Viruses transmitted by nematodes1

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Abstract
The transmission of plant viruses by nematodes is remarkable in involving only two distinct groups of viruses, nepo viruses and tobraviruses, and being limited to longidorid, Paratrichodorus and Trichodorus nematodes respectively. Tobraviruses and their associated vector nematodes are not discussed here. Only 11 of the 36 described nepoviruses are transmitted by nematodes, and 6 of these 11 viruses are present in Europe naturally associated with 8 virus‐vector longidorids. Specific relationships exist between the serologically distinct viruses and their vector nematode species. Specificity is largely determined by the virus coat protein and by an inherited ability of the nematode to retain virus particles at specific sites within its oesophagus. This specific relationship can be quite subtle, extending to populations of vector nematodes and also to virus isolates which apparently are serologically indistinguishable. Several serological and/or symptomatological variants of nepoviruses may be present at a field site in association with one or more vector nematode species. The exposure of different crops and new cultivars to these virus and vector combinations will probably result in the occurrence of further nematode‐transmitted virus diseases. New methods for suppressing damage to crops caused by these diseases are required including the likely use of transgenic resistant cultivars.