Morphology and Taxonomy of the Oomycetes, With Special Reference to Saprolegniaceae, Leptomitaceae and Pythiaceae

Abstract

SUMMARYThe morphology of sexual reproduction is reviewed and the importance of developmental stages is considered. Particular attention is drawn to the taxonomie significance of the size, wall structure and protoplasmic organization of the oospore.

Saprolegniaceae identified on amphibian eggs throughout the Pacific Northwest, USA, by internal transcribed spacer sequences and phylogenetic analysis

“…colorata. These Achlya subgroups are consistent with divisions based on oospore morphology outlined by Dick (1969). None of our eight isolates from field samples directly matched sequences of our reference Achlya species, so we are unsure of their species-level taxonomy.…”

Morphological and molecular phylogenetic analysis of two Saprolegnia sp. (Oomycetes) isolated from silver crucian carp and zebra fish

“…All these results show that isolates JY and BMY may be conspecific. According to the classical taxonomic criteria (Dick 1969;Seymour 1970;Johnson et al 2002), the two isolates were morphologically closest to S. australis and S. ferax, in having smooth or unsmooth oogonia, variably present antheridia and up to 30 or more, centric or subcentric oospores. It should be noted that relatively few mature oospores are produced and in isolate BMY many oogonia contain 50 or so spores which are abnormally small for oospores.…”

“…However, identification of the causative agent is often difficult, especially for isolates taken from fish lesions and infested eggs. Traditional classification is mainly based on the precise descriptions of sexual reproductive organs including oogonia, antheridia, antheridial branch origin, oogonium ornamentation, oospore and lipid droplet position in the oospore (Dick 1969;Seymour 1970;Willoughby 1978;Neish & Hughes 1980;Leclerc et al 2000). Unfortunately, many isolates obtained from animals often fail to produce sexual structures in vitro (Hatai et al 1990;Stueland et al 2005;Dié guez-Uribeondo et al 2007) or form these structures only after a long developmental time (Leclerc et al 2000) or immature oogonia are aborted (Seymour 1970;Johnson et al 2002).…”

Sensitivities of various Oomycetes to hymexazol and metalaxyl

“…Adsorption by mucilages (carbohydrate or protein) secreted through the cell wall and deposited on the surface of the cell wall. Differential secretion of mucilages has been described : for example the oogonial mucilage of Aplanopsis (Dick, 1969).…”