Global phylogenetic analysis of soybean dwarf virus isolates and their associations with aphid vectors and severe disease in soybeans.

Soybean dwarf virus (SbDV) was first described in Japan as an agent of severe soybean disease transmitted by the foxglove aphid, Aulacorthum solani, with separable yellowing (Y) and dwarfing (D) strains. SbDV of both Y and D genotypes were later documented in other countries. For three decades, SbDV isolates were assessed to evaluate risk to U.S. soybean production. U.S. SbDV isolates were transmitted by the pea aphid Acyrthosiphum pisum and showed limited disease in soybeans, suggesting it was not a major threat to U.S. soybean production. Here we report 21 new full-length SbDV genome sequences including those of the originally described Japanese Y and D isolates, isolates from Syria and New Zealand associated with severe disease, and 17 isolates from U.S. field collections. Using these new full-length genomes, a global phylogeny was assembled and used to revisit risk assessment based on sequence similarities, isolate pathogenicity, and vector specificity.

A previously undescribed potyvirus isolated and characterized from arborescent Brugmansia.

A suspected virus disease was identified from an arborescent Brugmansia x candida Pers. (syn. Datura candida Pers.) tree. The causal agent was aphid transmissible at low rates. Viral particles were purified from infected tobacco tissue, analyzed, and purified virions were inoculated into healthy tobacco plants to recreate the symptoms. The virions had a mean length of 720-729 nm, and infected cells contained inclusion bodies typical of potyvirus infections. Analysis of infected tissues and purified virions with a panel of potyvirus-specific antibodies confirmed identification as a potyvirus. Viral host range, dilution end point, thermal tolerance and aphid transmission characteristics were examined. The viral genome (9761 nt) is typical of potyviruses, with the closest related potyvirus being pepper mottle virus, at 72 % nt sequence identity. Based on conventions for naming novel potyviruses, the virus was determined to be a member of a previously undescribed species, tentatively named "Brugmansia mosaic virus" (BruMV).

Molecular analysis of soybean dwarf virus isolates in the eastern United States confirms the presence of both D and Y strains and provides evidence of mixed infections and recombination.

Soybean dwarf virus (SbDV), first identified as an agricultural problem in Japan, has emerged as a growing problem in the Midwestern United States. The majority of research on SbDV had been limited to four lab maintained strains from Japan. SbDV had been found in clover in the eastern United States, but these isolates rarely emerged into soybeans. These isolates were analyzed by multiplex PCR and sequencing, revealing that some were infections of both Y and D components, including a recombinant subisolate. Phylogenetic analyses for the US isolates revealed a broad diversity of SbDV, with selection pressure greater on the movement protein than the coat protein. The field isolates from the Eastern United States showed differences in symptoms, aphid transmission and host range, demonstrating that a study of field isolates is an important complement to laboratory maintained strains in understanding the biology and evolution of plant viruses.