Introduction
Phytophthora citricola Sawada (1927)
Phytophthora citricola
was first isolated from Sekkan orange fruit with brown rot
symptoms in
Cultural Characteristics
Cultural characteristics include a stellate or rosette pattern on agar medium (Fig. 2). The minimum temperature for growth is 3°C, the optimum temperature for growth is 25–28°C, and the maximum temperature for growth is 31°C.
Reproductive Structures
Asexual
Structures
Sporangiophores:
Sporangiophores are long and slender, up to 3 µm wide and often swelling,
particularly at the point of branching. Branching is irregular and lax, not
regularly sympodial, and not often occurring immediately beneath the
sporangium (Waterhouse and Waterston, 1966).
Sporangia:
Sporangia are absent or rare on solid media but readily form in water solution. The shape of the sporangia is highly variable, ranging from obovoid, obclavate, and obpyriform to slightly flattened on one side to irregularly shaped with three to four lobes (Bush et al., 2006) (Fig. 3). Sporangia are semipapillate, and the papillae are wide and flat. Sporangia are 21–44 × 30–75 µm (average 34 × 47 µm). The length–breadth ratio is less than 1.6. They are noncaducous and persistent on the stalk. The cross wall at the base of the sporangium is flush with the base without a septal plug. Gallegly and Hong recognize three forms (I, II, and III), based on DNA markers, sporangia, and antheridial characters, including type I, sporangia with multiple apices, large inflated antheridia (>13 µm), distortion, and lateral attachments; type II, ovoid sporangia and small antheridia (<10 µm); and type III, ellipsoid sporangia with antheridia perpendicular to the oogonium (Gallegly and Hong, 2008).
Chlamydospores:
Chlamydospores are rare and reported on oatmeal agar only in some isolates.
Hyphae:
Hyphae are 6 µm wide and without frequent hyphal
swellings.
Sexual Structures
P. citricola is
homothallic and sex organs are abundant on most media.
Antheridia:
Antheridia are
paragynous (rarely
amphigynous) and often
diclinous. The antheridium cell is small, 1–12 × 7.5 µm, and
can be inflated or perpendicular to the oogonium.
Oogonia:
Oogonia are spherical and 18–35 µm in diameter (average 25.5 µm), sometimes
tapering to a funnel-shaped base. The wall is smooth, thin, and pale yellow to
yellowish brown.
Oospores:
Oospores are spherical, almost
plerotic, and 16–30 µm (average 22.0 µm) (Fig. 4).
Host Range and Distribution
Host |
Common Name |
Disease |
Geographical Distribution |
Abies spp. |
Balsam fir, white fir, Fraser fir |
Crown rot; blight; canker |
Unites States |
Acer saccharum |
Sugar maple |
Collar rot |
|
Actinidia chinensis |
Kiwifruit |
Collar and root rot |
|
Aesculus hippocastanum |
Horse chestnut |
Bleeding canker; root rot; dieback |
|
Antirrhinum spp. |
Snapdragon |
Root rot |
|
Aucuba japonica |
Gold dust plant |
Root rot |
|
Azalea indica |
Formosa azalea |
Root rot |
|
Beaufortia sparsa |
Swamp bottlebrush |
Root rot |
|
Brachychiton populneus |
Bottle tree |
Root rot |
|
Ceanothus griseus |
Ceanothus |
Trunk canker |
|
Chamaecyparis lawsoniana |
Lawson cypress; Port Orford cedar |
Wilt |
|
Chamelaucium uncinatum |
Geraldton wax |
Root rot |
|
Citrus spp. |
Citrus |
Shoot blight; fruit rot; brown fruit rot |
Australia, Antilles, Japan, Portugal, South Africa, Taiwan, United Kingdom |
Corylus avellana |
European hazel |
Collar and trunk canker |
|
Cyclamen
spp. |
Persian violet |
Leaf blight |
|
Cydonia oblonga |
Quince |
Root rot |
|
Cytisus praecox |
Legume |
Root rot |
|
Erica hiemalis |
White heather |
Decline |
|
Euphorbia resinifera |
Spurge |
Root rot |
|
Feijoa sellowiana |
Feijoa |
Brown rot of fruit |
|
Fragaria chiloensis |
Strawberry |
Fruit rot |
|
Hakea francisiana |
Red spike hakea |
Root rot |
|
Hebe pinguifolia |
Pagei Hebe |
Root and stem rot |
|
Hevea brasiliensis |
Rubber |
Root and stem rot |
|
Hibiscus rosa-sinensis |
China rose |
Root rot; wilt |
|
Hibiscus schizopetalus |
Japanese lantern |
Root rot; wilt; black root |
|
Humulus lupulus |
Hop |
Collar and trunk canker; crown and root rot |
|
