Preliminary investigations of an uncharacterized virus of winter wheat (Triticum aestivum L.) in England

In 1995 and each subsequent year, the symptoms of an unrecognized disease have been recorded in a crop of winter wheat (cv. 'Riband') in Bedfordshire, England. Leaves of affected plants initially show faint mosaic symptoms which appear in April and develop into a more extensive chlorotic streaking during May and June. The disease appears to be restricted to discrete areas in the field which have changed little in size or position. Measurements made by comparing diseased and symptomless plants in 1996 showed that the yield of affected plants was reduced by 24 %. Electron microscopy revealed that the disease symptoms are associated with the presence of a rod-shaped virus which resembles soilborne wheat mosaic virus (BWMV). The particles are 18-20 nm in width and have modal lengths of 100, 220 or 300 nm suggesting that the virus is multipartite. The vector of the disease is unknown but the virus can be transmitted in air-dried soil suggesting that a fungal vector may be involved. Also in common with SBWMV, the virus can be transmitted by seed and is nor readily transmitted mechanically. Despite these similarities, extensive tests using seven different serological assays which detect all reported SBWMV isolates did not unequivocally identify this virus. Similarly, RT-PCR using primers developed against both RNA 1 and 2 of the type strain of SBWMV did not amplify the expected product. However, the unidentified virus does not resemble any other known virus of wheat and therefore it is thought that it represents either an unreported. strain of SBWMV or a new wheat virus.