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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).
[ Click the tree to enlarge it. ]
P. taxon emzansi has been designated only as an informal taxon and not as a new species. Only two isolates were available, both from the same host plant. Furthermore, while the properties of the taxon appear to be unique, the morphological characteristics of the two P. taxon emzansi isolates demonstrated a number of instabilities and inconsistencies, including variable growth rate and colony morphology, a high degree of plasticity in sporangial morphology, high levels of zygotic abortion (42 %) and poorly developed gametangia. Similar aberrant features were noted in the hybrid species P. alni and its variants by Brasier et al. (2004). The aberrant morphological features in P. taxon emzansi suggest some genetic instability. Evidence of this genetic instability was not found in any of the three nuclear or two mitochondrial gene regions that were sequenced, since the sequences of these gene regions were identical in both isolates.
1. Sporangia
Sporangia are semi-papillate, non-caducous, non-proliferating and single or occasionally formed in loose sympodia. They are very variable in size and shape ranging from an elongated wine-glass form, with smooth to slightly wavy sides or bent top, to ovoid sometimes having a ‘pinched’ area above the broadest part of the base resulting in a sac-like shape, or occasionally slightly peanut- or kidney-shaped. Most were single lobed (rarely bi-lobed) and attached centrally but a proportion (37.5 %) had an eccentric (off set) attachment. The dimensions of sporangia range from (length) 35–67.5 μm (mean 49.6 μm; SD 8.6 μm) by (breadth) 17.5–47.5 μm (mean 27.4 μm; SD 5.7 μm). The length : breadth ratio is 1.8–1.9, exit pore width ranges from 5–7.5 μm and the diameter of encysted zoospores ranges from 10–15 μm.
2. Chlamydospores
No chlamydospores or hypal swellings observed.
3. Sex Organs
Antheridia are amphigynous, paragyny is very rare. Antheridia are single-celled, large and range from ball to block shaped, the length ranges from 10–20 μm (av. 14.5 μm; SD 2.1 μm) and width between 12.5–17.5 μm (av. 14 μm; SD 1.4 μm). Oogonia are round, the diameter ranges from 25–37.5 μm (mean 30.7 μm, SD 3.1 μm) and they are formed on the terminal ends of hyphae. Frequently a tapering oogonial stalk can be seen through empty antheridia. Between 54 – 58 % of oogonia mature to form oospores, the other 42 – 46 % of oospores aborted or did not mature. Aborted oogonia often developed abnormal forms. A mixture of plerotic and aplerotic oospores form in mature oogonia (53 : 47 plerotic : aplerotic) and mature oospores tend towards being thin-walled (< 2.5 μm). The average oospore diameter is 27.9 μm (SD 2.6 μm) covering a range between 22.5–32.5 μm.
4. Growth Temperatures
Cardinal temperatures: minimum 10 °C, optimum 20 °C, maximum 27.5 °C and lethal temperature 30 °C. Daily growth rate at 20 °C was 5 mm per day.
5. Growth Characteristics in Culture
The colony morphology on CA included a loose chrysanthemum pattern and woolly petaloid pattern. The hyphae are on average 6–7.5 μm diameter and have developed a moderate number of short branches (a similar degree of branching to that depicted for P. syringae in Erwin & Ribeiro 1996). Low levels of aerial mycelium were produced at the lower temperature spectrum (5–22.5 °C) but this increased to a moderate amount at 25–27.5 °C.
6. Distinguishing Characteristics
Phytophthora taxon emzansi was clearly different to the other taxa in the P. citricola complex because the attachment of the antheridia to the oogonia was amphigynous, whereas all other taxa had paragynous antheridia. Antheridia of P. taxon emzansi were also significantly bigger (on average 14 × 14.5 μm) than those of the other species in the complex and they had longer antheridial stalks. Oogonia of P. taxon emzansi also had high levels of zygotic abortion (42 – 46 %); low oogonia maturity (54 – 58 %) and high levels of deformed oogonia compared with the other species.
P. taxon emzansi is associated with A. betulina but is non-pathogenic towards this host.
Bezuidenhout, C. M., Denman, S., Kirk, S. A., Botha, W.J., Mostert, L., McLeod, A. 2010. Phytophthora taxa associated with cultivated Agathosma, with emphasis on the P. citricola complex and P. capensis sp. nov. Persoonia 25: 32– 49.
Brasier CM, Kirk SA, Delcan J, Cooke DEL, Jung T, Man in ‘t Veld, WA. 2004. Phytophthora alni sp. nov. and its variants: designation of emerging heteroploid hybrid pathogens spreading on Alnus trees. Mycol. Res. 108: 1172–1184.
Erwin DC, Ribeiro OK. 1996. Phytophthora diseases worldwide. The American Phytopathological Society APS, St. Paul, Minnesota, USA.
This species page was adapted from Bezuidenhout et al. (2010). Comments on the content of this page by Dr. A. McLeod are gratefully acknowledged.
Isolate list