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Figure 1. Morphology of Phytophthora meadii. Upper row, Obpyriform to ellipsoid sporangia; sporangium with swollen sporangiophore; elongated, hourglass-shaped sporangia; sporangia produced on a simple sympodium (does not conform to size bars). Center row, Curved, papillate, caducous sporangium; sporangium sessile on the mycelium; sporangium with an elongated, ellipsoid, abnormal shape. Lower row, Amphigynous antheridia on globose to obpyriform oogonia (oospores are distinctly aplerotic); old hyphal section with a septum; mycelial pattern. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

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

Figure 3. Sporangia of Phytophthora meadii (×1,000). (Courtesy Jean B. Ristaino)

Figure 4. Oogonia of Phytophthora meadii with an amphigynous antheridium. (Courtesy Jean B. Ristaino)

Figure 5. Leaf spots, caused by Phytophthora meadii, on Leea coccinea (west Indian holly) begin as small, irregularly shaped, dark, water-soaked flecks. These expand to distinct dark spots. (Courtesy Janice Y. Uchida; Reproduced from Phytophthora meadii. Crop Knowledge Master. Extension Entomology and UH-CTAHR IPM Program, University of Hawaii-Manoa)

Figure 6. Drooping leaves or leaflets on red leea are a sign of Phytophthora meadii infection. (Courtesy Janice Y. Uchida; Reproduced from Phytophthora meadii. Crop Knowledge Master. Extension Entomology and UH-CTAHR IPM Program, University of Hawaii-Manoa)

Figure 7. On red leea cultivars infected with Phytophthora meadii, the leaf blight color sometimes closely matches leaf color and blights are difficult to detect. (Courtesy Janice Y. Uchida; Reproduced from Phytophthora meadii. Crop Knowledge Master. Extension Entomology and UH-CTAHR IPM Program, University of Hawaii-Manoa)

Introduction

Phytophthora meadii  McRae (1918)

 

Phytophthora meadii was first described by McRae (1918) from diseased rubber trees, Hevea brasiliensis, in India. P. meadii is responsible for stripe canker, black thread, pod rot, shoot dieback, and secondary leaf fall disease of rubber trees. The pathogen is also responsible for the koleroga or fruit rot disease of areca nut in Karnataka, India (Sastry and Hegde, 1987). While P. meadii was merged under the name P. palmivora with P. faberi in 1931, Waterhouse (1963; 1974) distinguished P. meadii from P. faberi. P. palmivora is a synonym of P. faberi. P. meadii is a group II Phytophthora species (Stamps et al., 1990) (Fig. 1).

Cultural Characteristics

The minimum temperature for growth is greater than 5°C, the maximum temperature for growth is greater than 33°C (Fig. 2). The optimum temperature for growth is 25–30°C. There is no colony growth at 35°C.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are slender and have nodal swellings from which branches arise (McRae, 1918). Sporangiophores are branched and 10–20 µm long on simple sympodium.

 

Sporangia:

Sporangia can be various shapes, ellipsoid, elongated ellipsoid ovoid, or obpyriform (McRae, 1918). They are terminal or lateral and papillate, occasionally with two papillae. They are caducous with a medium pedicel (10–20 µm long). On fruit, sporangia are 14–28 × 33–67 µm (average 21 × 48 µm) (Fig. 3). In water, sporangia are 16–29 × 20–44 µm (average 23 × 32 µm).

 

Chlamydospores:

Chlamydospores are rare. They are 16–30 µm in diameter, with the majority under 30 µm. Structures usually appear after 18 days of incubation at 30°C.

 

Hyphae:

Hyphae are variable and 2.5–6 µm in diameter. Hyphal swellings are not present in P. meadii.

 

Sexual Structures

 

P. meadii was described as mostly homothallic (Waterhouse, 1974), with some evidence of heterothallism (Peries and Dantanarayana, 1965). Gallegly and Hong (2008) describe the species as heterothallic. Sex organs are only developed at temperatures of 15–20°C.

 

Antheridia:

Antheridia are rounded, amphigynous, and 10–12 × 13–16 µm.

 

Oogonia:

Oogonia are spherical to pyriform and have smooth or wrinkled walls (Fig. 4). In agar, oogonia are 21–49 µm in diameter (average 33.4 µm), and on fruit, oogonia are 20–48 µm in diameter (average 25.1 µm).

