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 h ave been recorded in a crop of winter wheat (cv. 'Riband') in Bedfordshire, England. Leaves of affected plants initially show faint mosaic symptoms wh ich appear in April and develop into a more extensive chlorotic streaking d uring May and June. The disease appears to be restricted to discrete areas in the field which have changed little in size or position. Measurements ma de by comparing diseased and symptomless plants in 1996 showed that the yie ld of affected plants was reduced by 24 %. Electron microscopy revealed tha t the disease symptoms are associated with the presence of a rod-shaped vir us which resembles soilborne wheat mosaic virus (BWMV). The particles are 1 8-20 nm in width and have modal lengths of 100, 220 or 300 nm suggesting th at 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 similariti es, extensive tests using seven different serological assays which detect a ll reported SBWMV isolates did not unequivocally identify this virus. Simil arly, RT-PCR using primers developed against both RNA 1 and 2 of the type s train of SBWMV did not amplify the expected product. However, the unidentif ied 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 n ew wheat virus.