Introduction
Phytophthora ilicis Buddenh. & Roy A. Young (1957)
Phytophthora ilicis
was first described by Buddenhagen and Young in 1957 on English holly in the
western
Cultural Characteristics
The minimum temperature for growth is 5°C, the optimum temperature for growth is 20°C, and the maximum temperature for growth is 25°C (Fig. 2).
Reproductive Structures
Asexual Structures
Sporangiophores:
Sporangiophores are sympodial and form in water.
Sporangia:
Sporangia are obpyriform, ovoid to spherical, semipapillate, and caducous with a medium pedicel length of 5–15 µm. Sporangia are small, 18–30 × 30–50 µm (average 24 × 39 µm on holly tissue). Sporangial length–breadth ratios are 1.3:1–1.6:1 (Fig. 1).
Chlamydospores and Hyphal Swellings:
Chlamydospores are rare and hyphal swellings are not produced.
Sexual Structures
P. ilicis is homothallic.
Antheridia:
Antheridia are amphigynous.
Oogonia:
Oogonia have a tapered base and are small, 25–32 µm in diameter (average 27 μm) in leaves and 17–28 µm in diameter (average 25 µm) in pea broth.
Oospores:
Oospores are plerotic and 18–26 µm in diameter (average 21 µm) in leaves and
15–23 µm (average 20 µm ) in pea broth (Fig. 3).
Host Range and Distribution
Host |
Common Name |
Disease |
Geographical Distribution |
Ilex aquifolium |
English holly |
Leaf and twig blight |
|
Ilex crenata |
Japanese holly |
Leaf and twig blight |
|
Symptoms
The appearance of black spots on the periphery leaves of the lower part of the holly
tree is the first observable symptom (Fig. 4). This happens during cool, wet
weather in the fall. Defoliation occurs after the leaf spots. Cankers can occur on
the twigs and stems and do not exceed 12 cm in length (Erwin and Ribeiro, 1996).
Berries are also susceptible to infection and the twig beneath the berry can
become girdled (Fig. 5). The disease can
progress up the tree and eventually defoliate the entire tree.
The pathogen sporulates on the underside of the leaf surfaces and
oospores form in the tissue.
References
Buddenhagen,
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,
Hall, G. 1991. Phytophthora ilicis. Mycopathologia 115:225-226.
Pscheidt, J. W., ed. 2010. Holly—Phytophthora Leaf and Twig Blight. Online Guide to Plant Disease Control. Oregon State University Extension, Corvallis, OR.
Punja, Z. K., and Omrod, D. J. 1979. New or noteworthy plant diseases in coastal
British Columbia 1975-1977.
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. 1970. Taxonomy in
Phytophthora . Phytopathology 60:1141-1143.
Waterhouse, G. M., and Waterston, J. M.
1964. Phytophthora hibernalis. CMI Descr. Pathog. Fungi Bact.
31:1-2.