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Figure 1. Morphology of Phytophthora porri. Upper row, Semipapillate sporangia; globose chlamydospores. Lower row, Globose oogonia with either paragynous (left) or amphigynous (right) antheridia. Oospore wall is 3–4.5 µm thick. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

Figure 2. Culture of Phytophthora porri grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

Introduction

Phytophthora porri  Foister (1931)

 

Phytophthora porri was first isolated from diseased leek plants (Allium porrum) in Scotland by Foister (1931). It was first reported from North America on stored carrots (Ho, 1983; Stelfox and Henry, 1978). The species from leek and cabbage had differences in growth temperatures, morphological characters, and RFLP patterns of mitochondrial DNA, suggesting that the Brassica isolates may be a different species (de Cock et al., 1992; Gallegly and Hong, 2008). P. porri is a group III Phytophthora species (Stamps et al., 1990) (Fig. 1).

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	United States, Japan, Netherlands
Brassica oleracea var. capitata	White cabbage	White tip; storage, crown, root, and collar rot	Germany, United Kingdom
Campanula persicifolia	Willow bellflower	Crown rot	United Kingdom
Daucus carota	Carrot	Root rot	Germany, Canada
Dianthus caryophyllus	Carnation	Collar rot	Greece
Gladiolus spp.	Sword lily	Collar and bulb rot	Greece
Hyacinthus orientalis	Hyacinth	Leaf blight	Japan
Tulipa gesneriana	Tulip	Blight; rot	Japan

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, St. Paul, MN.

 

Ho, H. H. 1983. Phytophthora porri from stored carrots in Alberta. Mycologia 75:747-751.

 

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 Alberta. Can. Plant Dis. Surv. 58:87-91.