Figure 1. Morphology of Phytophthora drechsleri. Upper row, Nonpapillate, ellipsoid to obpyriform sporangia; internal proliferation. Lower row, Globose oogonia with amphigynous antheridia; sporangia forming in a sympodium; hyphal swellings formed in aqueous culture. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

 

Figure 2. Culture of Phytophthora drechsleri grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

 

Figure 3. Nonpapillate sporangium of Phytophthora drechsleri. Bar = 10 µm. (Courtesy Elizabeth A. Bush; Reproduced from Bush et al., 2006)

 

Figure 4. Hyphal swellings of Phytophthora drechsleri (×400). (Courtesy Jean B. Ristaino)

 

Figure 5. Oogonium with an amphigynous antheridium and plerotic oospore of Phytophthora dreschleri. (Courtesy Jean B. Ristaino)

 

Figure 6. Stem rot, caused by Phytophthora drechsleri, on Euphorbia pulcherrima (poinsettia). (Courtesy Margery Daughtrey, Cornell University, Ithaca, NY)

 

Figure 7. Wilting of Calibrachoa (trailing petunia) plants from root rot caused by Phytophthora drechsleri. (Courtesy Margery Daughtrey, Cornell University, Ithaca, NY)

 

Figure 8. Dieback of Calibrachoa (trailing petunia) plant from root rot caused by Phytophthora drechsleri. (Courtesy Margery Daughtrey, Cornell University, Ithaca, NY)

 

Figure 9. Root rot of sugar beet caused by Phytophthora drechsleri. (Courtesy D. Kontaxis; Reproduced from APS Digital Image Collections, Diseases of Root and Tuber Crops, American Phytopathological Society, St. Paul, MN)

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Introduction

Phytophthora drechsleri  Tucker (1931)

 

Phytophthora drechsleri was originally isolated from rotting potatoes by Drechsler (1929) and described by Tucker (1931). Synonyms include P. erythroseptica var. drechsleri (Tucker) Sarej. (1936) (Erwin and Ribeiro, 1996; Waterhouse, 1970). Ho and Jong (1986) listed various synonyms as part of their broad species concept. They considered P. cryptogea to be synonymous with P. drechsleri (Cline et al., 2008). Cooke et al. (2000) found the two species to be distinct based on molecular analysis. P. melonis and P. sinensis were also found to be distinct from P. drechsleri. Cooke et al. (2000) also found that P. drechsleri is not closely related to P. cajani, which should be considered a distinct species and not a forma specialis or variety of P. drechsleri. P. drechsleri is a group VI species (Stamps et al., 1990) (Fig. 1).

Cultural Characteristics

Colonies form in cottony patterns, but this is not consistent for all colonies (Fig. 2). The colony has profuse aerial mycelium and is slightly rosette. The minimum temperature for growth is 5°C, and the optimum temperature for growth is 28–31°C. P. drechsleri can grow at temperatures above 35°C. This feature distinguishes P. drechsleri from P. cryptogea.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are usually narrow. Sympodia form in water. Sporangiophores tend to widen slightly below the sporangium and are usually unbranched, with a single terminal sporangia. Growth is by internal proliferation of sporangia beyond the first one.

 

Sporangia:

Sporangia vary in shape from broadly obpyriform to ovoid. Sporangia are nonpapillate and noncaducous and persistent on the stalk. They average 26–40 × 36–70 µm (Bush et al., 2006) (Fig. 3).

 

Chlamydospores:

Chlamydospores only grow on some isolates and are 4.2–11.0 µm in diameter (average 7.9 µm).

 

Hyphae:

Hyphal swellings are round or angular and form in chains or netlike clusters (Fig. 4).

 

Sexual Structures

 

P. drechsleri is usually heterothallic. However, oospores have been reported forming in single cultures. When A1 and A2 mating types are paired, oospores are readily produced.

 

Antheridia:

Antheridia are amphigynous, oval or cylindrical, and 13 × 14–15 µm.

