Ten Japanese field isolates of beet necrotic yellow vein virus (BNYVV) were transmitted to Tetragonia expansa by inoculation with sap from rootlets of sugar-beet seedlings, to which the virus had been transmitted by the fungus Polymyxa betae. RNA extracted from BNYVV particles obtained from the T. expansa leaves was analysed by agarose gel electrophoresis. Some isolates contained RNA-1 (7.1 kb), RNA-2 (4.8 kb), RNA-3 (1.85 kb) and RNA-4 (1.5 kb) and the others contained, in addition, RNA-5 (1.4 kb). Further isolates, derived from single lesions produced by these isolates, had a variety of RNA compositions. Some contained only RNA-I and RNA-2. Others contained, in addition, RNA-3, RNA-4, RNA-5 or RNA-6 (1.0 kb), or combinations of two or three of these components. Such isolates generally maintained their RNA composition on further subculture, and their particles had length distributions corresponding to their RNA components. Isolates containing RNA-I + 2 + 3 caused yellow or strongly chlorotic local lesions in T. expansa, Beta vulgaris, B. macrocarpa and Chenopodium quinoa, and caused systemic stunting and yellow mosaic in B. macrocarpa and, occasionally, in B. vulgaris. In contrast, isolates containing RNA-1 + 2 + 4 or 1 + 2 + 5 induced chlorotic lesions, those containing RNA-1 + 2 + 6 or 1 + 2 induced faint chlorotic lesions, and none of these isolates easily infected B. macrocarpa systemically. Isolates containing different combinations of RNA-3,-4 and -5 induced more severe symptoms than those containing a single RNA. Such synergistic effects occurred between RNA-3 and RNA-4 or RNA-5, or between RNA-4 and RNA-5 or RNA-6, but not between RNA-3 and RNA-6, or between RNA-5 and RNA-6. These small RNA species therefore contain the genetic determinant(s) for lesion type and for ability to infect B. vulgaris and B. macrocarpa systemically. RNA-1 and RNA-2 are viral genome components. The other RNA components have some characteristics of viral satellite nucleic acids but they may not all be dispensable if the BNYVV isolates are to survive in nature.

About half of Japanese isolates of beet necrotic yellow vein virus (BNYVV) were found to contain RNA 5 molecules, which were also detected in virus isolates from China and France. Sequence comparisons of RNA 5 (nucleotides 327 to 1171) in 25 isolates showed that there are up to 8% sequence differences, and that RNA 5 variants fall into three groups: group I contains most of the Japanese and Chinese isolates, group II two Japanese isolates, and group III four French isolates. The group I isolates fall into three small clusters. In the 26 kDa coding region of RNA 5, there was a maximum of 1.5% nucleotide sequence differences (6 amino acid changes) within the group and 8.4% nucleotide sequence differences (17 amino acid changes) between the groups. Comparisons of the coat protein gene of RNA 2 revealed that most of the Japanese and Chinese isolates belonged to the A type strain, but some isolates were of the B type. The French isolates (P type) were closely related to those of the A type. Mixed infections of the two types of virus and the two groups of RNA 5 were detected in a small area of Hokkaido. BNYVV might have been introduced into Japan and China by a similar route from at least two origins. These results, together with other evidence, suggest that the three groups of RNA 5 variants separated from an original population a long time ago and, thereafter, the group I population diverged further into three clusters, which may have been associated with the A type strain rather than the B type.

A Japanese man suffered from acute respiratory tract infection after returning to Japan from Bali, Indonesia in 2007. Miyazaki-Bali/2007, a strain of the species of Nelson Bay orthoreovirus, was isolated from the patient's throat swab using Vero cells, in which syncytium formation was observed. This is the sixth report describing a patient with respiratory tract infection caused by an orthoreovirus classified to the species of Nelson Bay orthoreovirus. Given the possibility that all of the patients were infected in Malaysia and Indonesia, prospective surveillance on orthoreovirus infections should be carried out in Southeast Asia. Furthermore, contact surveillance study suggests that the risk of human-to-human infection of the species of Nelson Bay orthoreovirus would seem to be low.

Two mutant strains of beet necrotic yellow vein virus (BNYVV) containing deletions in RNA 3 were obtained by single lesion transfers in Tetragonia expansa. The deleted regions encode either 94 or 121 amino acids toward the C-terminal part of the 25-kDa protein (P25). Wild-type and mutant virus strains were inoculated by Polymyxa betae to sugar beet seedlings of susceptible and partially resistant cultivars. No differences were found in virus content in rootlets between mutant and wild-type viruses or between susceptible and resistant cultivars after culture for 4 weeks in a growth cabinet. However, when virus-inoculated seedlings were grown in the field for 5 months, the wild-type virus caused typical rhizomania root symptoms (69 to 96% yield loss) in susceptible cultivars, but no symptoms (23% loss) developed in most plants of the resistant cultivar, and BNYVV concentrations in the roots were 10 to 20x lower in these plants than in susceptible plants. In contrast, the mutant strains caused no symptoms in susceptible or resistant cultivars, and the virus content of roots was much lower in both cultivars than in wild-type virus infections. Wild-type RNA 3 was not detectable in most of the taproots of a resistant cultivar without any symptoms, suggesting that replication of undeleted RNA 3 was inhibited. These results indicate that the P25 of BNYVV RNA 3 is essential for the development of rhizomania symptoms in susceptible cultivars and suggest that it may fail to facilitate virus translocation from rootlets to taproots in the partially resistant cultivar.

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