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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).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 trifolii E.M. Hansen & D.P. Maxwell 1991 (Oomycetes, Pythiales)
Phytophthora megasperma f. sp. trifolii R.G. Pratt 1981 Note: Formae speciales have no nomenclatural standing (Art. 4.n.3).
Notes: Previous to 1991, this species was commonly reported under the name Phytophthora megasperma.
Distribution: North America (USA: MS).
Substrate: Roots; sometimes shoots.
Disease Note: Severe stand-depleting root rot. Infection can extend up to the crown.
Host: Trifolium spp. (Fabaceae).
Supporting Literature:
Erwin, D.C., and Ribeiro, O.K. 1996. Phytophthora Diseases Worldwide. APS Press, St. Paul, Minnesota, 562 pages.
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. trifolii is classified in group V (Stamps et al. 1990). No photomicrographs are available in the literature. See Tables 4.2 and 4.3 in Phytophthora Diseases Worldwide (Erwin and Ribeiro 1996) for tabular keys.
The English diagnosis of P. trifolii follows (reproduced by permission from Mycologia 83:376–381, E. M. Hansen and Maxwell, copyright 1991, The New York Botanical Garden, Bronx, New York):
Homothallic, producing oospores in single strain culture, with predominantly paragynous antheridia. Oogonia 43 µm (37–46 µm) diam, oospores 33–37 µm diam. Sporangia formed in liquid culture, ovoid to ellipsoid, nonpapillate, 44–50 µm long by 30–35 µm wide. Slow growing on agar media, about 3–4 mm/day at 25C, no growth at 35C. Colony dense, tufted, patternless. Pathogenic on arrowleaf clover, Trifolium vesiculosum Savi, and other Trifolium species. Named for the principal host. Holotype materials are deposited at the Oregon State University herbarium. Cultures are on file at the American Type Culture Collection.
On carrot agar, oogonia of P. trifolii average 43 µm diam. Sporangia formed on colonies grown in pea broth are smaller (44 µm in length) than other species of the P. megasperma complex. The combination of relatively short sporangia and larger oogonia is distinctive. Growth rate is slow (3–4 mm/day at 25C), and optimal between 20 and 25C. No growth occurred at 30C. Colonies exhibit dense, patternless growth on carrot agar, often with a tufted appearance. The fungus is sensitive to metalaxyl on cornmeal agar, with no growth at 1 mg/liter (E. M. Hansen and Hamm, 1983).
Isolates of P. trifolii have a unique protein pattern with SDS PAGE (polyacrilamide gel electrophoresis) and isozyme analysis (Nygaard et al., 1989). Thus, they are readily distinguished from other isolates of the P. megasperma complex. There are 11–15 metaphase chromosomes in oogonia, which is similar in number to P. sojae and P. medicaginis (Hansen et al., 1986).
1. Sporangia
Sporangia are ovoid to slightly obpyriform (R. G. Pratt 1981) and average 49.3 µm in length; the length-breadth ratio is 1.4:1 (E. M. Hansen and Hamm 1983).
2. Hyphal Swellings
Hyphal swellings have not been described.
3. Chlamydospores
Chlamydospores have not been described.
4. Sex Organs
Oogonia form in single culture (homothallic), are globose, and measure 21 to 51 µm in diameter (R. G. Pratt 1981). E. M. Hansen and Hamm (1983) report an average of 44.9 µm. A majority of the antheridia are paragynous, but some are amphigynous.
5. Growth Temperatures
Growth is optimal at 22.5oC, and no growth occurs at 5, 35 (E. M. Hansen and Hamm 1983), or 30oC (E. M. Hansen and Maxwell 1991). Growth at 25oC is relatively slow (0.5 cm per day on V8 juice agar) (R. G. Pratt 1981).
6. Distinguishing Characteristics
P. trifolii grows optimally at a lower temperature (22.5oC) and has larger oogonia (44.9 µm in diameter) and shorter sporangia (43.9 µm) than P. medicaginis and P. sojae. There are few gross differences in morphology among the three species, however. Growth of all three species is inhibited by metalaxyl (1 µg/ml), but only 44% inhibition is reported for DF (isolates of Douglas fir) and ALF2 (large-oogonia isolates of P. megasperma from alfalfa) (E. M. Hansen and Hamm 1983).
Nomenclature information was provided by the the Systematic Botany and Mycology Laboratory in USDA-ARS.
Isolate list