 

Oospores:

Oospores are aplerotic and yellowish. On agar, media oospores are 16–32.8 µm in diameter (average 24 µm), and on fruit, oospores are 16–32 µm in diameter (average 21 µm). The oospore wall is 4 µm thick.

Host Range and Distribution

Host	Common Name	Disease	Geographical Distribution
Allium cepa	Onion	Root rot	United States
Ananas comosus	Pineapple	Top rot	United States
Areca catechu	Areca nut	Koleroga; fruit rot	India
Clarkia elegans	Elegant clarkia	Seedling blight	India
Dianthus caryophyllus	Carnation, oeillet	Wilt; stem rot	Mauritius
Elettaria cardamomum	Cardamom	Blight	India
Euonymus japonicus	Spindle tree	Blight	China
Gilia spp.	Phlox	Seedling blight	India
Hevea brasiliensis	Rubber	Black thread; stripe canker; bark and pod rot; secondary leaf fall	Indonesia, Sri Lanka, Burma, India, Nigeria, Congo, Thailand, Cambodia, Vietnam, Liberia, Ghana, Cameroon, Brazil, Peru, Nicaragua, Costa Rica, Venezuela
Manihot glaziovii	Ceara rubber tree	Leaf blight	India
Piper betle	Betel	Foot rot	Malaysia
Ricinus communis	Castor bean, castor oil plant	Seedling blight	India
Salpiglossis spp.	Painted tongue	Seedling blight	India
Solanum melongena	Eggplant, brinjal, aubergine	Blight	India
Theobroma cacao	Cocoa	Black pod	India

Symptoms

Stripe Canker, Black Thread, Secondary Leaf Fall, and Green Pod Decay of Hevea brasiliensis (Rubber):

Fruits of the plant develop dull, ash gray spots, starting at the stem end of the fruit and gradually spreading across the entire surface, eventually coalescing. The spots appear approximately 3 weeks into the monsoon season, and if the weather is humid, a whitish fuzz of mycelium and sporangia can cover the infected portions. The spots can also start exuding drops of latex and the fruits turn dark and soft. Leaves can also be infected, turning colors and shedding. Once the leaves fall, branches die back and the shoots that arise from these branches during the following season wilt early (Pillai, 1982). P. botryosa is closely related to P. meadii and is also responsible for the disease of rubber.

 

Top Rot of Anana comosus (Pineapple):

Symptoms of top rot are visible as brown spots on green fruit that gradually extend to cover the whole fruit. Diseased fruits have a dry and lighter-colored pulp than do healthy fruits, and the pulp is surrounded by a brown or discolored margin. The leaf bases and the stem may also become infected. Heart rot, caused by P. cinnamomi, may be the most well-recognized disease among pineapple plants.

 

Leaf Blight of Red Leea:

P. meadii can cause leaf spots on Leea spp. Symptoms begin as small, irregularly shaped, dark, water-soaked flecks. These expand to distinct dark spots. Drooping and dead leaves are a sign of infection (Figs. 5–7).

References

Gallegly, M., and Hong, C. 2008. Phytophthora: Identifying Species by Morphology and DNA Fingerprints. American Phytopathological Society , St. Paul, MN.

 

McRae, W. 1918. Phytophthora meadii n. sp. on Hevea brasiliensis. Mem. Dep. Agric. India Bot. Ser. 9:219-273.

 

Peries, O. S., and Dantanarayana, D. M. 1965. Compatibility and variation in Phytophthora cultures isolated from Hevea brasiliensis in Ceylon. Trans. Br. Mycol. Soc. 48:631-637.

 

Pillai, P. N. R. 1982. Abnormal leaf fall of rubber caused by Phytophthora spp. Pages 17-23 in: Proc. Workshop on Phytophthora Diseases of Cultivated Plants. K. K. N. Nambiar, ed. Central Plantation Crops Research Institute, Kasaragod, Kerala, India.

 

Sastry, M. N. L., and Hegde, R. K. 1987. Phytophthora associated with arecanut (Areca catechu Linn.) in Uttara Kannada, Karnataka. Curr. Sci. 56:367-368.

 

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.

 

Waterhouse, G. M. 1974. Phytophthora palmivora and some related species. Pages 51-70 in: Phytophthora Disease of Cocoa. P. H. Gregory, ed. Longman, London.