 

Oogonia:

Oogonia are tapered at the base and 22–53 µm in diameter (average 33 µm) (Fig. 5).

 

Oospores:

Oospores nearly fill the oogonium and are plerotic, measuring 17–50 µm in diameter (average 26 µm).

 

Features distinguishing P. drechsleri from P. cryptogea include higher minimum, optimum, and maximum temperatures for growth; larger and often distinctly shaped sporangia; and larger oogonia for P. drechsleri (Stamps, 1984). 

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Actinidia deliciosa

Kiwifruit

Root rot

Unites States

Adenanthos sericeus

Coastal woollybush

Root rot

Australia

Albizia stipulata

Tamalini

Bark canker; dieback

Malagasy Republic

Asimina triloba

Pawpaw

Fruit, trunk, collar, and root rot

Sarawak

Atylosia spp.

Pigeon pea

Stem rot

India

Azalea indica

Azalea

Root rot

Australia

Banksia spp.

Banksia

Root rot

Australia

Beta vulgaris

Sugar beet

Wet rot; taproot rot

United States, Iran

Boronia megastigma

Brown boronia

Root rot

Australia

Brassica spp.

Cabbage, turnip

Root rot

South Africa, United States

Cajanus cajan

Pigeon pea

Stem rot

India

Calibrachoa spp.

Trailing petunia

Root rot

United States

Callistemon spp.

Bottlebrush

Root rot

Australia

Callitris preissii

Cypress pine

Root rot

Australia

Calluna vulgaris

Heather

Root rot

Australia

Calytrix angulata

Yellow starflower

Root rot

Australia

Capsicum annuum

Chili pepper

Fruit rot

United States

Carthamus spp.

Saffron thistle, safflower, false saffron

Root rot; preemergence damping-off

United States, Iran, Australia

Cedrus deodara

Deodar

Root and crown rot; chlorosis

United States, China

Celosia plumosa

Woolflower

Root rot; stem necrosis

Argentina

Chamelaucium spp.

Geraldton wax plant, waxflower

Root rot

Australia

Chondrilla juncea

Skeleton weed

Necrosis; wilt

Australia

Chrysanthemum cinerariifolium

Pyrethrum

Root rot

Argentina

Cicer arietinum

Chickpea, garbanzo bean

Root rot

Iran

Citrullus spp.

Camel melon, watermelon

Necrosis; wilt; stem, leaf, root, and seed blight; fruit rot

Australia, Japan

Coleonema pulchrum

Pink breath of heaven

Root rot

Australia

Coleus spp.

Flame nettle, painted nettle

Root rot

Argentina

Coprosma repens

Mirror plant

Root rot

Australia

Cordyline australis

Dracena

Root rot

Australia

Crowea saligna

Willow-leaved crowea

Root rot

Australia

Cucumis spp.

Honeydew melon, cucumber

Fruit rot; stem rot; green death; root and foot rot

United States, Iran, Japan, Egypt, Greece, China

Cucurbita spp.

Vegetable marrow, pumpkin

Fruit rot

Egypt

Daucus carota

Carrot

Root rot

United States, Japan

Dodonaea spp.

Hopseed bush, hop bush, akeake

Root rot

Australia

Eutaxia obovata

Egg and bacon shrub

Root rot

Australia

Euphorbia pulcherrima

Poinsettia

Stem rot; foliage blight

United States

Gerbera jamesonii

Transvaal daisy, Barberton daisy

Root rot

United States

Grevillea spp.

Spider flower

Root rot

Australia

Hakea spp.

Pincushion tree

Root rot

Australia

Hebe spp.

Hebe

Root rot

Australia

Helianthus annuus

Sunflower

Stem rot

Iran

Indigofera australis

Indigo

Root rot

Australia

Isopogon cuneatus

Coneflower

Root rot

Australia

Kunzea spp.

