Introduction
Phytophthora lateralis
Tucker & Milbrath (1942)
Phytophthora lateralis
was first described by Tucker and Milbrath (1942) from diseased Lawson cypress
in the northwestern
Cultural Characteristics
P. lateralis is slow growing. The minimum temperature for growth is 3°C, and the maximum temperature for growth is less than 26°C (Fig. 2). The optimum temperature for growth is 20°C.
Reproductive Structures
Asexual Structures
Sporangiophores:
A description of morphology can be found in Hall (1991). Sporangiophores are compound and can grow below the base of a sporangium or through the base of an empty sporangium.
Sporangia:
Sporangia are nonpapillate, noncaducous, and borne sympodially on simple sporangiophores. They are ovate, obovate, obpyriform, and often elongated or distorted in shape. Sporangia are 12–20 × 20–60 µm (average 15 × 26 µm) (Fig. 3). The length–breadth ratio is 1.6:1–1.9:1. Sporangia form most readily in weak agar media (V-8 juice, 10 ml/liter; whole milk, 20 ml/liter; and cornmeal, 25 g/liter) and in continuous incubation under a combination of blacklight blue and cool white fluorescent lamps.
Chlamydospores:
Chlamydospores are abundant, characteristically lateral, sessile on the hyphae, and cinnamon brown . This is a characteristic morphological trait from which the pathogen received its name (Tucker and Milbrath, 1942). Chlamydospores are most often found in agar media at temperatures of 15–25°C. They are 20–77 µm in diameter (average 40 µm). The production of chlamydospores is inhibited by light (Fig. 1).
Hyphae:
Hyphae grow best at 15°C and are up to 8 µm wide. Hyphae branch irregularly and can become septate as cultures age. P. lateralis does not produce hyphal swellings (Erwin and Ribeiro, 1996).
Sexual Structures
P. lateralis is homothallic.
Antheridia:
Antheridia are paragynous. They occur singly and are (sub)globulose, colorless, and delimited from hyphae by septa (Hall, 1991).
Oogonia:
Oogonia are produced in single culture. They are smooth, spherical, thin walled, and terminal and are 33–50 µm in diameter but absent in most isolates.
Oospores:
Oospores are
plerotic and made up of 6-µm-thick walls.
They are deeply pigmented (color depending on the agar medium used) and grow best on
agar of Port-Orford cedar foliage (Trione, 1974).
Oospores are 28–46 µm in diameter (average 40 µm).
Host Range and Distribution
Host |
Common Name |
Disease |
Geographical Distribution |
Chamaecyparis lawsoniana, C. lawsoniana
var. elwoodi, var.
cerula, |
Port-Orford cedar, cypress |
Root and crown rot |
North America |
Chamaecyparis obtusa
var. crippsii |
Golden hinoki cypress |
Root and crown rot |
North America |
Taxus brevifolia |
Pacific yew |
Root and crown rot |
North America |
Rhododendron
spp |
Rhododendron |
Root and crown rot |
North America |
Thuja orientalis |
White cedar |
Root and crown rot |
North America |
Hosts are found in North America and include the species listed above (DeNitto and Kliejunas, 1991; Erwin and Ribeiro, 1996; Roth et al., 1972).
P. lateralis causes root and crown rot in host species.
Symptoms
Root Rot of
Chamaecyparis lawsoniana:
The pathogen is an important host of the timber tree Port-Orford cedar. The first symptom of disease is a light foliage color. Foliage wilts on warm days and gradually changes color from yellow to bronze to light brown or tan. In the end, the foliage becomes crisp and dry. The infection of roots and the spreading of the infection up the tree lead to the color changes in foliage (Figs. 4 and 5). Infected roots appear water-soaked and have a deep cinnamon brown color. When the bark is removed, a clear zone of differentiation is visible between infected and healthy tissues. A black resinous line can be seen in the cambium. Young trees can be killed within weeks and older ones decline over the years (Fig. 6). The disease is more severe under cool wet conditions and rainfall (Zobel et al., 1985).
References
Atkinson, R. G. 1965. Phytophthora
species inciting root rot of
Chamaecyparis lawsoniana and other ornamentals in coastal
DeNitto, G. A., and Kliejunas, J. T. 1991. First report of
Phytophthora lateralis on Pacific yew. Plant Dis. 75:968.
Erwin, D. C., and Ribeiro, O. K. 1996.
Phytophthora
Diseases Worldwide. American
Phytopathological Society,
Hall, G. F. 1991. Phytophthora lateralis.
Mycopathologia 115:227-229.
Roth, L. F., Bynum, H. H., and Nelson, E. E. 1972. Phytophthora root rot of
Port-Orford cedar.
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,
Trione, E. J. 1974. Sporulation and germination of
Phytophthora lateralis. Phytopathology 64:1531-1533.
Tucker, C. M., and Milbrath, J. A.
1942. Root rot of
Chamaecyparis caused by a species of
Phytophthora. Mycologia 34:94-103.
Waterhouse, G. M. 1963. Key to the species of
Phytophthora de Bary. Mycol. Pap. 92.
CAB International, Wallingford, United Kingdom; Commonwealth Mycological
Institute, Kew,
Zobel, D. B., Roth, L. F., and Hawk, G. M. 1985. Ecology, pathology, and management of Port-Orford-cedar (Chamaecyparis lawsoniana). Gen. Tech. Rep. PNW-184. U.S. Dep. Agric. For. Ser. Pac. Northwest For. Range Exp. Stn., Portland, OR.