ABSTRACT
Intensive research over the last few decades has established that two main groups of root-inhabiting fungi, viz. certain members of Chytridiomycetes and Plasmodiophoromycetes are highly effi cient vectors of plant viruses (Barr 1988). They are obligate parasites which require living plants as their hosts to complete simple life cycle. Zoospores, a motile stage in their life cycles, function as virus vectors in the rhizosphere of host plants under appropriate environmental conditions. Two types of virus-fungal vector relationships are known; in the fi rst type, the virus is acquired in vivo in the virus-infected plant during replication of the fungus. Newly formed zoospores carry viral genome internally and transmit it to new hosts and/ or continue to maintain the virus throughout the dormant stage of resting spores, presumably as long as the resting spores remain viable. In the second type, virus acquisition occurs by virus adsorption to the surface of active zoospores prior to cyst formation. Since the virus does not remain internally, the nature of virus-vector association is short-term and thus the virus does not persist in the resting spores that emerge from virus-infected plants. In this chapter the emphasis will be focused on the methods established for the maintenance of the cultures of known vector-fungi as well as on a brief description of environmental factors that affect the maintenance of the fungal cultures. For detailed discussions of different virus-vector fungus systems, further reading of review paper is recommended (Campbell 1979, 1988, Teakle 1988, Hiruki and Teakle 1987, Brunt 1989).
