Aphid and virus: potatoes
The main virus species in GB potato crops is currently Potato Virus Y (PVY).
Primary infection occurs in the growing season and is aphid-borne. Secondary infection is tuber-borne.
One of the major threats to the health of seed potato crops is the transmission of viruses by aphids. The viruses may be persistent (e.g. Potato Leaf Roll Virus; PLRV) or non-persistent (e.g. potyviruses such as PVY, PVA). This distinction is important in determining how long it takes an aphid to acquire the virus from an infected host plant and transmit it on to another plant. This in turn has an impact on which aphids can transmit the virus and how to manage them using insecticides or other means.
AHDB has various tools and resources to help you monitor and manage aphids.
Virus detection/test methods
There are two main methods of post-harvest testing for the presence of virus in potato tubers. The standard growing on ELISA test and the molecular methods which uses real-time PCR (often referred to Q-PCR).
Standard Growing On test (GO)
Potato tubers are prepared and treated with gibberellic acid which promotes the break of dormancy and induces sprouting. These samples are planted out and leaf samples are taken 5 – 6 weeks after planting. The leaf tissues are tested using the ELISA method which uses antibodies which are specific to certain groups of viruses.
Direct Tuber Testing (DTT)
DTT uses molecular real-time polymerase chain reaction (PCR) methods which detect the presence of virus nucleic acid within the tuber sample.
Other differences between the two tests are mainly cost and turnaround time. The standard growing on test requires more handling and plant growth time (usually between 4 – 6 weeks) but is slightly more cost effective. The molecular method is more expensive but the advantage here is a faster turnaround time usually within days.
The two tests use different tissues from different parts of the tuber and so there will be variability related to virus distribution in the dormant tuber, especially in tubers from plants infected late during the growing season (late primary infections). Overall, they should give comparable results, while each testing laboratory might have different sampling strategies. However, it is important to note that both methods have the caveat of being dependent on the distribution of the virus within the tuber (especially during primary infection) and also the type of sampling methodology used.
Testing laboratories have performed validation data usually following published guidelines (a requirement for ISO17025 accredited laboratories!) to ensure that these tests are “fit-for-purpose” and reliable.
Based on current information it is thought that growing-on and direct tuber testing qPCR are relatively comparable when they have been done side by side throughout the off-season. Some data suggest that early on in the post-harvest period, virus detection might be more efficient using a rapid direct tuber test, than in a standard growing on test.
Where can I get tubers virus tested?
Scottish Aphid Borne Virus Working Group: recommendations for 2021
The working group is a consortium of Scottish researchers with an interest in virus, representatives come from: SRUC, Scottish Agronomy Ltd, SASA, The James Hutton Institute, AHDB and McCain.
Recommendations are updated periodically based on the latest research and information as it becomes available. The latest update was made in May 2021.
Long-term (56 years in 2020) aphid data (from the suction-trap network) and weather data (Met Office and others) is used to forecast the date of the first aphid flights, as well as aphid abundance in spring and early summer.
You can sign up to be alerted to the first Peach Potato Aphid (Myzus persicae) found in a region/s, and also when the index value in a region exceeds a given threshold (you have a choice of three thresholds). You can select the locations of traps you want to monitor by choosing from up to eight regions.