FUNGAL TRANSMISSION OF PLANT-VIRUSES

Thirty soilborne viruses or virus-like agents are transmitted by five species of fungal vectors. Ten polyhedral viruses, of which nine are i n the family Tombusviridae, are acquired in the in vitro manner and do not occur within the resting spores of their vectors, Olpidium brassi cae and O. bornovanus. Fungal vectors for other viruses in the family should be sought even though tombusviruses are reputed to be soil tran smitted without a vector. Eighteen rod-shaped viruses belonging to the furo- and bymovirus groups and to an unclassified group are acquired in the in vivo manner and survive within the resting spores of their v ector, O. brassicae, Polymyxa graminis, P. betae, and Spongospora subt erranea. The viral coat protein has an essential role in in vitro tran smission. With in vivo transmission a site in the coat protein-read th rough protein (CP-RT) of beet necrotic yellow vein furovirus determine s vector transmissibility as does a site in a similar 98-kDa polyprote in of barley mild mosaic bymovirus. The mechanisms by which virions mo ve (or are moved) into and out of the protoplasm of zoospores or of th alli needs study.