Rose viruses: Understanding the current status and protecting the future of the UK rose sector

Abstract

The rose (Rosa spp.) is the national flower of England and one of the most valued ornamental flowering shrubs grown around the globe. Despite the spread of rose viruses and their importance in rose cultivation, they have not been studied in detail in the United Kingdom (UK) since the 1980s. Molecular methods have evolved since then, and as a result they have rarely been deployed to study these viruses. In the UK many viruses have been reported previously infecting roses such as arabis mosaic virus (genus Nepovirus) and strawberry latent ringspot virus (family Secoviridae). However, numerous viruses have been identified infecting roses in recent years, especially with the application of high-throughput sequencing (HTS). Diagnosis is fundamental to facilitate the management of plant diseases, and early detection is essential for successful biosecurity campaigns, for example against rose rosette virus (RRV; genus Emaravirus), which is devastating roses in the USA and Canada, and was recently discovered in India (2017). In this project, different molecular (PCR, qPCR and HTS) and serological methods (ELISA) have been used to understand the baseline of viruses present in roses in the UK. Detailed experiments were performed to compare various targeted and non-targeted methods, including two different pipelines for HTS data analysis, Angua and EDNA. RT-qPCR showed the highest sensitivity for the detection of known viruses, whereas ELISA was identified as the technique with the lowest sensitivity. The Angua and the EDNA pipelines showed non-significant differences in sensitivity from RT-qPCR except in the detection of viral agents with lower titre. The advantages of HTS as a potential future front-line diagnostic tool are described. The performance of this study has allowed the estimation of the prevalence of some previously reported viruses in the UK but also the identification of Rosa spp. as a new host for viruses that are widespread in the country. This work resulted in three first virus records in the UK (rose cryptic virus-1, rose spring dwarf virus, and sweetbriar rose curly top virus), and the discovery of a new virus species (rosa ilarvirus-1; genus Ilarvirus). Furthermore, this research has proven a connection between the movement of plant pathogens and the trade in roses as cut flowers.