Introduction
Phytophthora meadii
McRae (1918)
Phytophthora meadii
was first described by McRae (1918) from diseased rubber trees,
Hevea brasiliensis,
in
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 |
|
Ananas comosus |
Pineapple |
Top rot |
|
Areca catechu |
Areca nut |
Koleroga; fruit rot |
|
Clarkia elegans |
Elegant clarkia |
Seedling blight |
|
Dianthus caryophyllus |
Carnation, oeillet |
Wilt; stem rot |
|
Elettaria cardamomum |
Cardamom |
Blight |
|
Euonymus japonicus |
Spindle tree |
Blight |
|
Gilia
spp. |
Phlox |
Seedling blight |
|
Hevea brasiliensis |
Rubber |
Black thread; stripe canker; bark and pod rot; secondary leaf fall |
|
Manihot glaziovii |
Ceara rubber tree |
Leaf blight |
India |
Piper betle |
Betel |
Foot rot |
|
Ricinus communis |
Castor bean, castor oil plant |
Seedling blight |
|
Salpiglossis spp. |
Painted tongue |
Seedling blight |
|
Solanum melongena |
Eggplant, brinjal, aubergine |
Blight |
|
Theobroma cacao |
|
Black pod |
|
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 ,
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
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,
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,
Waterhouse, G. M. 1963. Key to the species of
Phytophthora de Bary. Mycol. Pap. 92.
CAB
International, Wallingford, United Kingdom; Commonwealth Mycological Institute,
Kew,
Waterhouse, G. M. 1974. Phytophthora
palmivora and some related species. Pages 51-70 in:
Phytophthora Disease of