Comparison of Illumina de novo assembled and Sanger sequenced viral genomes: A case study for RNA viruses recovered from the plant pathogenic fungus Sclerotinia sclerotiorum

• Illumina sequencing yielded nine full mycoviruses genomes from Sclerotinia sclerotiorum.
• De novo assembled genomes from Illumina were >99.3% similar to Sanger sequencing.
• The viruses included five novel mitoviruses, a novel hypovirus and a novel endornavirus.

The advent of ‘next generation sequencing’ (NGS) technologies has led to the discovery of many novel mycoviruses, the majority of which are sufficiently different from previously sequenced viruses that there is no appropriate reference sequence on which to base the sequence assembly. Although many new genome sequences are generated by NGS, confirmation of the sequence by Sanger sequencing is still essential for formal classification by the International Committee for the Taxonomy of Viruses (ICTV), although this is currently under review. To empirically test the validity of de novo assembled mycovirus genomes from dsRNA extracts, we compared the results from Illumina sequencing with those from random cloning plus targeted PCR coupled with Sanger sequencing for viruses from five Sclerotinia sclerotiorum isolates. Through Sanger sequencing we detected nine viral genomes while through Illumina sequencing we detected the same nine viruses plus one additional virus from the same samples. Critically, the Illumina derived sequences share >99.3 % identity to those obtained by cloning and Sanger sequencing. Although, there is scope for errors in de novo assembled viral genomes, our results demonstrate that by maximising the proportion of viral sequence in the data and using sufficiently rigorous quality controls, it is possible to generate de novo genome sequences of comparable accuracy from Illumina sequencing to those obtained by Sanger sequencing.