Phytophthora niederhauserii Abad & J. Abad, 2014

California Pest Rating for
Phytophthora niederhauserii Abad & J. Abad, 2014
Pest Rating: B


Initiating Event:  

None.  A permanent rating for Phytophthora niederhauserii is proposed herein.

History & Status:

Background: In 2003, Abad and Abad reported the discovery of a Phytophthora species associated with necrotic collars, stems and roots of arborvitae (Thuja occidentalis L.) and English ivy (Hedera helix L.) grown in greenhouses in North Carolina.  They named the species, P. niederhauseria and submitted the ITS (Internal transcribed spacer) genetic sequences on GenBank-NCBI before publishing an official description of the species.  Soon other researchers from around the globe found that they were working with the same species based on the similarity of their test ITS sequences with that of P. niederhauseria in GenBank.  The species was discovered in 13 countries and associated with ornamentals, fruit trees and native plants.  However, it was only recently, that an official description of the species was published and the name, P. niederhauserii was validated (Abad et al., 2014).

Hosts: Abad et al., (2014) isolated P. niederhauserii from 33 plant hosts in 25 families from various countries.  A number of shrubs and herbaceous ornamental plants are hosts of the pathogen.  Few agricultural crops are also included.  Thuja occidentals (arborvitae), Hedera helix (English ivy), Abies nordmanniana, Acacia dealbata (Mimosa), Banksia baxteri, Banksia prionotes (acorn banksia), Banksia speciosa, various Begonia hybrids,  Callistemon citrinus, Ceanothus sp., Chamaecyparis lawsoniana, Cistus monspeliensis, C. salviifolius (sageleaf rockrose),  Grevillea olivacea, Heuchera sp. Iris sp. Juniperus sp., Kalanchoe blossfeldiana (kalanchoe), Manihot esculenta, Metrosideros villosa, Peperomia clusiifolia,Pistacia lentiscus, Plumbago sp., Prunus dulcis (almond), Punica granatum, Rhododendron catawbiense (catawba rhododendron), Sinningia speciosa (gloxinia), Spathiphyllum sp., Vitis vinifera (grape), and Xanthorrhoea australis (Farr & Rossman, 2014; Abad et al., 2014).

Symptoms:  Generally, Phytophthora niederhauserii infestations cause symptoms of root and stem collar necrosis resulting in wilting and leaf desiccation or drop in host plants.  In Norway, symptoms of P. niederhauserii infestation on greenhouse-potted begonia, gloxinia and ivy included necrotic roots and stems with necrosis extending to the leaves via the petioles.  Wilting of the entire plant was observed in gloxinia and ivy. In kalanchoe, only root discoloration and stunted plant growth are apparent (Herrero et al., 2008).  In Spain, symptoms on almonds included leaf chlorosis and drop, wilting, cankers and gum exudation.  In spring, symptoms included failure to leaf-out, death of scion and rootstock sprouts (Pérez-Sierra et al., 2010). The pathogen caused collar and root necrosis in boxwood associated with severe wilting and desiccation of foliage (Józsa et al., 2010).

Damage Potential: Quantitative economic losses in plant production due to Phytophthora niederhauserii have not been reported, however, infestations may result in significant damage and loss in production and stands of host plants by causing root and crown/basal stem rots of infected plants. Nursery ornamentals and plants grown in natural ecosystems are particularly affected. Infections may lead to death of the plant.  Generally, annual plants and young seedlings of trees may be killed by the disease within a few days, weeks or months (Agrios, 2005). The pathogen can potentially cause crown rot in grapes – as detected in South Africa and in almonds in Turkey (Abad et al., 2014).       

Disease Cycle: Generally, species of Phytophthora that cause root and stem rots survive cold winters or hot and dry summers as thick-walled, resting spores (oospores and chlamydospores) or mycelium in infected roots, stems or soil.  During spring, the oospores and chlamydospores germinate to produce motile spores (zoospores) that swim around in soil water and roots of susceptible hosts. The pathogen infects the host at the soil line causing water soaking and darkening of the trunk bark. This infected area enlarges and may encircle the entire stem of small plants which wilt and eventually die.  On large plants and trees, the infected, necrotic area may be on one side of the stem and become a depressed canker below the level of the healthy bark.  Collar rot canker may spread down the root system. Roots are invaded at the crown area or at ground level.   Mycelium and zoospores grow in abundance in cool, wet weather causing damage where the soil is too wet for normal growth of susceptible plants and low temperatures (15-23°C) prevail (Agrios, 2005).

Transmission:  Infected soils, plants, nursery and planting stock, seedlings, run-off and splash irrigation water, cultivation equipment and tools that may spread contaminated soil and plant materials to non-infected sites.

Worldwide Distribution:  Widespread.  Thirteen countries, namely, Australia, Hungary, Israel, Italy, Japan, the Netherlands, Norway, South Africa, Spain, Taiwan, Turkey, the United Kingdom and the USA (Abad et al., 2014).

