The fungi which transmit plant viruses belong to class

The fungi which transmit plant viruses belong to class Plasmodiophoromycetes.
It is an odd group of endoparasites that live almost their entire life cycle inside a cell of another organism.
They lack cell walls in the assimilative state and reproduce using swimming spores (with two unequal whiplash flagella), the only part of their life cycle that does not occur inside a cell.