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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).
[ Click the tree to enlarge it. ]
Phytophthora fallax Dobbie & M. A. Dick, was recovered from plantation Eucalyptus trees in New Zealand exhibiting a crown disease. Phylogenetically it is in clade 9 closely related to P. captiosa.
1. Sporangia
Sporangia produced in pea broth (48 h), or on host petiole material floated in soil water, are non-papillate, non-caducous, obpyriform to distorted, often with a distinctive elongated neck and conspicuous basal plug. Dimensions average 55.5 ± 5 x 32 ± 3 µm with isolate means between 50.5–61.5 x 28–34 µm (holotype 52 ± 8 x 32.5 ± 5 µm). Length/breath ratio is about 1.7. Hyphal projections are often seen at the apex of mature sporangia. Sporangia proliferate both internally and externally from the base of an existing sporangium.
2. Chlamydospores
Spherical, terminal chlamydospores measuring 12–26 µm diameter were produced in soil water in two isolates (including the holotype). No hyphal swellings were observed.
3. Sex Organs
Phytophthora fallax is homothallic, gametangia develop in the host tissue and are produced abundantly on CA within 30 d. Oogonia are spherical, often becoming pale brown with age. Measurements from nine isolates averaged 33.5 ± 3 µm, with isolate means ranging from 30–39 µm (holotype 33 ± 3 µm). Antheridia both amphigynous and paragynous. The structure is often difficult to determine on account of the coiled and distorted hyphae around the stalk of the oogonia, and it is speculated that the obscured antheridia are most likely to be paragynous. If this is the case five of the nine isolates examined had equal numbers of amphigynous and paragynous antheridia, two had predominantly paragynous antheridia (including the holotype) and two had predominantly amphigynous antheridia. In four of these isolates antheridia were occasionally absent. The lack of antheridia was observed only in older cultures (over four years old) and it is thought that this characteristic in P. fallax is storage-related. Amphigynous antheridia are cylindrical, single celled, and average 18.5 ± 4 x 14 ± 1 µm (holotype 23 ± 7 x 12.5 ± 0.7 µm). Paragynous antheridia are globose, and average 9 ± 2 µm (holotype 8 ± 2 µm), most often attached near the stalk. Oospores are initially plerotic, becoming aplerotic with age, and average 31.5 ± 2.5 µm, with isolate means ranging from 29–35 µm (holotype: 29.5 ± 3 µm). The oospore wall averages 2 ± 0.5 µm thick. Oogonia and antheridia formed in host tissue are brown.
4. Growth Temperatures
Phytophthora fallax grows slowly on CA at 20° C in the dark at approximately 3.7 mm/d, (the range for eight isolates was from ca 2.9 – 5.7 mm/d (holotype: approximately 3.1 mm/d). On CA minimal growth was seen at 2° C, the optimum at ca 20° C, minimal growth was seen at 27° C. Two isolates had minimal growth at 28° C and growth ceased at 30° C.
5. Growth Characteristics in Culture
Colonies after 10 d at 20° C in the dark are stellate to rosaceous, often with densely fluffy mycelium.
6. Distinguishing Characteristics
Being homothallic with amphigynous or paragynous antheridia and non-papillate sporangia, Phytophthora fallax falls in Groups V and VI of the traditional morphological classification, while its ITS rDNA sequence indicates a greater phylogenetic relatedness to P. captiosa and to Phytophthora species in ITS clades 9 and 10 (including P. insolita, P. macrochlamydospora, and P. richardiae). It is distinguished from other species in groups V and VI of Waterhouse’s classification system by its combination of both amphigynous and paragynous antheridia and its often distorted sporangia. Among the species grouped together on the phylogenetic tree P. fallax most closely resembles P. richardiae and P. captiosa. It is distinguished from these species by the occurrence of paragynous antheridia and the presence of distorted sporangia. Also it can be distinguished from P. richardiae by a lower minimum growth temperature and from P. captiosa by its rather different growth–temperature responses.
P. fallax, causes crown disease of from E. delegatensis, E. fastigata, E. nitens and E. regnans.
Dick, M. A., Dobbie, K., Cooke, D. E. L., Brasier, C. M. 2006. Phytophthora captiosa sp. nov. and P. fallax sp. nov. causing crown dieback of Eucalyptus in New Zealand. Mycol. Res. 110:393-404.
Nomenclature information was provided by the the Systematic Botany and Mycology Laboratory in USDA-ARS. This species page was adapted from Dick et al. (2006)
Isolate list