Charlotte Allender discusses the role of the UK Vegetable Genebank in finding plant health solutions:

Managing and preventing outbreaks of pests and diseases on our crops is a financially and environmentally expensive activity. Globally, crop losses due to pests and diseases may reduce yields by up to 40%. The application of chemical controls (including pesticides and fungicides) is an additional cost to farmers, and these substances can have unwanted environmental impacts. Finding another solution to the issue of managing crop pest and diseases is essential in order to support more sustainable food production and to improve to global food security.

Genetic variation within crops is an important resource to use to improve the health of our crops. Pest and disease resistances are valuable traits, and may be found in less utilised parts of the crop genepool, for example in populations of wild relatives of crops and in landraces (traditional varieties developed through many generations of selection by farmers). Crop genebanks like the UK Vegetable Genebank have the role of conserving crop genepool diversity to ensure it remains available for research and breeding. Valuable diversity is at risk of loss through habitat destruction for wild populations and historical changes to farming practices. Diverse landraces have been replaced by commercial varieties (which benefit crop production). Some of these landraces have been lost altogether, others only exist in genebank collections. Whilst many of these are not suited to modern, highly mechanised farming practices, they may harbour genes conferring resistance to plant pests and diseases.

The UK Vegetable Genebank manages a collection of around 14,000 seed samples of vegetable crops. Opened in 1980, our seed has been used around the world for research and crop improvement, often to screen to look for new sources of resistance to diseases such as black rot and clubroot, and pests such as carrot root fly and diamond back moth. Once a resistance trait has been identified, it is then possible to cross it into breeding lines for new varieties. It can be helpful to screen for DNA markers associated with the resistance trait in order to follow it more efficiently across generations in the breeding process.

You can hear from some researchers about how they use crop diversity in their research with the aim of improving resistance to pests and diseases.

Yao Lu discusses her PhD research on lettuce pinking:

Lettuce (Lactuca sativa L.), has become the fourth most popular vegetable in the market since the turn of the century and its commercial value ranks relatively high compared with other vegetables produced in the UK. It is mainly growing with leaves consumption in mind, but sometimes it is also grown for the stem and seeds. Many lettuce varieties commonly have short stems at the beginning of cultivation, but the stem and branches stretch during flowering and can display large heads, but this can differ in shape and color.

As a leafy vegetable, lettuce put on the market for consumption is mostly packing as ‘read-to-eat’. For fresh cut salads, however, are relatively perishable and will turn to discoloration which has been reported as a big issue about limiting shelf life on food market. This loss on lettuce quality can pose a significantly economic lose from producer, retailer to customers with up to 30% loss of total crop production among processing and harvesting and around 35% waste after purchasing, and the reason for causing this loss is basically due to mechanical operation. The processing technologies, mainly refer to cutting and/or slicing on lettuce, will shorten the shelf life conspicuously by leading to the discoloration or inducing the microbial reaction boom. For minimally processed salad packs, it normally takes a few days to observe the discoloration on the cut leaf edges and it could be damaged by a range of internal and external factors hence leading to a subsequence of discoloration caused by pigments in lettuce.

Wounding of lettuce tissues induces a number of physiological reactions like ethylene production, respiration increase, oxidative browning and/or secondary metabolites formed. Unfortunately, there are not too much research on distinguishing the browning and pinking, but pinking, actually, is an independent phenomenon occurring on some lettuce varieties.

Narrowly speaking, we think the pathway between browning and pinking is different. There are two reactions that Caffeic acid (CA) is involved, the action with quinic which is the natural acid compound from plants, they can release a few colorless o-diphenols. The other activity is under the participating of polyphenol oxidase and O₂, and produce caffeic acid o-quinones (CAQ) that presents as a pink colour. These o-quinones could transfer the coloured-o-quinones back to colourless-o-diphenols. Depends on the speed between colour and colourless transferring, the lettuce will show significant symptom of obvious pink or brown, in other words, the reduction of reaction and its production between CA to chlorogenic acid will lead to the accumulation of CA to CAQ and thus produce more pink compounds.

