title: Identification and molecular characterization of two naturally occurring Soybean mosaic virus isolates that are closely related but differ in their ability to overcome Rsv4 resistance.
abstract: A naturally occurring Rsv4 resistance-breaking isolate (L-RB) and a closely related non-resistance-breaking isolate (L) of Soybean mosaic virus (SMV) were identified in soybean fields in London, Ontario, Canada. The viral genomes of L and L-RB were completely sequenced. Each isolate has a 9585-nucleotide genome with a single open reading frame encoding a polyprotein of approximately 350 kDa. L-RB and L have a very high sequence similarity (99.6%) at both the nucleotide and amino acid levels. Phylogenetic analysis showed that the two isolates belong to the G2 pathotype. Pathogenicity predictions of all virus/soybean combinations, based on the phylogenetic profile, were confirmed by pathogenicity tests using L and L-RB isolates and soybeans carrying different resistance genes, with an exception that L-RB infected a soybean cultivar carrying Rsv4 resistance. The temporal and spatial proximity of L and L-RB and their high sequence similarity suggest L-RB was likely derived from the SMV-L quasispecies. Recombination analysis did not reveal the evidence of genetic recombination for the emergence of L-RB. Mutations introduced by virus-encoded RNA-dependent RNA polymerase during viral genome replication and selection pressure probably contributed to the occurrence of L-RB.
authors.affiliation: Southern Crop Protection and Food Research Centre, Agriculture and Agri-Food Canada, 1391 Sandford Street, London, Ontario, Canada N5V 4T3.
authors.forename: Alla G
authors.initials: AG
authors.lastname: Gagarinova
authors.forename: Mohan
authors.initials: M
authors.lastname: Babu
authors.forename: Vaino
authors.initials: V
authors.lastname: Poysa
authors.forename: John H
authors.initials: JH
authors.lastname: Hill
authors.forename: Aiming
authors.initials: A
authors.lastname: Wang
mesh_terms: D016679:Genome, Viral; D007113:Immunity, Innate; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology / Q000821:virology*; D010940:Plant Proteins / Q000235:genetics / Q000276:immunology*; D017800:Potyvirus / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification* / Q000472:pathogenicity; D013025:Glycine max / Q000235:genetics / Q000276:immunology / Q000821:virology*
chemical_list: D010940:Plant Proteins