Halophytophthora Species Research Articles

Pathogenicity of Phytophthora and Halophytophthora species on black alder and the host histological response

Riparian alder forests are threatened by Phytophthora across Europe. Comparative studies of the pathogenicity of Phytophthora species are crucial for developing effective management strategies. Although only a limited number of species, particularly P. × alni, lead to tree decline in natural environments, many species demonstrate pathogenicity in inoculation trials. Phytophthora species vary in their ability to infect different tissues, such as phloem and xylem, and trigger defence responses in the host through the formation of tyloses and callose. By comparing the histological responses of alder to various Phytophthora species, we can gain insights into the success of P. × alni and the potential damage that could be caused by other species. To investigate the defence strategies of black alder (Alnus glutinosa) against attack by Phytophthora and Halophytophthora species present in Catalonia (NE Spain), we conducted inoculation trials on saplings using nine potentially pathogenic species and compared the histological responses. Phytophthora × alni and P. plurivora were the most aggressive species followed by other exotic species such as P. × cambivora and P. cactorum. Phytophthora × alni and P. plurivora were equally damaging despite the higher prevalence of P. × alni in declining alders in natural settings. Although P. × alni mainly invaded the phloem, P. plurivora also invaded the xylem and triggered the production of tyloses. Histological analyses revealed a diverse range of plant responses to infection by Phytophthora species, providing a better understanding of their adaptability in natural environments compared with solely observing lesions. The low level of callose production in saplings inoculated with P. × alni compared with callose production in saplings inoculated with less pathogenic species suggests that P. × alni can evade recognition by the host and, hence, could partially explain its success.

Unravelling the Lipids Content and the Fatty Acid Profiles of Eight Recently Described Halophytophthora Species and H. avicennae from the South Coast of Portugal.

In this study, mycelia of eight recently described species of Halophytophthora and H. avicennae collected in Southern Portugal were analysed for lipids and fatty acids (FA) content to evaluate their possible use as alternative sources of FAs and understand how each species FAs profile relates to their phylogenetic position. All species had a low lipid percentage (0.06% in H. avicennae to 0.28% in H. frigida). Subclade 6b species contained more lipids. All species produced monounsaturated (MUFA), polyunsaturated (PUFA) and saturated (SFA) FAs, the latter being most abundant in all species. H. avicennae had the highest FA variety and was the only producer of γ-linolenic acid, while H. brevisporangia produced the lowest number of FAs. The best producer of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) was H. thermoambigua with 3.89% and 9.09% of total FAs, respectively. In all species, palmitic acid (SFA) was most abundant and among the MUFAs produced oleic acid had the highest relative percentage. Principal component analysis (PCA) showed partial segregation of species by phylogenetic clade and subclade based on their FA profile. H. avicennae (Clade 4) differed from all other Clade 6 species due to the production of γ-linolenic and lauric acids. Our results disclosed interesting FA profiles in the tested species, adequate for energy (biodiesel), pharmaceutical and food industries (bioactive FAs). Despite the low amounts of lipids produced, this can be boosted by manipulating culture growth conditions. The observed interspecific variations in FA production provide preliminary insights into an evolutionary background of its production.

Eight new Halophytophthora species from marine and brackish-water ecosystems in Portugal and an updated phylogeny for the genus.

During an oomycete survey in December 2015, 10 previously unknown Halophytophthora taxa were isolated from marine and brackish water of tidal ponds and channels in saltmarshes, lagoon ecosystems and river estuaries at seven sites along the Algarve coast in the South of Portugal. Phylogenetic analyses of LSU and ITS datasets, comprising all described Halophytophthora species, the 10 new Halophytophthora taxa and all relevant and distinctive sequences available from GenBank, provided an updated phylogeny of the genus Halophytophthora s.str. showing for the first time a structure of 10 clades designated as Clades 1-10. Nine of the 10 new Halophytophthora taxa resided in Clade 6 together with H. polymorphica and H. vesicula. Based on differences in morphology and temperature-growth relations and a multigene (LSU, ITS, Btub, hsp90, rpl10, tigA, cox1, nadh1, rps10) phylo-geny, eight new Halophytophthora taxa from Portugal are described here as H. brevisporangia, H.cele-ris, H.frigida, H. lateralis, H. lusitanica, H. macrosporangia, H. sinuata and H. thermoambigua. Three species, H.frigida, H.macrosporangia and H. sinuata, have a homothallic breeding system while the remaining five species are sterile. Pathogenicity and litter decomposition tests are underway to clarify their pathological and ecological role in the marine and brackish-water ecosystems. More oomycete surveys in yet undersurveyed regions of the world and population genetic or phylogenomic analyses of global populations are needed to clarify the origin of the new Halophytophthora species. Citation: Maia C, Horta Jung M, Carella G, et al. 2022. Eight new Halophytophthora species from marine and brackish-water ecosystems in Portugal and an updated phylogeny for the genus. Persoonia 48: 54 - 90. https://doi.org/10.3767/persoonia.2022.48.02..

