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Yield, quality and shelf-life problems in lettuce due to virus infections in the UK (Ref: CTP-SAI-059)


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  Dr Charlotte Nellist, Dr J Walsh, Ms Emma Garfield  No more applications being accepted  Funded PhD Project (Students Worldwide)

About the Project

Intensive farming and sequential plantings of lettuce crops in the UK mean lettuce is grown in the same fields for the whole season (March-October). This makes them vulnerable to plant diseases and results in a build-up of pathogens, particularly viruses. Very little is known about which viruses are infecting lettuce in the UK, the incidence of these viruses and their impact on lettuce quality and yield. In 2015 there was a major virus problem in lettuce in the UK resulting in the loss of 14 million lettuce heads that were ploughed in due to virus infection. Lettuce is predominantly grown outdoors in the UK and plant maturity can take between 6-10 weeks depending on the time of the season. The loss of neonicotinoid insecticides has resulted in the increase of insect virus vectors in crops, particularly aphids. This is exacerbated by some viruses having very wide host ranges resulting in adjacent weed species and beneficial pollinator field margins serving as reservoirs. 

Our preliminary data from the 2021 season identified two viruses within a crop in Cambridgeshire. Turnip yellows virus (TuYV) was found infecting both lettuce and adjacent weed species. TuYV infection was detected by enzyme-linked immunosorbent assay (ELISA) and confirmed by RT-PCR and sequencing.  TuYV was by far the most frequent virus detected and is known to have a significant effect on the quality, development, yield (up to 65% reduction) and storability of vegetable brassicas and incidences of up to 100% have been reported for TuYV in oilseed rape (OSR) and vegetable brassica crops, providing a reservoir of the virus. Other than TuYV, the only other viruses that have been reliably and conclusively identified in lettuce crops in the UK in recent years are cucumber mosaic virus (CMV) and lettuce mosaic virus (LMV, which is seed-borne) in 2015.


The main project objectives are:

  1. To determine what are the current virus species infecting UK lettuce crops
  2. Investigate the virome of lettuce crops and characterise viral diversity within UK lettuce crops
  3. Quantify the impact of the viruses infecting lettuce in the UK on yield, quality and shelf-life of lettuce
  4. Identify and characterise TuYV resistance from diverse lettuce genotypes and wild relatives


  1. Field surveys will be conducted to investigate the virome of UK lettuce crops and determine the current virus species present in lettuce, proximal weed species and beneficial pollinator field margin reservoirs and aphid vectors
  2. Molecular methods, including RT-PCR and long-read sequencing will be used to investigate the virome and characterise the diversity of virus species present
  3. A selected number of virus isolates will be screened in controlled field trials to quantify the impacts of virus infection on lettuce yield, shelf life and quality following infection at different stages of growth
  4. The Lactuca diversity set will be screened for resistance to TuYV

Short-term impacts include a greater understanding of the virus problems within UK lettuce crops. Determination of which growth stage is most affected by virus infection, effects on yield, quality and shelf-life and which aphid species are the most important vectors of viruses in lettuce. This will provide advice to growers about when they need to be protecting their crops from virus threats, modes of virus transmission and current options for control. 

Long-term impacts include sustaining UK lettuce production, through the reduction of both pre-harvest virus problems that impact quality and loss of a harvestable crop. Post-harvest virus issues that result in shorter storability due to reduced crop quality, will build resilience in our food system. 

The most potent and sustainable control and mitigation option for reducing losses due to virus infection is plant resistance. We have identified a number of sources of resistance to a number of viruses in a number of crops and identified the genes responsible for resistance. Some of these resistances appear to be very broad spectrum and potentially very durable. We work closely with plant breeding companies to ensure uptake and deployment of these resistances in commercial crops. Our identification of the genes responsible for the resistances has resulted in a dramatic acceleration of their introgression into commercial plant varieties by commercial seed companies. 

G’s Growers is a cooperative of growers, growing over 6,000 ha of high-quality fresh vegetables and salads in the UK. Production sites are based in Norfolk, Suffolk, Cambridgeshire, Kent, West Sussex and the West Midlands. G’s are a major lettuce producer in the UK and supply to all the major supermarkets. The successful candidate will be working closely with G’s to provide advice to growers about when they need to be protecting their crops from virus threats, modes of virus transmission and current options for control.


This PhD will be based at NIAB, Cambridge and registered with the University of Warwick.


Contact Charlotte Nellist or John Walsh for an informal discussion on the research content of this PhD.

Beginning in October 2023, the successful candidate should have (or expect to have) an Honours Degree (or equivalent) with a minimum of 2.1 in a degree that includes at least one of the following, Plant Science, Plant Genetics, Virology, Molecular Biology, Applied Statistics, or other related science subjects. Students with an appropriate Masters degree are particularly encouraged to apply.

We welcome UK, EU, and international applicants. Candidates whose first language is not English must provide evidence that their English language is sufficient to meet the specific demands of their study. Candidates should check the requirements for each host organization they are applying to, but IELTS 6.5 (with no component below 6.0) or equivalent is usually the minimum standard.

Anyone interested should complete the online application form before the deadline of 6th January 2023. Interviews will take place at the end of January/beginning of February 2023.

Please contact [Email Address Removed] for further application details.

Apply now

Funding Notes

This studentship is for four years and is fully funded in line with UKRI-BBSRC standard rates. These are:
An annual maintenance stipend of £17,668, fee support of £4,596, a research training support grant of £5,000 and conference and UK fieldwork expenses of £300.
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