The complete sequence of a new wheat-infecting isolate of Wheat dwarf virus from Sweden (WDV-[Enk1]) was determined, as well as a 726-nt region covering part of rep and the long intergenic region (LIR) of six other wheat-infecting Swedish isolates and a barley-infecting isolate from Hungary (WDV-Bar[HU]). Analyses including these and previously published sequences showed that the wheat-infecting isolates of WDV displayed less than 3% of divergence. Most of the nucleotide changes were silent and the largest variation was detected in LIR. In contrast, the barley-infecting isolate was clearly different with 16% of sequence divergence compared to the wheat isolates. The WDV isolates infecting barley or wheat seem to represent two differentiated strains.

Four virus isolates were obtained in FRG and Sweden from sugarbeet roots which had become infected via the soil. All isolates had rod‐shaped particles of four or five different lengths. Serologically they were unrelated to beet necrotic yellow vein furovirus and several other viruses of a similar morphology including two serologically distinct sugarbeet isolates from California (US). Our isolates were, however, serologically related to beet soil‐borne furovirus which has been described in England. They could be subdivided into two serotypes.

Sequence determination of full-length cDNA clones of genomic segments 7-10 (S7-S10) of oat sterile dwarf fijivirus (OSDV) revealed that the 5h and 3h ends of the plus strands of these segments had the same conserved terminal sequences, 5h AACGAAAAA and UUUUUUUAGUC 3h. These sequences are similar, but not identical, to the conserved terminal nucleotide sequences of the genomic segments of rice black streaked dwarf fijivirus (RBSDV) and maize rough dwarf fijivirus (MRDV). The coding strands of S7 and S10 each contained two large nonoverlapping open reading frames (ORFs), as do RBSDV S7 and S9, MRDV S6 and S8 and Nilaparvata lugens reovirus (NLRV ; a putative member of Fiji-

No abstract

Some experiments with soil‐borne beet viruses in cement tubes in a wire netting enclosure are described. It is confirmed that rhizomania (virus + vector) originating from German soil can survive and cause rhizomania in Sweden. Antisera produced in 1987 to one German BNYVV isolate and to one Swedish soil‐borne beet virus isolate, 86‐109, which is distinct from BNYVV, were used to check ELISA reactions in the tube beets. Positive ELISA was obtained not only for BNYVV but also for the 86‐109 virus from tubes with German inoculum. Beets from tubes with Swedish inoculum reacted only against 86‐109 antiserum. In 1988‐09, ELISA of 118 sugarbeet plants from Öland and 73 from Skåne, collected in 42 different fields with spots resembling rhizomania, showed no or weak reactions against 86‐109 antiserum, in contrast to plants collected in 1987. However, after transplanting the field plants into a warm glasshouse and using bait plants it was shown in ELISA and in transmission to Chenopodium quinoa that many of the bait plants became infected with the 86‐109 and ‘related viruses’ but not with BNYVV. Viruses of the 86‐109 type seem to be common both in Sweden and elsewhere but may escape detection, especially in mixed infections with BNYVV.