PROKARYOTIC HOSTS. “In prokaryotes, the great majority of viruses have dsDNA genomes, mostly within the range of 10–100 kb. The second most abundant class includes small ssDNA viruses. Retroelements comprise a small minority (no retroviruses are known), whereas RNA viruses are rare.”
http://onlinelibrary.wiley.com/doi/10.1111/nyas.12728/full