Identification and characterization of plant pararetrovirus from Pelargonium x hortorum cultivars and Gemycircularvirus from Euonymus alatus

Abstract

Ornamental crops have high economic importance and are popular worldwide; they are cultivated as potted flowering plants, cut flowers, foliage plants, herbaceous perennials, annual bedding, garden plants, and propagative floriculture materials. In the United States of America (USA), ornamental crops had a total sale value of $6.43 billion for 2021 (USDA, NASS, 2022). Largely ornamental plant species are propagated vegetatively, thus contributing to the uncontrolled transmission of viruses when plant materials are not being tested. DNA viruses are widely spread in the ornamental plant species of economic importance. Caulimoviridae are called plant-pararetroviruses, which means they replicate by reverse transcription and the encapsidated genome is DNA. DNA from some members is also integrated into the host genome, which makes virus detection difficult. Detection of viruses is a crucial step in virus disease management since no direct means of control of viral diseases are readily available. This research aimed to identify and characterize two new DNA viruses from ornamental crops, Pelargonium x hortorum hybrids and Burning bush (Euonymus alatus). In these studies, a new badnavirus infecting pelargonium was reported and proposed with the name Pelargonium vein banding virus (PVBV). The encapsidated (episomal) genome of PVBV was sequenced and deposited into NCBI under accession number NC_013262. Endogenous PVBV DNA (ePVBV) was identified and investigated using PCR and Southern blotting. The complete genome sequence of ePVBV was recovered from the Pelargonium x hortorum cultivar Bullseye Salmon (BES) and found to be >99 % identical to the episomal form. ePVBV was integrated into one of the parents, Pelargonium zonale, of the interspecies hybrid Pelargonium x hortorum. The complete genome sequence of Euonymus-associated Gemycircularvirus from Euonymus alatus is also reported. In addition, infectious constructs of PVBV and Euonymus-associated Gemycircularvirus were designed, constructed and inoculated into Pelargonium cultivars and Nicotiana benthamina plants, respectively. Altogether, these results are helpful for plant disease diagnosticians, pathologists, and breeders.