Eight new Halophytophthora species from marine and brackish-water ecosystems in Portugal and an updated phylogeny for the genus

During an oomycete survey in December 2015, 10 previously unknown Halophytophthora taxa were isolated from marine and brackish water of tidal ponds and channels in saltmarshes, lagoon ecosystems and river estuaries at seven sites along the Algarve coast in the South of Portugal. Phylogenetic analyses of LSU and ITS datasets, comprising all described Halophytophthora species, the 10 new Halophytophthora taxa and all relevant and distinctive sequences available from GenBank, provided an updated phylogeny of the genus Halophytophthora s. str. showing for the first time a structure of 10 clades designated as Clades 1–10. Nine of the 10 new Halophytophthora taxa resided in Clade 6 together with H. polymorphica and H. vesicula. Based on differences in morphology and temperature-growth relations and a multigene (LSU, ITS, Btub, hsp90, rpl10, tigA, cox1, nadh1, rps10) phylogeny, eight new Halophytophthora taxa from Portugal are described here as H. brevisporangia, H. celeris, H. frigida, H. lateralis, H. lusitanica, H. macrosporangia, H. sinuata and H. thermoambigua. Three species, H. frigida, H. macrosporangia and H. sinuata, have a homothallic breeding system while the remaining five species are sterile. Pathogenicity and litter decomposition tests are underway to clarify their pathological and ecological role in the marine and brackish-water ecosystems. More oomycete surveys in yet undersurveyed regions of the world and population genetic or phylogenomic analyses of global populations are needed to clarify the origin of the new Halophytophthora species.

Halophytophthora fluviatilis Pathogenicity and Distribution along a Mediterranean-Subalpine Gradient.

Halophytophthora species have been traditionally regarded as brackish water oomycetes; however, recent reports in inland freshwater call for a better understanding of their ecology and possible pathogenicity. We studied the distribution of Halophytophthora fluviatilis in 117 forest streams by metabarcoding river filtrates taken in spring and autumn and by direct isolation from floating leaves. Pathogenicity on six Fagaceae species and Alnus glutinosa was assessed by stem inoculations. The distribution of H. fluviatilis was correlated with high mean annual temperatures (>93.5% of reports in Ta > 12.2 °C) and low precipitation records. H. fluviatilis was therefore widely distributed in forest streams in a warm–dry climate, but it was mostly absent in subalpine streams. H. fluviatilis was primarily detected in autumn with few findings in spring (28.4% vs. 2.7% of streams). H. fluviatilis was able to cause small lesions on some tree species such as Quercus pubescens, Q. suber and A. glutinosa. Our findings suggest that H. fluviatilis may be adapted to warm and dry conditions, and that it does not pose a significant threat to the most common Mediterranean broadleaved trees.

Marine Oomycetes of the Genus Halophytophthora Harbor Viruses Related to Bunyaviruses.

We investigated the incidence of RNA viruses in a collection of Halophytophthora spp. from estuarine ecosystems in southern Portugal. The first approach to detect the presence of viruses was based on the occurrence of dsRNA, typically considered as a viral molecule in plants and fungi. Two dsRNA-banding patterns (∼7 and 9 kb) were observed in seven of 73 Halophytophthora isolates tested (9.6%). Consequently, two dsRNA-hosting isolates were chosen to perform stranded RNA sequencing for de novo virus sequence assembly. A total of eight putative novel virus species with genomic affinities to members of the order Bunyavirales were detected and their full-length RdRp gene characterized by RACE. Based on the direct partial amplification of their RdRp gene by RT-PCR multiple viral infections occur in both isolates selected. Likewise, the screening of those viruses in the whole collection of Halophytophthora isolates showed that their occurrence is limited to one single Halophytophthora species. To our knowledge, this is the first report demonstrating the presence of negative (−) ssRNA viruses in marine oomycetes.

