Figure 1. Morphology of Phytophthora boehmeriae. Sporangia are papillate and sometimes bipapillate, and antheridia are amphigynous on globose oogonia. Mycelium is gnarled and grows in a tortuous manner. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

 

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

 

Figure 3. Papillate sporangia of Phytophthora boehmeriae. (Courtesy J. T. de Souza; Reproduced, by permission, from Dos Santos et al., 2006)

 

Figure 4. Oogonium of Phytophthora boehmeriae with an amphigynous antheridium and oospore (×1,000). (Courtesy Jean B. Ristaino)

 

Figure 5. Trunks of black wattle trees in Brazil showing symptoms of the gummosis complex caused by Phytophthora boehmeriae. (Courtesy J. T. de Souza; Reproduced, by permission, from Dos Santos et al., 2006) Click image to see larger view.

 

Introduction

Phytophthora boehmeriae  Sawada (1927)

 

Phytophthora boehmeriae was first isolated from the leaves of the Chinese silk tree Boehmeria nivea by Sawada in Taiwan in 1927 (Ho and Chang, 1992; Sawada, 1927). It also causes disease on paper mulberry and Deodar cedar (Zheng and Lu, 1989). It is classified as a group II species (Stamps et al., 1990) (Fig. 1).

Cultural Characteristics

Colonies are uniform and compact with well-defined margins and dense aerial mycelia (Fig. 2). The minimum temperature for growth is 5–6°C, the optimum temperature for growth is 25°C, and the maximum temperature for growth is 32°C. Mycelium is gnarled and grows in a tortuous pattern.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are sympodial.

 

Sporangia:

Sporangia are papillate and spherical, ovoid, ellipsoidal, obpyriform, or obturbinate. Mean sporangial measurements are 20–51 × 28–69 µm (Fig. 3). Sporangia are caducous with a short pedicel length of 5.0 µm or less (Stamps, 1978; Waterhouse, 1963). The average sporangia length–breadth ratio is 1.25–1.6.

 

Chlamydospores:

Chlamydospores are produced infrequently and are 26–52 µm (average 41 µm).

 

Sexual Structures

 

P. boehmeriae is homothallic and oospores form abundantly in host tissues.

 

Antheridia:

Antheridia are amphigynous, spherical, and 8–16 × 12.5–21 µm.

 

Oogonia:

Oogonia are smooth walled, hyaline to yellow, and 21.7–31.7 µm (average 28 µm). The oogonial stalk is not tapered.

 

Oospores:

Oospores form abundantly in host tissues with a diameter of 20.9–27.6 µm (average 25.1 µm) (Fig. 4).

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Acacia mearnsii

Black wattle

Gummosis

Brazil

Broussonetia papyrifera

Paper mulberry

Leaf spot

China

Cedrus deodara

Deodar cedar

Root rot

China

Citrus sinensis

Sweet orange

Brown rot

Argentina

Eucalyptus pilularis

Eucalyptus, black butt

Root rot

Australia

Gossypium spp.

Cotton

Boll blight

China

Gossypium hirsutum

Cotton

Boll rot

Greece

Pinus patula

Mexican yellow pine

Root rot

Australia

Symptoms

Symptoms are similar to those described for brown rot of citrus caused by P. citrophthora (Erwin and Ribeiro, 1996). The pathogen is splash dispersed and infects the fruit, causing a brown rot (Frezzi, 1941). Diseased tissue is firm and leathery. It also causes a leaf blight and root rot on a number of species and boll rot and blight on cotton. The pathogen causes trunk lesions and gummosis on black wattle (Dos Santos et al., 2006) (Fig. 5A and B).

References

Dos Santos, A. F., Luz, E. D. M. N., and de Souza, J. T. 2006. First report of Phytophthora boehmeriae on black wattle in Brazil. New Dis. Rep. 13:23. www.bspp.org.uk/ndr/.

 

Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

 

Frezzi, M. J. 1941. Phytophthora boehmeriae, the agent of brown rot of citrus fruits in the Argentine republic. Rev. Argent. Argon. 8:200-205.

 

Ho, H. H., and Chang, H. S. 1992. A re-evaluation of Phytophthora species described by K. Sawada in Taiwan. Mycotaxon 43:297-316.

 

Sawada, K. 1927. Descriptive catalog of the Formosan fungi III. Rep. Dep. Agric. Gov. Res. Inst. Formosa Bull. 27:1-62.

 

Stamps, D. J. 1978. Phytophthora boehmeriae. CMI Descr. Pathog. Fungi Bact. 591:1-2.

 

Stamps, D. J., Newhook, F. J., Waterhouse, G. M., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora de Bary. Mycol. Pap. 162. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.

 

Waterhouse, G. M. 1963. Key to the species of Phytophthora de Bary. Mycol. Pap. 92. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.

 

Zheng, X. B., and Lu, J. Y. 1989. Studies on the Phytophthora species in Fujian, Zhejiang, Jiangsu provinces and Shanghai, China. Acta Mycol. Sin. 8:161-168.