A polyvalent tool for detecting coguviruses in multiple hosts allowed the identification of a novel seed-transmitted coguvirus infecting Brassicaceae

The genus Coguvirus, a recently established genus in the family Phenuiviridae, includes several species whose members infect both woody or herbaceous hosts, suggesting broader host range and wider distribution than previously. To gain insights into the epidemiology and biology of coguviruses, a polyvalent reverse transcription-polymerase chain reaction (RT-PCR) assay using degenerate primers was developed. The specificity of the assay for coguviruses was confirmed by testing citrus and apple plants infected by previously reported coguviruses and/or several unrelated viruses. The expected 236-bp amplicon was obtained from citrus, apple, pear, watermelon and several species of the family Brassicaceae. Sequencing of the PCR amplicons allowed the identification, for the first time in Italy and/or Europe of several coguviruses in multiple hosts, confirming the effectiveness of the assay. Moreover, a new virus, tentatively named Brassica oleracea Torzella virus 1 (BoTV1), was detected in several plants of cabbage Torzella. The complete genome of BoTV1, determined by high-throughput sequencing and 5’ rapid amplification of cDNA ends (RACE), revealed that it has the typical molecular features of coguviruses and fulfils the current criteria to be classified as a member of a new species, for which the tentative name Coguvirus torzellae is proposed. The same polyvalent assay was also used to investigate and confirm that BoTV1 is transmitted through seeds in black cabbage, thus providing the first evidence on the relevance of this natural transmission mode in the epidemiology of coguviruses.