Unfortunately, it is not clear the factors which trigger pinking and browning within lettuce, so the aim of this project is to identify the regulators of these pathways in order to determine how such discoloration could be prevented.

On the base of carrying out a backcrossing experiment between the lines showing maximal discoloration within the Saladin x Iceberg mapping population previously used to identify QTL associated with pinking and browning phenotypes, the parents of the population on this project were choosing from the lines which were showing consistently high and low levels of pinking only from a field trail with a set of 94 F₇ recombinant inbred lettuce lines which are previously demonstrated variation in the development of pinking and browning discolouration.

For targeting the genes which might regulate the pink pathway, we analysed the transcriptome of pinking and browning RNA sequence and picked the genes that only performed as high and low pinking. And finally identified 8 genes to study the differences between the transcriptome of high pinking and low pinking lines.

By assessing RNA-seq , these 8 genes will be able to identify the expression differences of the putative regulators, and finally carrying out knockout experiments by using CRISPR to verify phenotype associated with the most likely regulator.

Lauren Chappell discusses her research as part of the VeGIN (Vegetable Genetic Improvement Network) project:

The spread of plants pests and diseases has increased dramatically in recent years. A combination of climate change, increased trade and decreased agrochemical availability have all played a part. With these many challenges faced by the food and farming industry there is a need for sustainable solutions.

VeGIN, the Vegetable Genetic Improvement Network, is one of several crop genetics projects funded by Defra. VeGIN has worked to create an interactive network of researchers and industry leaders, who work together to promote market delivery of improved vegetable varieties using sustainable production systems.

The VeGIN network brings together research focussed on four key vegetable crops – onion, carrot, leafy vegetables and salads - and encourages collaborations between industry and researchers to address how genetic improvement of crop varieties can contribute to a sustainable increase in food production to meet the twin challenges of food security and climate change. The ‘biotic’ or pest and disease research is carried out by the University of Warwick, whilst the ‘abiotic’ or physical challenges associated with climate change are being carried out by Harper Adams University. Industrial partners play an invaluable role, advising on key concerns within the horticulture industry as well providing feedback on the work being undertaken.

Clockwise from top left: Cabbage plant, carrots just harvested still covered in soil, onions growing in the field and beds of lettuce in the field.

The project utilises the genetic diversity in the Vegetable Genetic Resources Unit (GRU) which is also based at Warwick Crop Centre. The GRU has a remit for collection, conservation, characterisation and research for a range of vegetable crops and their wild relatives. The gene bank holds thousands of accessions representing different crop species. As these accessions characterise the range of genetic diversity within a single crop species, from wild type crop relatives to commercial varieties VeGIN can use these accessions representing a huge range of genetic diversity to identify genes of interest that can be used to breed more sustainable crops.

The primary airs of VeGIN are as follows:

· To develop the genetic resources and tools to accelerate breeding for ‘sustainability traits’ in field vegetables

· To establish an effective network with industry, for knowledge transfer to promote market delivery of research and development.

The list below indicates just some of the pests and diseases VeGIN are currently researching, both in identifying sources of resistance, and improving the knowledge of the pathogen/pest and plant system:

· Cavity spot caused by the Oomycete Pythium violae in carrots

· Clubroot in leafy brassicas cause by the fungus Plasmodiophora brassicae

·  Lettuce wilt cause by Fusarium oxysporum

· Willow-Carrot aphid infestation of carrot crops and the associated viruses the aphids transmit

· Currant-Lettuce aphid on lettuce crops

· Diamond-back Moth infestation of leafy brassica crops

· Cabbage Root Fly damage to leafy brassica crops

Clubroot resistant (right) and susceptible (left) brassica seedlings and Carrots with cavity spot damage from Pythium violae

If would like to learn more about VeGIN please visit the website (new website launching soon!), and follow us on twitter @WarwickVeGIN. If you would like more information about a specific project, would like to be added to the VeGIN mailing list or are an industry member looking to work together please email lauren.chappell@warwick.ac.uk