Myrtle

Root rot

Australia

Lagerstroemia indica

Crape myrtle

Root rot

Australia

Lycopersicon esculentum

Tomato

Green fruit rot

United States, Argentina

Malus pumila

Apple

Root rot; trunk canker

United States

Manihot esculenta

Cassava, manioc

Soft rot; root rot

Brazil, Colombia

Medicago sativa

Alfalfa, lucerne

Root rot

Australia, South Africa

Melaleuca spp.

Honey myrtle, bottlebrush

Root rot

Australia

Mucuna deeringiana

Velvet bean

Root and stem rot; blight

Australia, Rhodesia

Parthenium argentatum

Guayule

Root and crown rot

United States

Pastinaca sativa

Parsnip

Root rot

United States

Pelargonium zonale

Geranium

Root rot

Argentina

Phaseolus vulgaris

Bean

Seedling blight

Japan

Pimelea ferruginea

Pink rice flower

Root rot

Australia

Pinus spp.

Pine

Pre- and postemergence damping-off; dieback

Australia

Prunus spp.

Almond, apricot, cherry, European plum, peach

Collar rot; root rot; trunk canker

Australia, Greece, United States

Pseudotsuga menziesii

Douglas fir

Root rot

United States

Schinus molle

Pepper tree, pirul, mastic tree

Bud and flower necrosis

Argentina

Senecio cruentus

Cineraria, groundsel

Collar and root rot

Argentina

Sesamum indicum

Sesame

Root rot

Rhodesia

Solanum spp.

Eggplant, potato

Seedling blight; tuber rot

United States

Viburnum tinus

Viburnum

Root rot

Australia

Washingtonia robusta

Thread palm

Collar rot

United States

Westringia rosmariniformis

Coast rosemary

Root rot

Australia

Xanthium spinosum

Bathurst burr

Leaf necrosis

Australia

Symptoms

Root and Stem Rot:

Stem rot affects safflower (Carthamus tinctorius), sunflower (Helianthus annuus), and poinsettia (Euphorbia pulcherrima) (Fig. 6). Root rot affects safflower, trailing petunia (Calibrachoa spp.) (Figs. 7 and 8), and sugar beet (Beta vulgaris) (Fig. 9), and a root and fruit rot can affect cucurbits (Erwin and Ribeiro, 1996). Plants at all stages of growth are susceptible to infection from P. drechsleri. In younger plants, symptoms resemble those of damping-off. Stem rot is observable, and the lower stem shrivels, causing the plant to eventually fall over and wilt. In older plants, black necrotic lesions form on the roots. This lesion formation eventually encompasses the roots and lower stem, causing the plant to fall over and wilt.

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 Virginia nursery irrigation water. Plant Health Progress doi:10.1094/PHP-2006-0621-01-RS.

 

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., Duncan, J. M., Wagels, G., and Brasier, C. M. 2000. A molecular phylogeny of Phytophthora and related oomycetes. Fungal Genet. Biol. 30:17-32.

 

Drechsler, C. 1929. A diplanetic species of Phytophthora causing pink rot of potato tubers. (Abstr.) Phytopathology 19:92.

 

Erwin, D. C., and Ribeiro, O.K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

 

Ho, H. H., and Jong, S. C. 1986. A comparison between Phytophthora cryptogea and P. drechsleri. Mycotaxon 27:289-319.

 

Sarejanni, J. A. 1936. A collar rot of cultivated Solanum and the classification of the genus Phytophthora. Ann. Inst. Phytopathol. Benaki 2:35-52.

 

Stamps, D. J. 1984. Phytophthora drechsleri. CMI Descr. Pathog. Fungi Bact. 840:1-2.

 

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, Surrey, England.

 

Tucker, C. M. 1931. The taxonomy of the genus Phytophthora de Bary. Univ. Mo. Agric. Exp. Stn. Res. Bull. 153.

 

Waterhouse, G. M. 1970. The genus Phytophthora. Diagnoses (or descriptions) and figures from the original papers. Mycol. Pap. 122. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.