Phytophthora has been rebuilt to fix security-related problems and to restore GIS tools. These tools allow users to visualize the geospatial, temporal, and environmental contexts of Phytophthora discoveries. The next phase is to update species information and add data derived from large-scale surveys. If you have suggestions and requests to make the database better, please contact Seogchan Kang (sxk55@psu.edu).
Genus wide phylogeny for Phytophthora using four mitochondrial loci (cox2, nad9, rps10 and secY; 2,373 nucleotides). Maximum likelihood branch lengths shown. Numbers on nodes represent bootstrap support values for maximum likelihood (top), maximum parsimony (middle) and Bayesian posterior probabilities as percentages (bottom). Nodes receiving significant support (>95%) in all analysis are marked with an asterisk (*). Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).
[ Click the tree to enlarge it. ]
Phytophthora riparia Reeser, Sutton and E Hansen was identified in recent Phytophthora surveys of forest streams in Oregon, California and Alaska and phylogenetically is placed in clade 6 with P. lacustris as the closest relative. Phytophthora riparia was recovered 64 times from 10 of 49 sampled Alaska streams, from the Kenai Peninsula to Fairbanks (Hansen et al. 2012). It was the second most frequently identified species in Alaska waters, after P. gonapodyides. It also was identified in multiple water samples and a single riparian soil sample from western Oregon (Reeser et al. 2011) and California streams. It did not appear in the extensive sampling from SW Oregon. Phytophthora riparia was referred to as P. New species 2 in Reeser et al (2011).
Speciation processes remain puzzling in some clonal lineages of P. riparia as do the selective processes that maintain species identities. Our limited understanding is highlighted by the single “hybrid” isolate that was observed (Hansen et al. 2012). Isolate EBE1.8.27 is plausibly the product of a somatic fusion between individuals of P. riparia and P. taxon Salixsoil (this provisional species has been renamed P. lacustris, Nechwatal et al. 2012). It clusters with P. riparia in the ITS phylogeny, but β-tubulin sequence mixes nucleotides from both parents, and cox I sequence is identical to P. lacustris. This isolate is perhaps the product of the sorting out of organelles after the chance meeting and fusion of two zoospores.
1. Sporangia
Sporangia were ovoid or obpyriform, non-papillate, with a slight apical thickening, and not caducous. Mean sporangial length was 55 ± 10 μm (one standard deviation), with isolate means of 47–62 μm. Sporangial breadth averaged 31 ± 4 μm. Length to breadth ratio of the six isolates averaged 1.8 with isolate mean ratios of 1.6–2.1. Sporangia formed in water. Sporangiophores were unbranched, exhibiting internal proliferation, both nested and extended. Subsporangial elongation was observed rarely.
2. Chlamydospores
Chlamydospores were not formed in agar.
3. Sex Organs
Phytophthora riparia was sexually sterile, with no oogonia formed in single-strain culture or when paired with mating type testers of heterothallic species.
4. Growth Temperatures
Radial growth on CA at 25° C was about 2.4 mm/day, with a growth optimum (2.6 mm/day) near 30° C. Slow growth was measured at 35° C, but no growth occurred at 40° C
5. Growth Characteristics in Culture
The colony pattern on V8S and on CA was angular and petaloid, with hyphae appressed
6. Distinguishing Characteristics
Many species in Phytophthora Clade 6, including Phytophthora borealis and P. riparia, present very similar morphological and behavioral profiles. They are “good” phylogenetic species and often can be distinguished by subtle differences in growth pattern, but they are difficult to identify reliably without DNA sequencing tools. They undoubtedly have been misidentified, as P. drechsleri or P. cryptogea (Hansen et al. 1988), or lumped with P. gonapodyides (Brasier et al 1993).
P. riparia is abundant in stream water in Oregon, California and Alaska but is not overtly pathogenic; at least it has not been associated with disease in adjacent riparian ecosystems.
Brasier, C., Hamm, P. B., Hansen, E. M. 1993. Cultural characters, protein patterns and unusual mating behavior of Phytophthora gonapodyides isolates from Britain and North America. Mycol. Res. 97:1287–1298.
Hansen, E. M., Reeser, P. W., Sutton, W. 2012. Phytophthora borealis and Phytophthora riparia, new species in Phytophthora ITS Clade 6. Mycologia: In Press. doi:10.3852/11-349
Hansen, E., Hamm, P.B., Hennon. P., Shaw, III C. G. 1988. Phytophthora drechsleri from remote areas of southeast Alaska. Trans. Br. Mycol. Soc. 91:379–384.
Nechwatal, J., Bakonyi, J., Cacciola, S.O., Cooke, D. E. L., Jung, T., Nagy, Z. A., Vannini, A., Vettraino, A. M., Brasier, C. M. 2012. The morphology, behaviour and molecular phylogeny of Phytophthora taxon Salixsoil and its redesignation as Phytophthora lacustris sp. nov. Plant Pathology Doi:10.1111/j.1365-3059.2012.02638.x
Reeser, P. W., Hansen, E, M., Sutton, W., Remigi, P., Adams, G. C. 2011. Phytophthora species in forest streams in Oregon and Alaska. Mycologia 103:22–35.
This species page was adapted from Hansen et al. (2012)
Isolate list