THE APPLICATION OF SPORE SURFACE-FEATURES IN DEFINING TAXONOMIC VERSUS ECOLOGICAL GROUPINGS IN OOMYCETE FUNGI

The origin and structure of cyst surface components in oomycete fungi are described in relation to evaluating their use as taxonomic markers . The ontogeny, biochemistry, and morphological variations in the popu lations of peripheral vesicles that occur in the zoospores of members of the Peronosporomycetidae and Saprolegniomycetidae, which are discha rged upon encystment to give rise to spore surface components, are rev iewed. The use of the ornamentation of the cyst coat to define genera within the Saprolegniomycetidae and as an indicator of geographical an d host-specific clones within a species of Saprolegnia are reviewed. T he cyst coat of the fish pathogen Saprolegnia parasitica shows conside rable morphological diversity that appears to be independent of the ge ographic origin of isolates. There is an indication that a group of is olates with variable, relatively short, spines form a separate clone f rom those with larger hooped bundles. The monoclonal antibody probes t hat have been generated to spore surface components of Saprolegnia par asitica, Pythium aphanidermatum, and Phytophthora cinnamomi are summar ized and their use in defining taxonomic groups reviewed. The antibodi es show different levels of specificity ranging from isolate- to order -specific reactions. The degree of specificity can be influenced in so me cases by the immunoassay method used. These studies indicate that s urface structures and molecules provide extremely versatile and valuab le markers for use in oomycete taxonomy and phylogeny.