Partial characterization of two aphid-transmitted viruses associated with yellow leafspot of Spiraea

Two previously undescribed viruses were associated with a yellow leafspot disease of spiraea (Spiraea spp.) in the midwestern USA. The first virus, named spiraea leafspot virus (SLSV), is a badnavirus which has a 7.4 kb dsDNA genome and resembles other badnaviruses in particle and genome properties, but is unusual in being transmitted by an aphid (Aphis spiraecola) rather than by mealybugs. The second virus, which is also transmitted by A. spiraecola, has spherical 30-35 nm particles containing a 7.2 kb ds RNA genome. This virus was named spiraea leafspot spherical virus (SLSSV). In particle morphology and genome type SLSSV resembles some members of the family Totiviridae, none of which have been reported to infect plants or higher organisms. In the majority of cases SLSV and SLSSV occurred in mixed infections. Early-season symptoms were associated with the presence of SLSSV and absence of SLSV, whereas late-season symptoms were associated with the presence of SLSV and absence or greatly reduced levels of SLSSV.