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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).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 borealis E Hansen, Sutton and Reeser was recovered 31 times from six of 49 sampled Alaskan streams, scattered from the Kenai Peninsula to Fairbanks. It was the third most frequently identified species in Alaska waters, after P. gonapodyides and P. riparia. It was not identified in extensive sampling in Oregon streams (Reeser et al. 2011). Phylogenetically it is in clade 6 with P. megasperma s.s., P. gonapodyides and a number of provisionally identified taxa (Brasier et al. 2003). It is readily distinguished by ITS DNA sequences from related Clade 6species.
1. Sporangia
Sporangia were persistent, ovoid or obpyriform and non-papillate, with a slight apical thickening. Sporangial length was 69 ± 10 μm (one standard deviation). Isolate mean sporangial length of six isolates was 64–75 μm. Sporangial breadth averaged 39 ± 7 μm. Length to breadth ratio of the six isolates averaged 1.8 with isolate mean ratios of 1.7–1.9. Sporangia formed in water. Sporangiophores were unbranched, exhibiting internal proliferation, both nested and extended. Subsporangial elongation was rarely observed.
2. Chlamydospores
Chlamydospores were not formed in agar.
3. Sex Organs
Phytophthora borealis was sexually self-sterile. It formed no oogonia in single-strain culture and formed oogonia only rarely when paired with mating type testers of heterothallic species. Although most P. borealis isolates were sexually sterile, one isolate formed oogonia inconsistently when paired with an A2 tester isolate of P. cryptogea. It did not induce oogonia in the tester isolate. In this and other morphological features it was similar to P. gonapodyides and some other sterile Clade 6 species, although colony growth pattern and optimum temperature were distinctive.
4. Growth Temperatures
Radial growth on CA at 25° C was about 2 mm/day, with a growth optimum (3.1 mm/day) 15–20° C. Slow growth was evident at 30° C, and no growth was observed at 35° C
5. Growth Characteristics in Culture
The colony pattern on CA was angular and petaloid, with hyphae appressed. On V8S agar growth was fluffy aerial with an underlying petaloid pattern.
6. Distinguishing Characteristics
Phytophthora borealis and P. riparia are similar in appearance to other Clade 6 species, although they are phylogenetically distinct. The relatively low optimum growth temperature of P. borealis is distinctive, and sporangia of this species are larger than others on average. 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. borialis is abundant in stream water in 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