To do this we need to understand the genetics and biochemistry of discolouration.
We are building on previous research we have done which identified genetic factors controlling the amount of pinking and/or browning that developed on lettuce leaves in salad packs 3 days after processing. However, we do not know what compounds or which genes are involved and we now intend to find this out by a multidisciplinary project involving three universities; Harper Adams University, Reading and Warwick, a lettuce breeding company, a lettuce grower, a salads processor and the Horticulture Development Company.
We have produced a set of experimental lettuce lines which we know show differences in the amount of pink or brown discolouration they produce. We will grow and process these lettuces in a way that mimics commercial production. We will then assess the salad packs for the amount of discolouration developing over 3 days, which is the current best before date for supermarket salads. We can then link this information to the plant's DNA profile to identify genetic factors for discolouration and DNA markers which can be used by plant breeders.
The same lettuces will also be analysed for compounds produced by a biochemical pathway called the phenylpropanoid pathway. This is thought to produce the pigments that cause discolouration. We know from other studies in a plant called Arabidopsis the genes which control the phenylpropanoid pathway and we have found the same genes in lettuce. We will see how these genes behave in lettuce plants that produce a lot of discolouration and ones that don't discolour. We will also see how the genes behave under different growing conditions. We can link these gene expression patterns to the amount of pinking and browning to see which genes are the key ones. Once we have done this we can look for naturally occurring versions of the genes which give a reduced discolouration.
The compounds produced by the phenylpropanoid pathway influence other things such as pest and disease resistance, taste etc. We do not want to reduce the amount of discolouration by breeding but end up with lettuce susceptible to pests or with poor taste, so we will assess lines which show high discolouration or no discolouration for their resistance to aphids and mildew and for taste to see if there are any differences. There are some compounds produced by the pathway which are colourless but still provide some resistance so by knowing the genetics and biochemistry breeders will be able to carry out 'smart' breeding.
We will see if the results for lettuce hold true for other crops by seeing how the key genes behave in apple and cabbage and whether this is related to the amount of browning that develops when they are processed and look for genetic differences in these crops.
BBSRC Horticulture & Potatoes Initiative
Harper Adams University
Warwick University, Reading University, UC Davis, Rijk Zwaan BV, Gs Fresh, Bakkavor, HDC