Salinity, pH and temperature growth ranges of Halophytophthora isolates suggest their physiological adaptations to mangrove environments

ABSTRACT Species of Halophytophthora are early colonisers of fallen mangrove leaves in the tropics but recently found commonly in temperate areas. In mangrove habitats, temperature and salinity change rapidly daily (high/low tide) and seasonally (summer/winter, rainy/dry seasons). Mangrove organisms have to develop adaptive strategies to thrive in such a physiologically challenging environment. In this study, growth of three isolates of Halophytophthora avicenniae and two isolates of H. batemanensis was tested under combined effects of 3 temperatures (15°C, 25°C, 37°C), 3 pHs (6, 7, 8) and 4 salinities (4 ‰, 8 ‰, 16 ‰, 32 ‰). No/little growth was observed at 37°C and growth saturation occurred earlier at 25°C than at 15°C. The log phase of growth was steeper at pH 6 than pH 7 and 8. Temperature and pH were found to exert a greater effect on growth than salinity. Generally, a reduction of growth rate was observed at pH 8 and 15°C. Increase in salinity caused a slight decrease in growth, most noticeable at 32 ‰. The wide growth ranges of temperature, salinity and pH of Halophytophthora isolates suggest that they are well adapted to the physical and chemical conditions of mangrove habitats.

Two new species of Halophytophthora from Brazil

During a survey of oomycetes in a mangrove area of Sao Paulo state, Brazil, a high number of isolates of Halophytophthora and related genera were recovered from leaves and water samples. In this study, we analysed the morphology and phylogenetic relationships of the isolates of Halophytophthora along with four ex-types provided by CBS-KNAW Culture Collection. Maximum likelihood and Bayesian analyses of the internal transcribed spacer (ITS) and large subunit (LSU) rDNA regions confirmed previous evidence of the polyphyly of the genus and revealed the presence of two yet undescribed species. The two new species, Halophytophthora souzae and H. insularis, belong to the Halophytophthora sensu stricto clade and are described herein based on their morphology and/or phylogenetic position.

Revisiting Salisapiliaceae.

Of the diverse lineages of the Phylum Oomycota, saprotrophic oomycetes from the salt marsh and mangrove habitats are still understudied, despite their ecological importance. Salisapiliaceae, a monophyletic and monogeneric taxon of the marine and estuarine oomycetes, was introduced to accommodate species with a protruding hyaline apical plug, small hyphal diameter and lack of vesicle formation during zoospore release. At the time of description of Salisapilia, only few species of Halophytophthora, an ecologically similar, phylogenetically heterogeneous genus from which Salisapilia was segregated, were included. In this study, a revision of the genus Salisapilia is presented, and five new combinations (S. bahamensis, S. elongata, S. epistomia, S. masteri, and S. mycoparasitica) and one new species (S. coffeyi) are proposed. Further, the species description of S. nakagirii is emended for some exceptional morphological and developmental characteristics. A key to the genus Salisapilia is provided and its generic circumscription and character evolution in cultivable Peronosporales are discussed.

Multiple Halophytophthora spp. and Phytophthora spp. including P. gemini, P. inundata and P. chesapeakensis sp. nov. isolated from the seagrass Zostera marina in the Northern hemisphere

A plethora of oomycetes was isolated mostly from Zostera marina but also from other halophilic plants originating from several locations including the Wadden Sea, Limfjord (Denmark), the Dutch Delta area (the Netherlands), Thau lagoon (France), Lindholmen (Sweden) and Chesapeake Bay (Virginia, U.S.). Based on ITS sequences, seven different groups could be distinguished. The largest group was assigned to Phytophthora gemini (Germany, Sweden, the Netherlands, U.S.). The CoxI sequences of all P. gemini strains were identical indicating that P. gemini is probably an invasive species in the Wadden Sea. A second group was identified as P. inundata (the Netherlands, Denmark), that was also isolated from the halophilic plants Aster tripolium and Salicornia europaea. Four strains, originating from Chesapeake Bay clustered in a monophyletic clade with high bootstrap support at the ITS as well as the CoxI loci. They are phylogenetically closely related to P. gemini and are considered to represent a new species described here as Phytophthora chesapeakensis sp. nov. In addition, Salisapilea sapeloensis was isolated from Zostera noltii. Eleven other strains belonging to three unidentified taxa, originating from the Wadden Sea, the Dutch Delta area and Thau lagoon, clustered each in a monophyletic clade with high bootstrap support at the ITS locus, including Halophytophthora vesicula, the type species of the genus Halophytophthora. Hence, these strains were considered to belong to the Halophytophthora sensu stricto group and probably represent three new Halophytophthora species, informally designated here as Halophytophthora sp-1, Halophytophthora sp-3 and Halophytophthora sp-4 sensu Nigrelli and Thines. Halophytophthora sp-2 was not detected in this study. In addition, P. gemini and Halophytophthora sp-3 were obtained by baiting from locations in the Wadden Sea and Halophytophthora sp-1 was obtained by baiting from the Delta area.

