Introduction
Phytophthora porri
Foister (1931)
Phytophthora porri
was first isolated from diseased leek plants (Allium
porrum) in
Cultural Characteristics
The minimum temperature for growth is 3°C, the optimum temperature for growth is
18–25°C, and the maximum temperature for growth is 27°C (de Cock et al., 1992)
(Fig. 2). Oogonia are produced at 10°C.
Reproductive Structures
Asexual Structures
Sporangiophores:
Sporangiophores are undifferentiated and often have intercalary swellings.
Sporangia:
Sporangia are obpyriform, ovoid, ellipsoid, and sometimes distorted in shape. Sporangia are 10–52 × 17–82 µm. Sporangia are semipapillate, noncaducous, nonproliferating, and borne successively (Fig. 1).
Chlamydospores:
Chlamydospores are 20.8–35.3 µm in diameter (average of 30.0 µm) and form after prolonged incubation in water (Fig. 1).
Hyphae:
Hyphae are up to 8 µm in diameter but are not uniform. Coiling of mycelium in water culture is common (Gallegly and Hong, 2008). Hyphal swellings can be round, ellipsoid, or angular and occur singly or in chains.
Sexual Structures
P. porri is homothallic.
Antheridia:
Antheridia are predominantly paragynous and oblique to the oogonial wall. Multiple antheridia can occur on an oogonium. Amphigynous antheridia have also been observed.
Oogonia:
Oogonia are globose and average about 34 µm in diameter. According to de Cock et al. (1992), most oogonia are abortive.
Oospores:
Oospores are globose, spherical, aplerotic, and 28–30 µm in diameter (Fig. 1).
Host Range and Distribution
For a wider range of host species refer to Table 53.1 in Erwin and Ribeiro (1996).
Host |
Common Name |
Disease |
Geographical Distribution |
Allium spp. |
Shallot, scallion, onion, leek, garlic, chive |
Leaf blight and shanking; white tip; storage, crown, root, and collar rot |
|
Brassica oleracea var. capitata |
White cabbage |
White tip; storage, crown, root, and collar rot |
|
Campanula persicifolia |
|
Crown rot |
|
Daucus carota |
Carrot |
Root rot |
|
Dianthus caryophyllus |
Carnation |
Collar rot |
|
Gladiolus spp. |
Sword lily |
Collar and bulb rot |
|
Hyacinthus orientalis |
Hyacinth |
Leaf blight |
|
Tulipa gesneriana |
Tulip |
Blight; rot |
|
Symptoms
White Tip of
Allium porrum (Leek):
Leaf tips of leek turn yellow and color extends for several centimeters down the
leaf blade. The affected leaves die
rapidly and turn white, giving the disease its name “white tip” (Foister, 1931).
Leaves may be distorted or twisted.
Infection in early development leads to stunted plants, while infection in older
plants results in rapid wilt or breakage of the stem at the soil line.
The disease develops in damp, humid weather.
Infection known as shanking occurs when bulbs of onions and shallots in soil are affected and the pathogen spreads through the roots. The pathogen can also cause a storage rot of carrot (Stelfox and Henry, 1978).
References
de Cock, A. W. W. M., Neuvel, A., Bahnweg, A., de Cock, J. C. J. M., and Prell, H. H. 1992. A comparison of morphology, pathogenicity, and restriction fragment patterns of mitochondrial DNA in isolates of Phytophthora porri Foister. Neth. J. Plant Pathol. 98:277-289.
Erwin D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.
Foister, C. E. 1931. The white tip disease of leeks and its casual fungus, Phytophthora porri n. sp. Trans. Proc. Bot. Soc. Edinburgh 30(4):257-281.
Gallegly, M., and Hong, C. 2008.
Phytophthora: Identifying Species by Morphology and DNA Fingerprints.
American Phytopathological Society,
Ho, H. H. 1983.
Phytophthora porri from stored carrots in
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.
Stelfox, D., and Henry, A. W. 1978. Occurrence of the rubbery brown rot of
stored carrots in