Elucidation of the Nature of Pelargonium Vein Banding Virus Sequences Present in Pelargonium × hortorum

The family Caulimoviridae are plant-infecting pararetroviruses that replicate by reverse transcription and encapsidate a circular dsDNA genome. They can occur as episomal (encapsidated and replicative forms), and endogenous forms integrated into the host genome. Some endogenous sequences can give rise to episomal forms. In this study, we report and characterize a new badnavirus infecting Pelargonium × hortorum. We propose the name Pelargonium vein banding virus (PVBV). The episomal genome is 7,586 bp in length. Endogenous PVBV (ePVBV) DNA was identified in healthy plants and characterized. Southern blotting and PCR suggest that in many cultivars the ePVBV consists of a tandem array of the complete PVBV genome. The ePVBV tandem array was not detected in ‘Maverick White’. The major parents of Pelargonium × hortorum hybrids are P. zonale and P. inquinans. P. zonale contained ePVBV but P. inquinans did not. The sequence of ePVBV recovered from the cultivar ‘BullsEye Salmon’ was >99% identical to the episomal sequence. Agroinoculation experiments demonstrated that ePVBV is infectious. Bacilliform-shaped virions with a modal particle length of 144 nm and 33 nm in diameter were recovered from leaves of agroinfected ‘Maverick White’ exhibiting mosaic symptoms and chlorosis surrounding the veins. P. zonale and Pelargonium × hortorum varieties with full ePVBV genomes were not infected. Interestingly, P. inquinans, which does not contain ePVBV was also not infected.