The genus Halophytophthora (Peronosporales, Straminipila) in Brazil: first descriptions of species

Halophytophthora spp. are considered as one of the most important decomposers of fallen mangrove leaves worldwide. The knowledge of the diversity of straminipiles in Brazilian mangrove swamps is very limited, and there are no previous descriptions of Halophytophthora species for Brazil. Our aim was to identify and describe the specimens isolated from fallen mangrove leaves and water samples collected in a mangrove swamp at “Parque Estadual da Ilha do Cardoso” on the basis of morphological and molecular data (partial large subunit and complete internal transcribed spacer sequences from the rDNA). We recovered 33 isolates belonging to three species of the “Halophytophthora s.s.” clade: H. vesicula (75 % frequency), H. polymorphica (16.7 %) and H. avicenniae (8.3 %). All of these species are described for the first time for Brazil, while Halophytophthora polymorphica and H. avicenniae are also new records for South America.

Production of arachidonic and eicosapentaenoic acids by the marine oomycete Halophytophthora.

Polyunsaturated fatty acids (PUFAs) are fatty acids with more than one double bond in the chemical structure. Arachidonic acid (ARA, 20:4 (n-6)) and eicosapentaenoic acid (EPA, 22:5 (n-3)) are common PUFAs with beneficial health effects. Marine fish and meat are the main sources of omega-3 and omega-6 fatty acids in human's diet, respectively. In particular, there is a general decline in fish catch, implicating the need for an alternative source of omega-3 fatty acids. Previous studies have examined the production of polyunsaturated fatty acids including ARA and EPA by various microorganisms, including microalgae, fungi, and thraustochytrids. In this study, the production of ARA and EPA by 10 isolates of four estuarine Halophytophthora species (Halophytophthora avicenniae, Halophytophthora polymorphica, Halophytophthora vesicula, and Halophytophthora spinosa var. spinosa) cultured from fallen mangrove leaves in Taiwan was examined. The yield of ARA ranged from 0.004 to 0.052 g/L with the highest yield of ARA obtained from H. spinosa var. spinosa IMB162, but no or a very low level of EPA was produced by IMB162. For EPA production by Halophytophthora spp., the yield ranged from 0 to 0.047 g/L. Percentage of ARA in total fatty acid ranged between 7.16 and 25.02%. One-way ANOVA analysis using Tukey Test (p ≥ 0.05) suggested that there is significant difference in the percentage of EPA in total fatty acid produced by the isolates, which ranged from 0.01 to 18.42%. BODIPY 505/515 fluorescent staining suggests that lipid bodies were evenly distributed in the mycelia of Halophytophthora species.

Tropical oomycetes in the German Bight – Climate warming or overlooked diversity?

Oomycetes have colonised both terrestrial and marine habitats, and leaf litter decomposing oomycetes have been found in coastal and estuarine environments, yet their ecological relevance remains unclear. In tropical and subtropical ecosystems, Halophytophthora species were reported from mangroves and salt marshes, and recently, the genus Salisapilia was described based on oomycetes recovered from leaf litter in subtropical Georgia, USA. In cool temperate regions, only Pythium and Phytophthora species have so far been reported from coastal environments. Here we report the presence of two species of Halophytophthora in the German Bight, north of Hamburg. The presence of a group of oomycetes, previously reported only from the subtropics and tropics, in the cool temperate German Bight raises the question of whether these were previously overlooked, introduced with ballast water or have migrated there as a result of climate change. Temperature preference of the strains hints at the first hypothesis. ► The tropical oomycete genus Halophytophthora is also present in the German Bight. ► Same species present in subtropical Georgia, USA and in the temperate German Bight. ► Local adaptation in strains from the North Sea, tolerating high temperatures less.

