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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).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 irrigata C. Hong & M. Gallegly 2008 (Oomycetes, Pythiales)
Notes: The nature of the type is uncertain.
Distribution: USA.
Supporting Literature:
Hong, C., Gallegly, M.E., Richardson, P.A., Kong, P., and Moorman, G.W. 2008. Phytophthora irrigata, a new species isolated from irrigation reservoirs and rivers in Eastern United States of America. F.E.M.S. Microbiol. Lett. 285: 203-211.
Updated on Mar 04, 2011
Phytophthora irrigata C. Hong and M. Gallegly was recovered from irrigation water reservoirs at ornamental plant nurseries in Virginia. It is in clade 9 with P. fallax and P. captiosa as the closest relatives.
1. Sporangia
Sporangia are formed overnight in the nine isolates when discs from 3-day-old cultures on lima bean agar are placed in 10% soil extract under cool white fluorescent lamps at 1.5Wm2 (100 ft candles). Some isolates release zoospores almost as soon as sporangia are produced. The sporangia are uniform in shape and relatively small. The shape varies from spheroid to obpyriform but is predominantly ovoid (34.0–51.0 by 27.2–41.5 µm) averaging 43.5 by 33.2 µm with a length to width ratio of 1.3. The sporangia are formed mostly on long sporangiophores and are nonpapillate as well as noncaducous. Internal proliferation and nesting occur.
2. Chlamydospores
No chlamydospores formed
3. Sex Organs
Heterothallic and all nine isolates examined were A1 compatibility type. Within 1 month of the onset of mating tests, oospores produced by P. irrigata were observed in Petri dishes when paired with A2 isolates of P. capsici, P. cinnamomi, and P. meadii, but not in those paired with A1 isolates of the same species, regardless of the medium. Further, selfed sexual organs are formed by P. irrigata isolates when P. capsici and P. cinnamomi A2 isolates were used in the polycarbonate procedure. The size of oogonia varied from 30.6 to 51.2 µm in diameter (average 42.4 µm). Oospores are plerotic and average 39.5 µm in diameter. The oospore walls are 2.8–3.0 µm thick. Antheridia are amphigynous; in one isolate they are small and round or slightly flattened, averaging about 10 µm, whereas they are larger and slightly flattened in the other isolates (16.2 µm tangential and 10.2 µm perpendicular to the oogonial walls). In addition to being golden brown in hemp seed agar, some oogonia are encrusted with a brown pigment.
4. Growth Temperatures
The optimum temperature for growth of P. irrigata was 30° C and produced a trace of growth at 40° C and no growth at 5° C.
5. Growth Characteristics in Culture
The pattern of colony growth on potato dextrose agar is petaloid, but there is no pattern on lima bean agar. The mycelium in young cultures is very uniform with no swellings, knobs, or chlamydospores; hyphae are relatively narrow at about 5.0 µm wide.
6. Distinguishing Characteristics
Phytophthora irrigata can be distinguished from the 33 other nonpapillate species of Phytophthora including Phytophthora alni and P. inundata, P. captiosa and P. fallax, Phytophthora europaea and Phytophthora uliginosa, P. pistaciae, P. polonica, and P. melonis by sexual pattern, morphology, and maximum growth temperature. Phytophthora irrigata is heterothallic. It can be easily separated from 24 homothallic species that readily produce oospores in host tissues or in agar media. Phytophthora drechsleri, P. inundata, and P. melonis are three heterothallic, nonpapillate species that grow well at 35° C. Phytophthora irrigata is a fourth species to be added to this group. It differs from the other three by having much smaller sporangia, which liberate zoospores immediately after sporangia are formed. Also, P. irrigata produces fully plerotic oospores whereas the other three produce aplerotic to slightly aplerotic oospores. The mycelium of P. irrigata is uniform with no swellings, knobs, or chlamydospores, which occur in the other three species.
Phytophthora irrigata is pathogenic to azaleas and some vegetables such as tomato, pepper, and eggplant.
Hong, C., Gallegly, M. E., Richardson, P. A., Kong, P., Moorman, G. W. 2008. Phytophthora irrigata , a new species isolated from irrigation reservoirs and rivers in Eastern United States of America. FEMS Microbiol. Lett. 285:203–211
This species page was adapted from Hong et al. (2008).
Isolate list