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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).
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Phytophthora obscura Grünwald & Werres has been recovered from several nursery plants in Oregon and soil underneath diseased Aesculus hippocastanum in Germany. Due to its morphological similarity to P. syringae it is possible this species can be misidentified. Phylogenetic analysis based on 7 nuclear loci and the mitochondrially encoded cox2 gene place this species in clade 8 with a close affiliation with P. syringae and P. austrocedrae.
1. Sporangia
Phytophthora obscura produces semipapillate, non-caducous sporangia on single, sympodial sporangiophores. Sporangia were generally ovoid but could also vary from globose to limoniform. Sporangia average 36.2 X 26.4 µm (range of 24 - 50 X 14 - 32 µm) with an average L:B ratio 1.4:1 and are abundantly formed on CPA after flooding with peat extract.
2. Chlamydospores
No chlamydospores produced.
3. Sex Organs
The species is homothallic and readily produced oogonia with paragynous antheridia in culture with one antheridium per oogonium. Oogonia were usually round, and sometimes a little irregular (mean diameter 33.4 µm with a range of 26 - 40 µm). Antheridia were mainly globose nearly globose (10.0 X 10.0 µm in average). Oospores were mainly plerotic, but mature oospores were sometimes slightly aplerotic with average diameter of 29.8 µm (range of 22 - 36 µm).
4. Growth Temperatures
Temperature optimum 25 C with daily a incremental radial growth average of 4.3 µm on CPA. Minimum temperature for growth is 2° C with a maximum of 20 - 25° C.
5. Growth Characteristics in Culture
Colonies grew smooth to slightly stellate on CPA, OMA and V8A, but cottony and slightly petaloid to stellate on PDA. Hyphal swellings were rarely observed. Mycelium showed a relatively low rate of branching.
6. Distinguishing Characteristics
Morphologically, P. obscura is more similar to P. syringae than to P. austrocedrae. Phytophthora obscura can easily be distinguished from P. austrocedrae mainly because of the slower growth, the bigger sporangia, and the different size and shape of the gametangia of the latter. Phytophthora obscura and P. syringae cannot be distinguished based on morphology alone. Ecologically, P. obscura might be comparable to P. syringae and considered to cause mostly foliar blight, twig blight and stem cankers on ornamentals or cankers on trees.
This species has been recovered from diseased leaf tissue of Kalmia latifolia, substrate underneath Pieris and from soil samples underneath Aesculus hippocastanum exhibiting disease symptoms. Pathogenicity tests have confirmed K. latifolia, A. hippocastanum, Rhododendron catawbiense and Pieris japonica as hosts. In Germany P. obscura is found in association with A. hippocastanum exhibiting bleeding cankers in urban plantations, but attempts to recover the pathogen from cankers has not been successful. Inoculation trials in the field have not been successful either, although this may be due to a need for longer incubations at lower temperatures for the pathogen to infect the tissue.
Grünwald, N. J., Werres, S., Goss, E. M., Taylor, C. R., Fieland, V. J. 2012. Phytophthora obscura sp. nov., a new species of the novel Phytophthora subclade 8d. Plant Pathology 61: 610-622.
This species page was adapted from Grünwald et al. (2012)
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