Fishing for Phytophthora from Western Australia’s waterways: a distribution and diversity survey

During one spring season, 12 Phytophthora species, two Phytophthora hybrids, three Halophytophthora species and three Phytopythium species, were isolated from 48 waterways across Western Australia. The waterways were sampled using nylon mesh bags containing leaf baits of up to six different plant species and were isolated by plating necrotic lesions on these onto Phytophthora-selective agar media. Phytophthora species were isolated from all except one waterway. Of the Phytophthora species isolated, eight are known while the remaining four are undescribed taxa. Six of the Phytophthora species and the two hybrids are from clade 6. The two hybrids and P. inundata were the predominant species recovered. Recoveries from different plant leaf baits varied with the best two baits being Pittosporum undulatum and Banksia attentuata; and from these two combined all Phytophthora species were isolated. There was a marked difference in the Phytophthora diversity in the waterways from different regions. This is the first comprehensive study from Australia to examine the Phytophthora communities in waterways, and advances our understanding of the role of these oomycetes in natural and anthropized ecosystems.

Phytophthora species in forest streams in Oregon and Alaska

Eighteen Phytophthora species and one species of Halophytophthora were identified in 113 forest streams in Alaska, western Oregon and southwestern Oregon that were sampled by baiting or filtration of stream water with isolation on selective media. Species were identified by morphology and DNA characterization with single strand conformational polymorphism, COX spacer sequence and ITS sequence. ITS Clade 6 species were most abundant overall, but only four species, P. gonapodyides (37% of all isolates), P. taxon Salixsoil, P. taxon Oaksoil and P. pseudosyringae, were found in all three regions. The species assemblages were similar in the two Oregon regions, but P. taxon Pgchlamydo was absent in Alaska and one new species present in Alaska was absent in Oregon streams. The number of Phytophthora propagules in Oregon streams varied by season and in SW Oregon, where sampling continued year round, P. taxon Salixsoil, P. nemorosa and P. siskiyouensis were recovered only in some seasons.

Effect of Copper(II), Lead(II), and Zinc(II) on Growth and Sporulation of Halophytophthora from Taiwan Mangroves

This study evaluated the effect of lead (Pb(II)), zinc (Zn(II)) and copper (Cu(II)) on growth and sporulation of four Halophytophthora species (Halophytophthora vesicula, Halophytophthora elongata, Halophytophthora spinosa var. lobata, and an oogonia-producing Halophytophthora sp.) isolated from different mangrove sites in Taiwan. Results show that all isolates grew well or even better at 1 ppm concentration of the heavy metals tested. Growth of all test isolates was totally inhibited at 500 ppm, except for H. spinosa var. lobata exposed to Zn(II). For sporulation, all isolates produced moderate to abundant zoosporangia or oogonia at 1 ppm Pb(II) and Zn(II). Production of zoosporangia by H. vesicula, H. elongata and H. spinosa var. lobata was significantly affected or totally inhibited at 1 ppm Pb(II) and Zn(II) and all concentrations of Cu(II). Abnormal oogonia were produced by Halophytophthora sp. at 10 ppm Cu(II) and 100 ppm of the three heavy metals. In general, Cu(II) and Zn(II) were found to be the most toxic, and the least toxic was Pb(II). H. spinosa var. lobata was the most tolerant to all the heavy metals, while H. vesicula and H. elongata were the most sensitive. Results of this study shows that increased concentrations of Pb(II), Cu(II), and Zn(II) in the mangrove environment can significantly affect growth and impair normal reproduction of Halophytophthora species.

Tropical mangrove leaf litter fungi in Singapore with an emphasis on Halophytophthora

A study on the mangrove leaf litter fungi of two tropical mangroves in Singapore was carried out. Five Halophytophthora species and four isolates which did not fit the descriptions of known species were isolated from leaves of Avicennia alba, A. rumphiana, Rhizophora apiculata and R. mucronata. Halophytophthora exoprolifera, H. kandeliae, H. operculata, H. spinosa var. lobata and H. vesicula are new records for Singapore; the first three also being new records for tropical mangroves. The isolate of H. exoprolifera sporulated at 28 °C and may be a tropical strain. H. operculata is reported for the first time outside of Australia. The results of this study contribute to the little known distribution of the Halophytophthora in the Indian Pacific region. Thirteen deuteromycetes were also isolated from the mangrove leaf litter and represented both phylloplane fungi as well as possible marine fungi.

