Badnaviruses Of Sweetpotato: Symptomless Co-Inhabitants On A Global Scale

Abstract

Sweetpotato is among the most important root-crops worldwide, particularly in developing countries, and its production is affected severely by a variety of virus diseases. During the last decade a number of new viruses have been discovered in sweetpotatoes from different continents through next generation sequencing studies, among them belonging to the genus Badnavirus and collectively assigned to the species Sweet potato pakkakuy virus (SPPV). We determined the complete genome sequence of two SPPV isolates and show the ubiquitous presence of similar viruses in germplasm and field material from around the globe. We show SPPV is not integrated into the sweetpotato genome, occurs only at extremely low titers but is nevertheless efficiently transmitted through seeds and cuttings. They are unaffected by virus elimination therapy and lack any discernible symptoms in sweetpotatoes or indicator host plants. Nevertheless, they show considerable variation in their nucleotide sequences and correspond to several genetic lineages. Studies of their interaction with the two most important sweetpotato viruses showed only limited synergistic increase in the titres of one of two SPPV isolates. We contend that these viruses may pose little threat to sweetpotato production and more likely represent a new type of persistent virus in a possibly commensal or mutualistic relationship with sweetpotato.\n\nImportanceNext generation sequencing approaches have in the last few years led to the discovery of many virus like sequences in different crop plants including sweetpotatoes. The significance of such discoveries can sometimes be elusive when they have not been associated with specific symptoms due to mixed infections or have been found in apparently healthy plants. Badnavirus sequences found in sweetpotatoes provide a typical case. Considering they have now been reported globally, it was important to determine how common these viruses are and what their possible impact may be on sweetpotato production. The significance of our research lies in resolving the case of badnaviruses, providing evidence they represent a new type of vertically transmitted persistent and apparently harmless episomal viruses living in a state of commensalism with their host.