Juglans
spp. |
Black and English walnut |
Root and crown rot |
|
Lycopersicon esculentum |
Tomato |
Basal rot; seedling wilt |
|
Malus pumila |
Apple |
Root rot |
|
Olea europaea |
Olive |
Collar and trunk canker |
|
Persea |
Avocado |
Trunk canker; fruit rot |
|
Phaseolus vulgaris |
Kidney bean |
Root rot |
|
Pieris japonica |
Japanese andromeda |
Shoot blight; stem dieback |
|
Pinus radiata |
|
Root rot |
|
Pistacia vera |
Pistachio |
Apoplexy; wilt |
|
Platanus orientalis |
Oriental plane tree |
Collar and trunk rot |
|
Primula japonica |
Primrose |
Root rot |
|
Prunus spp. |
Almond, apricot, cherry, peach |
Collar rot; root and crown rot |
|
Pseudotsuga menziesii |
Douglas fir |
Crown rot |
|
Psidium guajava |
Guava |
Fruit rot |
|
Quercus spp. |
|
Trunk canker; seedling root rot |
|
Rhododendron spp. |
Rhododendron |
Bud, leaf, and twig blight; wilt |
|
Rubus idaeus |
Raspberry |
Root rot |
|
Sambucus spp. |
Elder |
Crown rot |
|
Schinus molle |
Australian or |
Crown rot |
|
Syringa vulgaris |
Lilac |
Shoot blight of suckers |
|
Tilia spp. |
Lime |
Bark canker |
|
Vitis vinifera |
Grape |
Root rot |
|
Symptoms
Bleeding
Canker of Horse Chestnut:
Dead and dying scaffold branches normally show the first signs of infection. A
rusty red or yellow-brown fluid oozes out of recently killed bark. This fluid
eventually turns black and crusty.
Root Rot,
Leaf Spots, Shoot Blight, and Stem Dieback of Ericaceous Woody Ornamentals:
Blight occurs in young tissue (terminal growth).
Mature wood is rarely affected. Spots on leafs are surrounded by a dark red
margin, eventually causing leaves to fall off. Root and crown rot causes
chlorosis, wilting, decreased foliage, and stunting of the plant. In advanced
stages of the disease, dieback occurs.
Stem necrosis from splash dispersal of soilborne inoculum can occur.
P. citrophthora is more important than
P. citricola on Pieris
spp.
P. citricola causes a stem dieback on
Rhododendron spp.
Root Rot of
Walnut:
In
Crown and
Collar Rot of Avocado:
Disease begins as a canker at the base of the trunk (Figs. 5 and 6). This canker moves so slowly that it can go unnoticed until girdling has occurred and foliage begins to yellow (Zentmyer and Ohr, 1978). The development of cankers is favored by high soil moisture levels. Root rot caused by P. cinnamomi is more common on avocado. Infection of avocado by P. citricola may be predisposed by root pruning and wounding. Susceptibility of wounded trees to disease is seasonally affected and timed with flushes of tree growth.
References
Bush, E. A., Stromberg, E. L., Hong, C., Richardson, P. A., and Kong, P. 2006.
Illustration of key morphological characteristics of Phytophthora species
identified 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.
Cooke, D. E. L., Drenth, A.,
Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora
Diseases Worldwide. American Phytopathological Society,
Ho, H. H., and Chang, H. S.
1992. A re-evaluation of
Phytophthora
species described by K. Sawada in
Gallegly, M. E., and Hong, C. 2008. Phytophthora: Identifying Species by Morphology
and
DNA Fingerprints. American Phytopathological Society,
Kroon, L. P. N. M., Bakker, F. T., van den Bosch, G. B. M., Bonants, P. J. M.,
and Flier, W. G.
2004.
Phylogenetic analysis of
Phytophthora species based on mitochondrial and nuclear DNS
sequences. Fungal Genet. Biol. 41:766-782.
Leonian, L. H. 1925.
Physiological studies on the genus
Phytophthora.
Leonian, L. H. 1934.
Identification of
Phytophthora species. W.
Mircetich, S. M., and Matheron, M. E. 1983. Phytophthora root and crown rot of
walnut trees. Phytopathology 73:1481-1488.
Sawada, K. 1927. Descriptive catalogue of the Formosan fungi III. Dep. Agric.
Gov. Res. Inst.
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,
Sundararaman, S., and Ramakrishnan, T. S. 1928. Foot rot and wilt of Antirrhinums.
Mem. Dep. Agric. India Bot. Ser. 16:83-100.
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. 1966.
Phytophthora citricola.
CMI Descr. Pathog. Fungi Bact. 114:1-2.
Zentmyer, G. A., and Ohr, H. D. 1978. Avocado root rot.
Div. Agric. Serv.