Introduction
Phytophthora hibernalis Carne
(1925)
Phytophthora hibernalis
was first isolated from diseased citrus in
Cultural Characteristics
The minimum temperature for growth is less than 5°C, the optimum temperature for growth is 15°C, and the maximum temperature for growth is 25°C. The colony grows in a rosette pattern (Fig. 2).
Reproductive Structures
Asexual Structures
Sporangiophores:
Sporangiophores are unbranched or can form as long, lateral branches in an
irregular
sympodium.
Sporangia:
Sporangia are
semipapillate and caducous with a long
pedicel (23–73 µm) (Blomquist et al., 2005) (Fig. 3).
Sporangia are elongated, ellipsoid, ovoid, or obovoid and tapered at the base;
most of the time the broadest point is at the apex of the sporangia. Sporangia
are 14–22 × 29–53 µm (average 19 × 40 µm).
Chlamydospores
and Hyphal Swellings:
Chlamydospores and hyphal swellings are not formed.
Sexual Structures
P. hibernalis is
homothallic.
Antheridia:
Antheridia are mostly
amphigynous but occasionally
paragynous.
Oogonia:
Oogonia are 22–56 µm in diameter (average 35 µm) (Fig. 4).
Oospores:
Oospores are plerotic and 22–45.6 µm in diameter (average 30 µm).
Host Range and Distribution
Host |
Common Name |
Disease |
Geographical Distribution |
Agathis australis |
Kauri pine |
Canker |
New Zealand |
Carthamus tinctorius |
Safflower |
Root rot |
Venezuela |
Chamaecyparis lawsoniana |
Port-Orford white cedar |
Canker |
United Kingdom |
Citrus spp. |
Citrus |
Leaf blight; brown rot of fruit; defoliation; twig blight; fruit decay; twig dieback |
Australia; Portugal; Israel; Fiji Islands; Turkey; South Africa; United States; Italy; France |
Rhododendron spp. |
Rhododendron |
Leaf blight |
United States |
Lycopersicon esculentum |
Tomato |
Root rot |
Israel |
Malus pumila |
Apple |
Root rot |
Israel |
Sesamum indicum |
Sesame, gingelly |
Root rot; stem canker |
Venezuela |
Solanum melongena |
Eggplant, brinjal |
Root rot |
Israel |
Symptoms
Symptoms of brown rot on citrus caused by P. hibernalis are similar to those caused by P. citrophthora, P. nicotianae, and P. syringae. The pathogen infects citrus fruit on the bottom end from splash dispersal from the soil. Infected areas on the fruit coalesce. The diseased fruit is brown and leathery and can mummify on the tree and eventually drop to the ground. The pathogen can sporulate on the fruit surface. The pathogen infects during the cool season and disease is more severe with rain and wind (Erwin and Ribeiro, 1996). Caducous sporangia can infect the upper parts of the tree.
The pathogen has also been isolated from symptomatic rhododendrons and causes leaf lesions (Figs. 5 and 6). P. hibernalis could potentially be misdiagnosed by polymerase chain reaction (PCR) as P. ramorum (Blomquist et al., 2005) since internal transcribed spacer (ITS) DNA sequences are very similar.
Disease develops rapidly under conditions of high humidity and soil moisture.
The greatest damage occurs after rainfall and wind during autumn and winter.
References
Blomquist, C., Irving, T., Osterbauer, N., and Reeser, P. 2005. Phytophthora
hibernalis: A new pathogen on Rhododendron and evidence of cross
amplification with two PCR detection assays for Phytophthora ramorum. Plant Health Progress
doi:10.1094/PHP-2005-0728-01-HN.
Carne, W. M. 1925. A brown rot of citrus in
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,
Ho, H. H., and Jong, S. C. 1993.
Phytophthora hibernalis and Phytophthora syringae. Mycotaxon 47:439-460.
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,
Tucker, C. M.
1931. Taxonomy of the genus
Phytophthora de Bary. Univ.
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., and Waterston, J. M.
1964.
Phytophthora hibernalis. CMI Descr. Pathog. Fungi Bact.
31:1-2.