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).
* This species has not yet been formally described and should be treated as such.
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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).
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Isolates classified with the provisional species name P. sp. ohioensis were recovered from soils collected around a declining mature white oak tree (Quercus alba) in Ohio. It was associated with oak roots and not aboveground portions of the tree. In phylogenetic analysis using 6 nuclear loci it is in clade 4 closely related to P. quercina (Y. Balci, unpublished). The following description was based on data collected by Dr. Y. Balci for isolates collected form a single site with a formal description awaiting availability of isolates collected from additional locations (currently in progress).
1. Sporangia
Sporangia produced abundantly in soil extract water after 1 to 3 days but seldom on solid agar (V8A). Sporangiophores are sympodial without internal proliferation. Sporangia always terminal, papillate and non-caducous with terminal papilla (FIGS. 1 A-J). Sporangia mainly ovoid-elongated (FIG. 1 D-G), ovoid (FIG. 1 H), spherical (FIG. 1I) and frequently obpyriform (FIGS. 1 B-C). Sporangia with an elongated neck infrequently observed (FIG. 1 A). Sporangia mostly laterally attached to the main hyphae (FIGS. 1 A-F, I, J) with occasionally hyphal projections (FIG. 1 F). No basal plug was observed on empty sporangia. Sporangia averaged 41.3 ± 11.6 (range 25-87) × 28.3 ± 6.3 (range 17.5-40) μm (length × width) with a length:width ratio of 1.47. Direct germination of sporangia was occasionally observed.
2. Chlamydospores
Chlamydospores produced only in liquid culture, averaging 30 μm in diameter (range 25-37.5 μm).
3. Sex Organs
Homothallic with abundant oogonia on V8A within 5 days. Terminal oogonia, globose, and turn yellow when mature. Mean oogonial diameter was 29.3 ± 3 μm on V8A (range 22.5 to 35 μm). Predominantly tapered and occasionally coiled oogonial stalk. Oospores always spherical, markedly plerotic on V8A with an average diameter 26.2 ± 2.6 μm (range 20 to 30 μm). Average oospore wall thickness was 3.3 ± 0.7 μm. Antheridium attachment was lateral and sessile with short stalk, one per oogonium, attached always near the stalk, always paragynous, diclinous, usually club-shaped and occasionally cylindrical, averaging 11.4 ± 2.3 × 8.7 ± 1 μm.
4. Growth Temperatures
Optimum temperature for growth on V8A was 17.5° C (5.01 mm/d), with the upper temperature limit of 32.5° C and no growth at 5° C.
5. Growth Characteristics in Culture
On CMA submerged, with no aerial mycelia and distinct form (Fig 2 D); on MEA, V8A, and PDA dome shaped and faintly fluffy (Fig. 2A, B, C). Main hyphae averaged 4 μm thick (4-5 μm). No hyphal swellings were produced in liquid culture.
6. Distinguishing Characteristics
Being homothallic with paragynous antheridia and papillate sporangia, P. sp. ohioensis falls in Waterhouse Group I, which also includes P. cactorum, P. clandestina, P. idaei, P. iranica, P. italica, P. pseudotsugae and P. tentaculata. Morphologically, P. sp. ohioensis differs from P. cactorum by the absence of caducous and persistent ovoid or globose sporangia; from P. clandestina and P. iranica by absence of amphigynous antheridia and by sporangial features; from P. pseudotsugae and P. idaei by its thick-walled oospores, different sporangial shapes, and absence of amphigynous antheridia; from P. tentaculata by the absence of arachnoid antheridia and abundant chlamydospores. It differs from P. italica by its average larger oogonia, oospores, antheridial sizes and its different sporangial features and growth temperature relationship. P. sp. ohioensis can also be distinguished from P. hedraiandra by the absence of caducous sporangia, different sporangial shapes, absence of amphigynous antheridia, plerotic and thick-walled oospores, markedly tapered oogonial stalk and by different growth-temperature relationship.
P. sp. ohioensis can be distinguished from the phylogenetically related species in clade 4 based on morphological features. It can be differentiated from P. palmivora and P. megakarya by its homothallism and paragynous antheridia. It can be differentiated morphologically from P. quercina by its always spherical and thick-walled oospores, non-elongated oogonial shapes and markedly tapered oogonial stalk, plerotic oospores and its different growth-temperature relationship. Colony types on V8A, MEA, PDA and CMA resemble those of P. quercina but with faintly aerial mycelia and the absence of protuberances on hyphae. The sporangia of P. sp. ohioensis do not vary in shape and size as with P. quercina and are mostly ovoid-elongated or obpyriform with always one papilla per sporangium. P. sp. ohioensis can be separated from P. quercetorum by its mostly tapered oogonial stalk and plerotic, thick-walled oospores, distinct growth-temperature requirements, faintly fluffy dome shaped colony pattern on V8A, MEA and PDA, lack of a coralloid branching pattern, and its obpyriform or ovoid-elongated sporangia. P. sp. ohioensis can be separated from P. alticola by the absence of amphigynous antheridia, larger and plerotic oospores, absence of bipapillate and different sporangia shapes, different growth-temperature requirements and absence of hyphal swellings.
P. sp. ohioensis was associated with a declining mature white oak tree (Quercus alba)in Ohio.
This provisional species page was adapted from a draft manuscript kindly provided by Dr. Yilmaz Balci. His comments on this text and providing the pictures of morphological features are gratefully acknowledged.
Isolate list