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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).
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hytophthora siskiyouensis Reeser & E.M. Hansen 2008 (Oomycetes, Pythiales)
Distribution: North America (USA: OR).
Disease Note: Associated with cankers, pathogenicity little known.
Host: Lithocarpus densiflorus (Fagaceae), Umbellularia californica (Lauraceae).
Supporting Literature:
Reeser, P.W. , Hansen, E.M., and Sutton, W. 2007. Phytophthora siskiyouensis, a new species from soil, water, myrtlewood (Umbellularia californica) and tanoak (Lithocarpus densiflorus) in southwestern Oregon. Mycologia 99: 639-643.
Updated on Jun 17, 2008
Phytophthora siskiyouensis Reeser et E. M. Hansen was initially recovered in southwestern Oregon from rhododendron and tanoak leaf baits used for monitoring streams and soils for the presence of Phytophthora ramorum, from a blighted shoot of myrtlewood and from tanoak bark cankers. Phylogenetically it is a clade 2b species basal to P. capsici.
1. Sporangia
Sporangia were formed sparsely in V8S and abundantly on agar culture pieces placed in stream water. Sporangia varied widely in shape but were typically ovoid, reniform or some misshapen variant of these. Sporangia were scarcely semipapillate with prominent thickening (Fig 1). Semipapillae were applied apically, subapically or laterally, occasionally with two and more rarely with three semipapillae. Sporangiophores were simple, unbranched, short or long, attached basally, subbasally or laterally to the sporangium. A small hyphal swelling often was associated with the sporangiophore. Sporangia were typically terminal but were often subterminal and occasionally intercalary, and weakly deciduous with variable pedicel length (average 29 µm, individual pedicels 0–133 µm.) Sporangia for individual isolates averaged 46–70 µm long and 30–51 µm wide, (overall average 55 3 36 µm). Overall length to breadth ratio was 1.5, with a range of 1.1–2.0 for individual isolates.
2. Chlamydospores
Hyphal swellings or chlamydospores were not observed.
3. Sex Organs
Oogonia were formed abundantly on V8S in single culture and were usually globose to subglobose (or oblate), occasionally much elongated or with a funnel shape tapering toward the stalk (Fig 2). Oogonia were terminal on long or short stalks (often bent or kinked) and were frequently sessile and occasionally laterally intercalary. Average oogonial diameter for individual isolates was 24.8–30.3 µm (overall average 27.8 µm). Antheridia were predominately paragynous and capitate, with around 10% amphigynous. Antheridia were typically terminal, occasionally intercalary and usually diclinous, attached anywhere on the oogonium. Antheridia averaged 8.6–11.6 µm wide by 9.5–13.3 µm long. Oospores were globose to subglobose and usually aplerotic, sometimes markedly so in subglobose oogonia. Average oospore diameter for individual isolates was 22.5–25.8 µm (overall average 24.6 µm).
4. Growth Temperatures
Optimal temperature for growth of the nine isolates tested was 25 C. Radial growth rate averaged 7.5 mm/ d at 25° C (individual isolates were 6.2–8.5 mm/d at 25° C). Growth was slow at 5° C (average 0.84 mm/d) and almost nonexistent at 30° C (average 0.13 mm/ d). Cultures that did not grow at 5° C or 30° C recovered when removed to 20° C. No growth was observed at 35° C, and cultures did not recover when removed to 20° C
5. Growth Characteristics in Culture
Colonies on V8S were submerged with a faint radiate pattern and little or no aerial mycelium (Fig 3).
6. Distinguishing Characteristics
With its semipapillate sporangia and predominately paragynous antheridia, Phytophthora siskiyouensis would be placed in Waterhouse’s (1963) Group III, and its irregular sporangia are reminiscent of P. citricola. It is distinguished readily from this species however by having deciduous sporangia with variable length pedicels, variable orientation of semipapilla and sporangiophore attachment, intercalary and sessile attachment of some oogonia and mostly aplerotic oospores. P. siskiyouensis sporangia more resemble those depicted for P. quercina, except that they are slightly larger, semipapillate, weakly deciduous, and are formed singly on simple, unbranched sporangiophores. Sexual structures also resemble P. quercina, except that oogonia may be sessile or intercalary, and antheridia may be paragynous or amphigynous. The oogonial stalk an arrangement of paragynous antheridia are similar to those described for P. hedraiandra.
Phytophthora siskiyouensis was discovered first from streams and soil in areas dominated by native forest, and most isolates continue to come from these sources. Only later, and still infrequently, were isolates of the new species recovered from bole cankers on tanoak and only once from necrotic sprouts on myrtlewood. The species appears to be part of the native forest mycobiota of SW Oregon, associated with occasional symptoms on a variety of plants. More recently, Phytophthora siskiyouensis has been found killing Italian alder (Alnus cordata) in California (Rooney-Latham et al. 2009), and has been recovered from symptomatic roots and bark on native Alnus rubra in western Oregon. (Sims et al. 2012)
Reeser, P. W., Hansen, E. M., Sutton,W. 2007. Phytophthora siskiyouensis, a new species from soil, water, myrtlewood (Umbellularia californica) and tanoak (Lithocarpus densiflorus) in southwestern Oregon. Mycologia, 99: 639–643
Rooney-Latham, S., Blomquist, C. L., Pastalka, T., and Costello, L. 2009. Collar rot on
Italian alder trees in California caused by Phytophthora siskiyouensis. Online. Plant Health
Progress doi:10.1094/PHP-2009-0413-01-RS.
Sims, L., Hansen, E., and Navarro, S. 2012 Phytophthora species associated with Alnus rubra in western Oregon riparian ecosystems. (Abstr.) Sixth meeting of the International Union of Forest Research Organizations (IUFRO) Working Party S07.02.09: Phytophthoras in forests and natural ecosystems. Cordoba, Spain 9–14 September 2012.
Waterhouse, G. M. 1963. Key to the species of Phytophthora de Bary. Mycological Papers 92. Commonwealth Mycological Institute, Kew, UK.
This species page was adapted from Reeser et al. (2007) and Paul Reeser's additions to this text are gratefully acknowledged.
Isolate list
