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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).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 foliorum Donahoo & Lamour 2006 (Oomycetes, Pythiales)
Distribution: North America (USA: CA, TN).
Substrate: Leaves.
Disease Note: Leaf spots.
Host: Rhododendron spp. (Ericaceae).
Supporting Literature:
Donahoo, R., Blomquist, C.L., Thomas, S.L., Moulton, J.K., Cooke, D.E.L., and Lamour, K.H. 2006. Phytophthora foliorum sp. nov., a new species causing leaf blight of azalea. Mycol. Res. 110: 1309-1322.
Updated on Mar 11, 2008
Phytophthora foliorum Donahoo & Lamour was initially recovered from azalea leaves during a nursery survey for the quarantine pathogen P. ramorum. Due to similarities in the primer annealing sites with the ITS primers of the P. ramorum conventional molecular diagnostic marker used at the time P. foliorum would give a false positive unless the amplicon was digested with particular restriction enzymes. Phylogenetically it is a clade 8c species related to P. ramorum, P. hibernalis and P. lateralis.
1. Sporangia
Sporangia are semipapillate and are on average 51 X 34 µm. Sporangia are deciduous with short pedicels (<5–20 µm). Sporangia were only produced in soil extract water and rarely, if ever, are produced in culture.
2. Chlamydospores
No chlamydospores produced.
3. Sex Organs
Species homothallic; oospores abundantly produced in culture. Oogonia not ornamented, 37 µm average diameter (32– 43 µm range). Oospores plerotic, spherical, 33 µm average diameter (range 28–38 µm). Antheridia mostly paragynous and usually attached to the oogonia next to the oogonial stalk.
4. Growth Temperatures
Growth on CMA between 3–28° C. Optimum growth at 18–22° C at a rate of 3mm/d on V8 agar.
5. Growth Characteristics in Culture
Growth on V8 and CMA was appressed whereas on PDA, growth was aerial and cottony
6. Distinguishing Characteristics
P. foliorum resembles P. cactorum in culture, but in culture P. cactorum is distinguished from P. foliorum by its rapid growth at higher temperatures (i.e., >24° C) and production of sporangia. P. foliorum is morphologically somewhat similar to P. syringae in culture, yet is distinguishable by sporangia being cauducous and born terminally, whereas for P. syringae sporangia are persistent, and form in succession in a close monochasial sympodium formation. At all temperatures, P. foliorum had a greater growth rate than P. ramorum and P. hibernalis. P. foliorum isolates grew faster in total darkness than with a photoperiod. The growth rate of isolates on CMA at 21° C was found to be reduced by 60% when isolates were exposed daily to a 12 h photoperiod (Donahoo et al. 2006).
Morphologically, P. foliorum is distinct from its sister taxa (P. ramorum, P. lateralis, and P. hibernalis). P. foliorum differs from P. ramorum in that it is homothallic and rarely if ever produces sporangia in culture. P. foliorum differs from P. lateralis in that it has semi-papillate sporangia. Unlike P. lateralis and P. ramorum, P. foliorum has not been found to produce chlamydospores. P. foliorum was discovered simultaneously in California and Tennessee during state and national surveys to detect the sudden oak death pathogen P. ramorum.
P. ramorum is a quarantine pathogen and a nested PCR assay designed to amplify a unique portion of the P. ramorum ITS is one of the molecular diagnostic procedures that has been used to screen plant material. Alignment of the outer and inner P. ramorum nested PCR primers with the P. foliorum ITS sequence indicates that the corresponding sequences differ by one to two bases for each of the primers in the first and second rounds of PCR. Cross-reactivity of this newly-described species illustrates one of the risks in using DNA-based diagnostics as the sole means of detecting a specific pathogen. Short of subsequent restriction digest on the resulting nested amplicon the current P. ramorum nested PCR detection assay can lead to false-positives.
P. foliorum is pathogenic on both wounded and intact azalea leaves.
Donahoo, R., Blomquist, C. L., Thomas, S. L., Moulton, J. K., Cooke, D. E. L., Lamour, K. H. 2006. Phytophthora foliorum sp. nov., a new species causing leaf blight of azalea. Mycol. Res. 110:1309-1322.
This species page was adapted from Donahoo et al. (2006).
Isolate list