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. Tuber-borne disease is an important route for infection and hence a combination of leaf-testing in the mother crop and tuber testing will be appropriate for many seed potato crops.
NIAB offers both the standard grow-on ELISA test and the rapid PCR test for the presence of virus in potato tubers. Both approaches can be used to assess PLRV and PVY. Overall, both methods have been shown to give comparable results, but some differences may occur, especially in tubers from plants infected late during the growing season (late primary infections).
In the standard grow-on ELISA test, potato tubers are prepared, eye samples taken and treated with gibberellic acid which promotes the break of dormancy and induces sprouting. The samples are grown in the glasshouse and leaf samples are taken 4–6 weeks after planting when there is sufficient leaf material available. The leaf tissues are tested using the ELISA method which uses antibodies which are specific to each virus.
The most common assessment is for PLRV and PVY. Additional assessments of PVX, PVS, PVA, PVV and PVYn strain can also be made. The same ELISA test is also used for leaf samples submitted in-season. The standard grow-on test requires handling and plant growth time, therefore the total duration of the test can be up to 8 weeks.
In the rapid assessment, NIAB uses molecular methods which uses real-time PCR (often referred to Q-PCR). The molecular method is more expensive but the advantage is a faster turnaround time usually within days. Direct tuber testing uses PCR methods to detect the presence of virus nucleic acid within the tuber sample. The total duration of the test is commonly about one week.
For both tests, the incidence of virus infection (% tubers affected) is estimated for the seed stock and reported. NIAB recommends a sample size of 110 tubers for routine virus testing. If customers have any bespoke requirements, discuss them with the team in advance by contacting Helen Appleyard.