Introduction
Phytophthora trifolii E. M. Hansen & D. P. Maxwell (1991)
Phytophthora trifolii
was first identified as
P. megasperma
f. sp. trifolii by R. G. Pratt (1981)
to distinguish it from species that attack soybean and alfalfa.
Prior to 1991, the species was referred to as P. megasperma.
The English diagnosis of the species can be found in Hansen and Maxwell (1991).
P. trifolii causes severe loss of stands of arrowleaf clover (Trifolium
vesiculosum) in
Cultural Characteristics
The optimum temperature for growth is 22.5°C (Hansen and Hamm, 1983).
No growth occurs at 5, 30, or 35°C.
Reproductive Structures
Asexual Structures
Sporangia:
Sporangia are ovoid to slightly obpyriform, nonpapillate, and noncaducous and have an average length of 49.3 µm (Pratt, 1981). The length–breadth ratio is 1.4:1. P. trifolii has smaller sporangia than P. medicaginis or P. sojae (Gallegly and Hong, 2008) (Fig. 1).
Chlamydospores and Hyphal Swellings:
Chlamydospores and hyphal swellings have not been described.
Sexual Structures
P. trifolii is a homothallic species.
Antheridia:
The majority of antheridia are paragynous but some amphigynous antheridia have been reported.
Oogonia:
Oogonia are globose, large, and 21–51 µm in diameter (average 44.9 µm) (Hansen and Hamm, 1983; Pratt, 1981). P. trifolii has larger oogonia than P. medicaginis or P. sojae.
Oospores:
Oospores are 33–37 µm in diameter and golden brown. Oogonia contain plerotic to aplerotic oospores (Fig. 2).
Host Range and Distribution
|
Host |
Common Name |
Disease |
Geographical Distribution |
|
Trifolium agrarium |
Hop clover |
Root rot |
|
|
Trifolium incarnatum |
Crimson clover |
Root rot |
|
|
Trifolium repens |
White clover |
Root rot |
|
|
Trifolium subterraneum |
Subterranean clover |
Root rot |
|
|
Trifolium vesiculosum |
Arrowleaf clover |
Root rot |
|
Symptoms
Root Rot of
Trifolium vesiculosum (Arrowleaf Clover):
Root rot occurs in poorly drained areas. Symptoms include roots that are red-brown, stems that turn red and loose their leaves, and leaves that are chlorotic or necrotic. A distinct margin between healthy and diseased tissue can be found in longitudinally split roots, and the disease frequently extends into the crown of the plants (Erwin and Ribeiro, 1996).
References
Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.
Gallegly, M., and Hong, C. 2008. Phytophthora: Identifying Species by Morphology
and DNA Fingerprints. American Phytopathological Society,
Hansen, E. M., and
Hansen, E. M., and Maxwell, D. P. 1991. Species of the
Phytophthora megasperma complex. Mycologia 83:376-381.
Pratt, R. G. 1981. Morphology, pathogenicity, and host range of
Phytophthora megasperma, P.
erythroseptica, and P. parasitica
from arrowleaf clover. Phytopathology 71:276-282.
Stamps, D. J., Waterhouse, G. M., Newhook, F. J., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora. Mycol. Pap. 162. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.