Improvement of a diagnostic test to allow more precise localisationof tobacco rattle virus in fields

diagnostic-test-of-trv

Traditional bait tests take more than a month to complete and require vast resources. Targeted application with nematicide might be possible if the distribution of the virus were known using TaqMan technology.

Few satisfactory methods are available for the control of TRV infection. The current practice is to treat the whole field with nematicide should any TRV be identified. More targeted application might be possible if the distribution of the virus were accurately known. Existing methods of determining the occurrence of TRV rely either on counts of trichodorid numbers, which do not necessarily correlate with the presence of virus, or on detecting the virus in bait plants grown in samples of soil. Traditional bait tests take more than a month to complete, require large amounts of glasshouse space and are a significant cost to growers. A development of the bait test, now being offered through the Central Science Laboratory at York, uses real time quantitative polymerase chain reaction (TaqMan) technology to detect the virus in the roots of the bait plants. Another new diagnostic, developed at SCRI and available through SAC, uses improved nematode extraction systems and TaqMan technology to detect viruliferous nematodes.

Work undertaken for this project was based at three TRV infected sites in East Midlands (England), Angus and near Dundee (Scotland). All sites were growing cereal crops in 2004, which allowed easy weed sampling, and were planned for potato production in 2005. Weeds are in effect in situ bait plants that could be used as indicators of the presence of the virus. Work was therefore undertaken to compare the detection of TRV, using TaqMan technology, in the roots of weeds and of glasshouse-grown bait plants. Occurrence of virus would be mapped in detail within 2 ha sites using TaqMan molecular procedures both on the roots of weeds and (where applicable) of crop plants e.g. barley, and on conventional bait plants. In addition, the distribution of virus found in these tests was compared with the occurrence of spraing symptoms in a potato crop in the following year. Because nematodes and virus spread only gradually, mainly through soil movement (e.g. ploughing) or in the seed of a few weed species, knowledge of the distribution of TRV is likely to remain applicable for several years.

Project report: Independent variety trials

project-report-independent-variety-trials-2005

Varietal performance for susceptibility to blight, black dot, black scurf, silver scurf, skin spot, common scab, powdery scab, blackleg, dry rot, potato cyst nematodes and other damages

To comply with national and European Community legislation for marketing seed potatoes, varieties must be placed on the official National List (NL) of a Member State, which is then automatically entered on to the Common Catalogue (EC National List). Part of the NL testing involves assessing a new variety for Value for Cultivation or Use. In the UK, this testing is largely concentrated on assessing varietal performance for susceptibility to diseases, pests and important tuber quality characteristics.

This 28-page experimental report describes tests conducted on 4 varieties undergoing their 2nd year of UK NL testing, 7 varieties which had completed UK NL tests and 5 Common Catalogue varieties. The above varieties were tested against foliage late blight, black dot, black scurf, silver scurf and skin spot. The Common Catalogue varieties were also tested for susceptibility to common scab, powdery scab, blackleg, dry rot, potato cyst nematodes, external (splitting) and internal (bruising) damages. The report presents a comprehensive summary that covers Project Aims, Work Undertaken and Findings (results on Susceptibility/resistance for 2005 are summarised in a table and rated on 1 (Low) – 9 (High) for resistance to disease, pest and defects) and conclusions.