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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).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 mengei G.T. Brown, M.E. Gallegly & C.X. Hong 2009 (Oomycetes, Pythiales)
Distribution: North America (USA: CA).
Substrate: Trunks, roots, fruits.
Disease Note: Canker.
Host: Persea americana (Lauraceae).
Supporting Literature:
Hong, C.X., Gallegly, M.E., Browne, G.T., Bhat, R.G., Richardson, P.A., and Kong, P. 2009. The avocado subgroup of Phytophthora citricola constitutes a distinct species, Phytophthora mengei sp. nov. Mycologia 101: 833-840.
Updated on Nov 17, 2009
Phytophthora mengei G.T. Browne, M.E. Gallegly & C.X. Hong historically has been considered part of the P. citricola species complex. Hong et al. (2009) confirmed this taxon as a distinct species that is phylogenetically in clade 2c basal to P. siskiyouensis.
1. Sporangia
When placed in water or soil extract, mycelia on lima bean agar disks from 3 d old cultures form abundant semipapillate sporangia in fewer than 8 h under fluorescent light at room temperature. The apical thickened area is 2.4–3.4 µm deep. Bizarre shapes of sporangia occur (sickle, boomerang, sombrero and bluntly ellipsoid). Bluntly ellipsoid sporangia, sometimes with a constriction in the middle, average about 95 X 35 µm. Smaller ovoid sporangia are about 49 X 34 µm. Overall sporangia average 62.7 X 35.2 µm (range 37.4–95.0 X 27.2– 44.2 µm). The length to width ratio is 1.8. Width of the papillae pores vary, 6.6–13.5 µm. Sporangia are noncaducous. Also a few sporangia are formed on lima bean agar where they are mostly ovoid and of about the same size as the ovoid ones formed in water, but those formed in agar sometimes appear to be papillate. Empty sporangia have a small plug at the point of pedicel attachment. Simple sympodia occur but sometimes a single sporangium on a long pedicel is seen.
2. Chlamydospores
Hyphal swellings and chlamydospores have not been seen, but knobby hyphae are common.
3. Sex Organs
Phytophthora mengei is homothallic and forms sex bodies readily in lima bean and hemp-seed agars. The oogonia average 24.0 µm diameter (range 20.4–27.2 µm) and some have tapered stalks, sometimes with a slight hook in the taper. Oospores are mostly plerotic with 2.3 µm thick walls (range 1.5– 3.0 µm) and average 21.7 µm diameter (range 18.7– 24.5 µm). Oospores in tapered oogonia appear aplerotic as the taper draws away from the round oospores. The diclinous antheridia are paragynous and commonly asymmetrically capitate. The end of the club is approximately 10 µm diameter. On tapered oogonia the antheridia are located on the taper, commonly at the bottom.
4. Growth Temperatures
Thus the minimum temperature for colony growth was 6–10° C, the optimum about 25° C, and the maximum 30–33° C.
5. Growth Characteristics in Culture
6. Distinguishing Characteristics
Morphologically similar species are P. citricola, P. syringae, P. pseudosyringae, P. primulae and P. porri. Based on its original description P. siskiyouensis will be placed in this group. The differences of these species are that P. mengei has smaller oogonia, no hyphal swellings, and has asymmetric capitate antheridia on many of the oogonia. The sporangia of P. mengei are similar to those of P. primulae and differ from those of the other species in the group by forming many large, bizarre shapes. However the oogonia of P. mengei are much smaller than those of P. primulae (24 vs. 38 µm) and the maximum temperature for colony growth is higher (31 vs. , 27° C). This new species also can be easily separated from P. capsici and P. tropicalis. Phytophthora mengei is homothallic and produces noncaducous semipapillate sporangia, whereas P. capsici and P. tropicalis are heterothallic and produce conspicuously papillate sporangia. In addition sporangia of P. tropicalis are caducous with long pedicels. P. mengei and P. siskiyouensis are mostly similar morphologically. The oospores of P. mengei are plerotic, whereas those of P. siskiyouensis are aplerotic. Also the oogonial sizes of these two species differ slightly (26.0 vs. 27.8 µm). The antheridia of P. mengei and those of P. siskiyouensis are described respectively as being asymmetrically capitate and capitate. Also sporangia of these two species are similar but those of P. mengei appear to be more irregularly shaped. The maximum growth temperature for P. mengei is slightly higher than that for P. siskiyouensis, whereas the minimum temperature for growth is lower for P. siskiyouensis. Variability among isolates of these two species could render the above discussion moot.
This pathogen is found in the trunks, main structural roots and fruit of infected avocado trees in southern California, USA.
Hong, C. X., Gallegly, M. E., Browne, G. T., Bhat, R. G., Richardson, P. A., Kong, P. 2009. The avocado subgroup of Phytophthora citricola constitutes a distinct species, Phytophthora mengei sp. nov. Mycologia 101:833–840
This species page was adapted from Hong et al. (2009)
Isolate list