|SPORE Bulletin of the CTA No. 44 (CTA Spore, 1993, 16 p.)|
The identification, characterization and handling of viruses and other pathogens that can present problems in plant disease diagnosis, such as mycoplasma-like organisms and fastidious bacteria, requires more trained personnel and specialised equipment than is usually available in tropical countries.
The Tropical Virus Unit (TVU) at the Institute of Arable Crops Research, Rothamsted Experimental Station, in the UK offers help with the diagnosis of such infective agents. This facility complements other diagnostic services for fungi and bacteria such as those offered by CAB International's International Mycological Institute. The TVU is supported by the Natural Resources and Environment Division of Britain's Overseas Development Administration.
When potentially diseased plant samples are received they are examined by electron microscopy and, where possible, serological methods are used to help identify the causal agent(s). Other methods, such as nucleic acid hybridization and DNA amplification, are also increasingly used. Once the agent is identified guidance on its method of transmission and spread can be given which may assist the study of its epidemiology and control.
Whilst the TVU receives, and welcomes, unsolicited samples, the unit prefers users of the service to write first and appraise them of their problem. TVU can then advise on the best method of sending samples and provide permits to allow passage through UK Plant Health and Quarantine barriers.
Some contacts are brief and can take a day or two from receipt of samples to despatch of answer. Most are more prolonged, with several samples being sent, and there may be correspondence about the problem. Sometimes the scope and importance of the problem indicates the need for a more comprehensive project. Funding can then be jointly sought from suitable donor agencies.
The following example illustrates the work of the TVU. Many years ago the Caribbean Agricultural Research and Development Institute (CARDI) was asked to produce seed of West Indian hot peppers that would be of high quality and free of virus contamination. After an initial market survey to determine which varietal characteristics were required, CARDI chose a red lantern type and the yellow Scotch Bonnet. Plots were grown at Betty's Hope Field Station, Antigua, which was isolated from other pepper crops. In spite of precautions, virus symptoms increased and seed production was halted in 1970. The TVU subsequently became involved and was able to identify two viruses, one of which (pepper mild mottle tobamovirus) was transmitted through the seed. Antiserum to the virus was produced and a simple serological test devised for both plants and seed. Because the virus is carried on the seed coat, seed is now treated before distribution to destroy the virus.
Training and technology transfer also play a significant part in the activities of the unit. Courses in basic plant virology have been given overseas and postgraduate students working with the TVU can pursue higher degrees through Rothamsted's associated links with UK universities.
Tropical Virus Unit
Rothamsted Experimental Station
Hertfordshire AL5 2JQ, UK