Competition among mangrove oomycotes, and between oomycotes and other microbes

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 12:21-28 (1997) - doi:10.3354/ame012021 Competition among mangrove oomycotes, and between oomycotes and other microbes Newell SY, Fell JW Competition experiments were performed using precolonized leaves or leaf disks of red mangrove Rhizophora mangle with: (1) disks containing pure cultures of single species of marine true fungi or species of Halophytophthora (the principal genus of marine oomycotes); and (2) leaves bearing bacterial films. Preoccupied leaves were exposed to natural microflorae in mangrove creeks at 2 Cays in the Bahama Islands, or placed in laboratory seawater enclosures wherein pairs of halophytophthoras were given equivalent opportunity to occupy fresh leaf material. The ubiquitous coastal-marine oomycote H. vesicula was found to be an able competitor versus true fungi and versus other halophytophthoras. Against other halophytophthoras, this was true for both primary and secondary resource capture. The one exception among the fungi was a species (Dendryphiella salina) common in decaying drift material in high-intertidal zones. H. spinosa was a weak competitor with true fungi and with H. vesicula, though it was not displaced by H. vesicula, and H. spinosa could depress the frequency of H. vesicula occupation when H. spinosa was well established. H. bahamensis did not routinely form sporangia, preventing identification and firm conclusions regarding competitiveness, other than that it could not block H. vesicula, but could block H. spinosa from entering its occupied arenas. When bacterial films were present on leaves prior to access by halophytophthoras, the occupation frequency of halophytophthoras was sharply depressed (by about 70 to 90% with 48 h bacterial films), including for H. vesicula, implying that in some types or parts of mangrove systems, submerged-leaf decomposition may sustain low levels of participation by halophytophthoras. Oomycotes · Halophytophthora · Fungi · Bacteria · Competition · Mangrove · Rhizophora Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 12, No. 1. Publication date: January 30, 1997 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1997 Inter-Research.

Cues for Zoospore Release by Marine Oomycotes in Naturally Decaying Submerged Leaves

Two common potential environmental impacts upon leaf-decomposers in the marine intertidal zone (mild drying, dilution of salinity/lowering of temperature due to rainfall) were simulated and tested as enhancers of zoospore release by species of Halophytophthora. Senescent leaves of mangroves and oak were used as bait in flow-through chambers to quantitate zoospore passage from disks of naturally decaying leaves. Older-decaying leaves of red and black mangrove had low rates of zoospore release by H. vesicula, the predominant oomycote encountered (< 15% of bait samples occupied in 24 h), and environmental cues had no detectable effect. Younger-decaying leaves of red mangrove had considerably higher rates of release, and rates were stimulated 2-fold by dilution (to 50% of bait samples positive). Rates for oak leaves were doubled by both dilution and drying (to 86–92% positive). We speculate that: i) halophytophthoras complete their occupation of submerged leaves (from attachment of zoospore cysts to release of zoospores from sporangia) early in the decomposition of leaves, before substantial entry into the leaves of labyrinthulids (predators); ii) environmental cuing results in high concentrations of halo- phytophthoran zoospores in shallow sheets or pools of low-tidal waters, enhancing probability of rapid contact with new-fallen leaves.

Do halophytophthoras (marine Pythiaceae) rapidly occupy fallen leaves by intraleaf mycelial growth

Low estimates (2 ∙ L−1) of concentrations of zoospores of Halophytophthora in mangrove water columns seem counterintuitive when compared with rapid rates of occupation of fallen mangrove leaves (100% frequency of occurrence after 24–30 h). One potential explanation is that lateral extension of mycelium within leaves is rapid after establishment of single zoospores. We tested this hypothesis by exposing single leaves in both mangrove and temperate salt-marsh ecosystems, with the upper half of leaves freely exposed to zoospore contact, and the lower half protected behind 8-μm screening. We found no evidence that mycelial growth within leaves was rapid enough to account for the rapid occupation of freely exposed leaves. Of the four Halophytophthora species commonly found (H. kandeliae, H. masteri, H. spinosa var. spinosa, and H. vesicula), only H. masteri appeared to have substantial capability for its zoospores to pass the screening. In temperate salt-marsh waters, H. kandeliae took the place of H. spinosa as co-occupier of leaves with H. vesicula. Two rare species (H. bahamensis and H. epistomium) originally described from subtropical mangrove environs were found in temperate salt-marsh samples. Key words: oomycotes, oomycetes, Halophytophthora, mangrove, salt marsh.