Development and deployment of genotype-specific LAMP assays for monitoring Pepino mosaic virus (PepMV) in tomato

Project summary:

Pepino mosaic virus (PepMV) is one of the most economically important disease of tomatoes in the UK.  In 2013 and again in 2014, crops of Piccolo on several nurseries were severely affected with 3-4 and occasionally more trusses of fruit affected, resulting in substantial financial losses.  Symptom severity in the same variety can vary greatly on different nurseries, raising the question of possible mixed genotype infections.  Efforts to exclude the virus from a nursery and prevent persistence between successive crops by strict hygiene measures have had limited success.  LAMP assays that can discriminate CH2, EU and US1 genotypes of PepMV were recently published.  The aim of this joint ADAS/University of Nottingham/Fera proposal is to establish the LAMP assays in the UK so that rapid on-site testing of tomato plants for three different genotypes of PepMV is possible.  The assays will then be used to: i) investigate occurrence of mixed-genotype infections in crops, especially any with severe symptoms; ii) investigate efficacy of hygiene measures after crop removal in removing PepMV from glasshouse structures and equipment; iii) determine survival in tomato roots in soil and in composted tomato waste; iv) if mild strain CH2 is permitted for use in the UK, determine the spread of mild strain through a crop after inoculation, and check for other genotypes.  A method for rapid detection of PepMV in water will be examined.  If required, and especially for any crops with severe symptoms, samples could also be tested for other virus diseases.

Benefits to industry:

• Availability of a new tool to increase understanding of the current most important and widespread disease of tomato in the UK
• Knowledge on which PepMV genotypes are currently present in UK tomato crops
• Potential explanation of why the same variety can show more severe symptoms on one nursery than another
• Potential identification of locations where PepMV is persisting on nurseries after crop removal, thereby permitting revision of crop-hygiene protocols to address ineffective treatments
• Increased confidence that after inoculation with a commercially available mild strain a high proportion of plants rapidly become infected by the mild strain, and are protected from severe symptoms from other strains of the same genotype(s).
• Potential to check samples with severe symptoms for some other virus diseases of tomato.

Aims and objectives:

Project aim:

To increase understanding of PepMV symptom severity, persistence on nurseries and mild strain cross-protection.

Project objective:

1. To validate published LAMP assays for rapid detection of CH2, EU and US1 strains of PepMV;
2. To determine occurrence of mixed genotype PepMV infections in tomato crops;
3. To monitor greenhouse structures and equipment for occurrence of PepMV after crop removal;
4. To determine survival in tomato roots in soil and in composted tomato waste;
5. To validate a method for detection of PepMV in water and test some water samples from UK tomato nurseries;
6. To monitor spread of mild-strain CH2 PepMV and check for other genotypes in crops inoculated with mild-strain for cross-protection;
7. To communicate results to growers.