Heterologous encapsidation in mixed infections among four isolates of barley yellow dwarf virus

We used immunohybridization and ELISA to investigate heterologous encapsidation (transcapsidation and phenotypic mixing) between paired isolates of barley yellow dwarf virus (BYDV) in doubly infected oat plants, Avena sativa L. cv. Clintland 64. Virons in samples extracted from plants doubly infected with two viruses were trapped with an antibody specific to one virus, and the nucleic acids of the trapped virions were identified with a cDNA probe specific to the other. Heterologous encapsidation was found in mixed infections between isolates NY-RPV and NY-MAV-PS1, NY-RPV and P-PAV, NY-RMV and NY-MAV-PS1, P-PAV and NY-MAV-PS1, and NY-RPV and NY-RMV. Heterologous encapsidation between NY-RPV and P-PAV, and between NY-RPV and NY-MAV-PS1, occurred in one direction, while the heterologous encapsidation between P-PAV and NY-MAV-PS1 occurred in both directions. Further analysis by heterologous ELISA and immunohybridization assays with immunoprecipitated samples demonstrated that transcapsidation was the predominant type of heterologous encapsidation in mixed infections of NY-RPV and P-PAV, NY-RPV and NY-MAV-PS1, and NY-RMV and NY-MAV-PS1; phenotypic mixing was the predominant type of heterologous encapsidation in mixed infections of P-PAV and NY-MAV-PS1. Phenotypic mixing was also detected in mixed infections of NY-RPV and NY-RMV. These results suggest that among BYDV isolates transcapsidation is more common between distantly related isolates than between more closely related isolates, and phenotypic mixing is more common between more closely related isolates than distantly related isolates.