PARALLEL TESTING OF MEDIA FOR MEASURING FREQUENCIES OF OCCURRENCE FOR HALOPHYTOPHTHORA SPP (OOMYCOTA) FROM DECOMPOSING MANGROVE LEAVES

Samples of submerged, decaying leaves of red, black, and white mangroves (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa) were incubated on plates of eight different combinations of fungal inhibitors, bacterial inhibitors, and sporangium inducers added to a standard agar medium for isolating oomycotes (Protoctista: Oomycota; alias Oomycetes). The broad spectrum of agar preparations revealed no new oomycotic species for red or white mangroves; Halophytophthora vesicula (the delicate form) and Halophytophthora spinosa were overwhelmingly the most frequent species (to 88-90%,, depending on medium, mangrove, and site). Other described species of Halophythophthora were rare (e.g., Halophytophthora bahamensis occurred twice, versus a total of 263 occurrences for H. spinosa). For black mangrove, however, the predominant oomycote (frequency ranging up to 90%, depending on medium and site) was an undescribed species of Halophytophthora with a mechanism of zoospore release involving the expansion of a clear plug into a tubular vesicle. Halophytophthora vesicula and H. spinosa occurred at almost four times lower frequencies on black mangrove than the undescribed Halophytophthora species. Media without inhibitors allowed interference from bacteria and labyrinthulas, with consequent reduction of oomycote frequencies by as much as a factor of four. Chloramphenicol application as the sole inhibitor at 150 mg.L(-1) resulted in significant interference from eumycotic fungi (oomycote frequency reductions to x10). The best medium for exposing maximum frequencies of all three of the principal halophytophthoras was one with amphotericin B(2 mg.L(-1)) as the polyene-macrolide fungal inhibitor.