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Figure 1. Morphology of Phytophthora heveae. Papillate sporangia with various shapes often form laterally on sporangiophores. Globose oogonium (lower left) with an amphigynous antheridium; oospore is globose and often aplerotic. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

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

Figure 3. Germinated oospore of Phytophthora heveae with two terminal sporangia. (Used, by permission, from North Carolina State University, Department of Plant Pathology Slide Collection)

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

Figure 5. Blight on leaves of Brazil nut caused by Phytophthora heveae. (Courtesy Jose Emilson Cardoso; Reproduced, by permission, Cultivo do Cajueiro, Embraba Agroindustria Tropical, Brazil)

Introduction

Phytophthora heveae  A. W. Thompson (1929)

 

Phytophthora heveae was first described by Thompson in 1929 as the cause of black stripe disease on Hevea (rubber) plantations in Malaysia (Thompson, 1929). It was first believed to be confined to Malaysia, but the geographic range has increased with international trade to include Brazil, Australia, Guatemala, New Zealand, and on other hosts, the United States. The pathogen was named P. palmivora var. heveae (A. W. Thompson) by Orellana in 1959 (Cline et al., 2008; Orellana, 1959). P. hevea resembles P. katsurae except for the non-ornamented oogonial walls (Stamps, 1978). It is a group II Phytophthora species (Stamps et al., 1990; Waterhouse, 1963) (Fig. 1). 

Cultural Characteristics

The minimum temperature for growth is 11.5°C, the optimum temperature for growth is 25°C, and the maximum temperature for growth is 31.0–32.5°C (Fig. 2). P. heveae does not produce aerial mycelium.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophore branching is irregular and the sympodium is simple. Intercalary swellings are often present.

 

Sporangia:

Sporangia are papillate with a conspicuous apical thickening (5 µm in diameter) (Fig. 3). Sporangia are irregularly shaped, obpyriform to ellipsoidal, and often asymmetrical and form lateral stalks. The base is rounded. They are 20–49 × 27–66 µm (average 29.6 × 45 µm). The length–breadth ratio is 1.1:1–2.9:1. Sporangia are caducous with a medium pedicel length of less than 10 µm. Caducity is not always noted in the early reports.

 

Chlamydospores:

Chlamydospores are not produced.

 

Hyphae:

Hyphal swellings are small to large and resemble abortive reproductive organs.

 

Sexual Structures

 

P. heveae is homothallic.

 

Antheridia:

Antheridia are amphigynous and usually spherical but sometimes bicellular or cylindrical (10 × 11 µm).

 

Oogonia:

Smooth-walled oogonia form readily in culture in close groups or clusters and are globose. They are 17–32 µm in diameter (average 22.3 µm) and have a tapered or broadly funnel-shaped oogonial stalk. The oogonial wall is smooth.

 

Oospores:

Oospores are round, smooth, thick walled, 15–26.8 µm in diameter (average 21.5 µm), and markedly aplerotic (Figs. 3 and 4).

Host Range and Distribution

Host	Common Name	Disease	Geographical Distribution
Agathis australis	Kauri	Root rot	New Zealand, New Guinea
Bertholletia excelsa	Brazil nut	Leaf blight (Fig. 5)	Brazil
Cocos nucifera	Coconut	Bud rot; nut fall	Ivory Coast
Eucalyptus pilularis	Blackbutt	Trunk canker	Australia
Hevea brasiliensis	Para rubber tree	Black stripe	Malaysia
Mangifera indica	Mango	Leaf blight	India
Persea americana	Avocado	Trunk canker	Guatemala
Pinus patula	Mexican yellow pine	Root rot	Australia
Psidium guajava	Apple guava	Leaf blight	India
Rhododendron spp.	Rhododendron	Dieback; wilt	United States
Theobroma cacao	Cocoa	Pod rot	Malaysia

Symptoms

The pathogen has been reported on rubber, cacao, avocado, mango, guava, rhododendron, Brazil nut (Fig. 5), eucalyptus, and pine.

 

Black Stripe of Hevea:

The symptoms are similar to those caused by P. palmivora or P. meadii on Hevea spp. (Orellana, 1959). The pathogen causes a sunken discolored lesion on the bark above the tap area. Vertical fissures in the bark can occur, and when it is stripped away, a black line can be seen. Oospores form in the tissue in contrast to P. meadii and P palmivora. P. heveae causes watery green patches, covered with mycelium, on pods (Erwin and Ribeiro, 1996).

 

Pod Rot of Cacao:

The pathogen infects the pods and causes a light brown lesion. This lesion is lighter in color than the lesion caused by P. palmivora on cocoa pods. Oospores form abundantly, but few sporangia are produced (Waterhouse, 1974).

 

Trunk Canker of Avocado:

Cracked and bleeding cankers form on the lower levels of the trunk and on the upper rootstock of avocado trees. Diseased trees are stunted and the foliage turns light green. Dieback sometimes occurs when the pathogen spreads, and the trees eventually die.

References

Cline, E. T., Farr, D. F., and Rossman, A. Y. 2008. A synopsis of Phytophthora with accurate scientific names, host range, and geographic distribution. Plant Health Progress doi:10.1094/PHP-2008-0318-01-RS.

 

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

 

Orellana, R. G. 1959. Variation in Phytophthora palmivora isolated from cacao and rubber. Phytopathology 49:210-213.

 

Stamps, D. J. 1978. Phytophthora heveae. CMI Descr. Pathog. Fungi Bact. 594:1-2.

 

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.

 

Thompson, A. W. 1929. Phytophthora species in Malaysia. Malay. Agric. J. 17:53-100.

 

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.

 

Waterhouse, G. M. 1974. Other Phytophthora species recorded on cacao. Pages 71-79 in: Phytophthora Disease of Cacao. P. H. Gregory, ed. Longman, London.