DIRECT DETECTION OF TRANSCAPSIDATED BARLEY YELLOW DWARF LUTEOVIRUSES IN DOUBLY INFECTED PLANTS

A novel immunohybridization assay was used to analyse the virion capsid proteins and nucleic acids of various barley yellow dwarf luteoviruses from singly and doubly infected plants. Plants singly infected with New York MAV or RPV contained only viruses indistinguishable from the parental types, but plants doubly infected with these viruses contained transcapsidated virions (MAV RNA in RPV protein capsids). The presence of transcapsidated virions was positively correlated with altered aphid transmission characteristics of MAV from the same plants. Virions with phenotypically mixed capsids (chimeric capsids containing subunits from both co-infecting viruses) were not detected in these plants using heterologous and homologous ELISAs. Transcapsidated virions were detected in mixed infectious of California and New York MAV and RPV isolates and, more epidemiologically significantly, in natural doubly infected field plants. In addition, evidence for two-way transcapsidation was obtained using immunohybridization and aphid transmission studies from mixed infections of New York RPV and PAV isolates.