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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).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 medicaginis E.M. Hans. & D.P. Maxwell 1991 (Oomycetes, Pythiales)
Phytophthora megasperma f. sp. medicaginis T.L. Kuan & Erwin 1980 Note: Forma specialis, no nomenclatural standing (Art. 4.N.3).Phytophthora sojae f. sp. medicaginis (T.L. Kuan & Erwin) M.A. Feris et al. 1989 Note: Forma specialis, no nomenclatural standing (Art. 4.N.3).
Notes: Previous to 1991, this species was commonly reported under the name Phytophthora megasperma.
Distribution: Cosmopolitan, throughout the range of the host.
Substrate: Roots.
Disease Note: Root rot, damping-off of seedlings.
Host: Medicago sativa (alfalfa), Onobrychis viciifolia (sainfoin), Cicer arietinum (chickpea) (Fabaceae). Also reported on Prunus mahaleb (cherry, Rosaceae).
Supporting Literature:
Crous, P.W., Phillips, A.J.L., and Baxter, A.P. 2000. Phytopathogenic Fungi from South Africa. University of Stellenbosch, Department of Plant Pathology Press, 358 pages.
Erwin, D.C., and Ribeiro, O.K. 1996. Phytophthora Diseases Worldwide. APS Press, St. Paul, Minnesota, 562 pages.
Faris, M.A., Sabo, F.E., Barr, D.J.S., and Lin, C.S. 1989. The systematics of Phytophthora sojae and P. megasperma. Canad. J. Bot. 67: 1442-1447
Hansen, E.M., and Maxwell, D.P. 1991. Species of the Phytophthora megasperma complex. Mycologia 83: 376-381
Kroon, L.P.N.M., Bakker, F.T., van den Bosch, G.B.M., Bonants, P.J.M., and Flier, W.G. 2004. Phylogenetic analysis of Phytophthora species based on mitochondrial and nuclear DNS sequences. Fungal Genet. Biol. 41: 766-782
Updated on Jun 12, 2006
P. medicaginis is classified in group V (Stamps et al. 1990) because of its production of nonpapillate sporangia and both paragynous and amphigynous antheridia. Spore morphology is shown in Figure 1, Figure 2 and Figure 3. See Tables 4.2 and 4.3 in Phytophthora Diseases Worldwide (Erwin and Ribeiro 1996) for tabular keys. Photomicrographs of hyphal swellings are shown in Figure 1, as well as paragynous and amphigynous antheridia on globose oogonia. Nonpapillate sporangium are shown in Figure 2, and a germinating oospore in Figure 3. Dimensions of sporangia, oogonia, antheridia, and oospores and cardinal temperatures for growth from different references are shown in Table 1. The cultural pattern of growth on potato-dextrose agar is shown in Figure 4.2 in Phytophthora Diseases Worldwide (Erwin and Ribeiro 1996).
1. Sporangia
Sporangia in aqueous solutions are ovoid to ellipsoid and nonpapillate (Figures 4.12L and 44.1 in Phytophthora Diseases Worldwide [Erwin and Ribeiro 1996]) and vary in size from 40 to 60 µm in length and 24 to 30 µm in width. A new sporangium may proliferate from within another sporangium. In some isolates, an inflated hyphal element forms at the base of the sporangium (Erwin 1965).
2. Chlamydospores and Hyphal Swellings
Hyphal swellings are frequently seen in aqueous cultures on infected plant tissue or vegetable juice agar plugs incubated in water (Erwin 1954, 1965) (Figure 4.4B in Phytophthora Diseases Worldwide (Erwin and Ribeiro 1996). Chlamydospores have been described in cultures that were incubated in soil and have been found among hyphal swellings. They were thin-walled and globular and varied from 6 to 16 µm in diameter; they also occurred singly, in chains, or in clusters on infected roots of alfalfa plants. Chlamydospores, hyphal swellings, and some portions of mycelium survived up to 7 months in soil at 5 to 30oC (Basu 1980). Z. A. El-Hamalawi (unpublished) noted chlamydospores while conducting a study of oospore germination (El-Hamalawi and Erwin 1986a), but they have not been readily producible in soil or media cultures (D. C. Erwin, unpublished).
3. Sex Organs
P. medicaginis is homothallic. Single-zoospore isolates produce oospores on V8 juice agar or other suitable media and in infected roots of alfalfa. Oogonia average 31 to 38 µm in diameter, and oospores average from 23 to 34 µm in diameter (Table 1). Oospore walls are about 2 to 4 µm thick. Oospores persist in a viable state from 4.5 months to 3.5 years (Table 5.3 in Phytophthora Diseases Worldwide (Erwin and Ribeiro 1996) (Pratt and Mitchell 1975; Stack and Millar 1985c).
Both amphigynous and paragynous antheridia are formed by single-zoospore cultures (Figure 4.26B and C in Phytophthora Diseases Worldwide [Erwin and Ribeiro 1996]). In some isolates, up to 91% of the antheridia are paragynous; in others, only 7% are paragynous (Erwin 1965). Percentages of paragynous antheridia in other studies are variable (12 to 100%) among several isolates (Hamm and Hansen 1982b) (Table 1). Oospores germinate to form sporangia (Figure 3) (Salvatorre et al. 1973; Stack and Millar 1985a–c; El-Hamalawi and Erwin 1986a, b).
4. Growth Temperatures
Growth is relatively slow (4 to 5 mm per day) on agar media and is optimal at 25 to 26oC. Little growth occurs at 5 or >33oC (Erwin 1954, 1966; E. M. Hansen and Maxwell 1991). Growth at 30oC is only slightly less than that at 24 to 27oC (Table 1).
[[PAPER:2372|1]]
Nomenclature information was provided by the the Systematic Botany and Mycology Laboratory in USDA-ARS.
Isolate list