In the USA, Phytophthora niederhauserii has been found in California, North Carolina, South Carolina (Robayo-Camacho et al., 2009; Farr & Rossman, 2014).

Official Control:  None reported.

California Distribution: Phytophthora niederhauserii has been detected in Santa Barbara County and counties within the San Joaquin Valley namely, Kings, Fresno, Kern, Merced, Stanislaus, Madera, San Luis Obispo and Tulare counties (CDFA Plant Pathology Database, 2007; Schmidt et al., 2012).

California Interceptions:  The pathogen has not been intercepted in quarantine shipments of plants.

The risk Phytophthora niederhauserii would pose to California is evaluated below.

Consequences of Introduction: 

1)  Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) not likely to establish in California; or likely to establish in very limited areas
– Medium (2) may be able to establish in a larger but limited part of California
High (3) likely to establish a widespread distribution in California

Risk is High (3) Phytophthora niederhauserii has already been detected in few nurseries in California and has been reported (Schmidt et al., 2012) as an aggressive pathogen of almonds in the San Joaquin Valley of California.  Within California, it is likely to establish in cool, wet climates in susceptible hosts.

2)  Known Pest Host Range: Evaluate the host range of the pest:

– Low (1) has a very limited host range
– Medium (2) has a moderate host range
– High (3) has a wide host range

Risk is Medium (2) Currently at least 33 plant species in 25 families have been reported as hosts of the pathogen.  A number of shrubs and herbaceous ornamental plants are included. Few agricultural crops (almonds and grapes) are also included.  The latter are grown as major crops in California.

3)  Pest Dispersal Potential: Evaluate the dispersal potential of the pest:

– Low (1) does not have high reproductive or dispersal potential
– Medium (2) has either high reproductive or dispersal potential
High (3) has both high reproduction and dispersal potential

Risk is High (3) Phytophthora niederhauserii is primarily spread artificially via infested soils, plants, nursery and planting stock, seedlings, run-off and splash irrigation water, cultivation equipment and tools that may spread contaminated soil and plant materials to non-infected sites.

4)  Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

A.   The pest could lower crop yield.
B.   The pest could lower crop value (includes increasing crop production costs).
C.   The pest could trigger the loss of markets (includes quarantines).
D.   The pest could negatively change normal cultural practices.
E.   The pest can vector, or is vectored, by another pestiferous organism.
F.   The organism is injurious or poisonous to agriculturally important animals.
G.   The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts
– Medium (2) causes 2 of these impacts
High (3) causes 3 or more of these impacts

Risk is High (3) – The pathogen could lower crop yield, increase production costs and cause loss of market of infected nursery stock and agricultural crops. The capability of the pathogen to survive and spread in infected soils and irrigation water could require changes in normal cultivation practices of host plants.

5)  Environmental Impact: Evaluate the environmental impact of the pest on California using these criteria:

A.   The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B.   The pest could directly affect threatened or endangered species.
C.   The pest could impact threatened or endangered species by disrupting critical habitats.
D.   The pest could trigger additional official or private treatment programs.
E.   The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

– Low (1) causes none of the above to occur
– Medium (2) causes one of the above to occur
High (3) causes two or more of the above to occur

Risk is High (3) – A number of plants in natural ecological habitats are hosts to the pathogen.  Subsequently, natural plant communities, ecosystems, threatened or endangered species as well as home/urban gardening and ornamentals may be negatively impacted.

Consequences of Introduction to California for Phytophthora niederhauserii:

Add up the total score and include it here. (Score)

Low = 5-8 points
Medium = 9-12 points
High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Phytophthora niederhauserii to California = (14).

6)  Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.
-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is High (-3). In California, Phytophthora niederhauserii has been detected in Santa Barbara County and the San Joaquin Valley counties.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11.


Statewide surveys specifically for Phytophthora niederhauserii have not been conducted to include all nursery sites and natural ecosystems (e.g., restoration sites) as well as almond and grapevine cultivation sites.  Subsequent data generated may result in the addition of new host plant species and further distribution of the pathogen within California.  All this may alter the current proposed rating of P. niederhauserii.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phytophthora niederhauserii is B.


Abad Z. G, and J. A. Abad.  2003.  Advances in the integration of morphological and molecular characterization in the genus Phytophthora: the case of P. niederhauseria sp.nov. Phytopathology 408 93:S1.

Abad, Z. G., J. A. Abad, S. O. Cacciola, A. Pane, R. Faedda, E. Moralejo, A. Pérez-Sierra, P. Abad-Campos, L. A. Alvarez-Bernaola, J. Bakonyi, A. Józsa, M. L. Herrero, T. I. Burgess, J. H. Cunnington, I. A. Smith, Y. Balci, C. Blomquist, B. Henricot, G. Denton, C. Spies, A. Mcleod, L. Belbahri, D. Cooke, K. Kageyama, S. Uematsu, I. Kurbetli and K. Keğirmenci.  2014.  Phytophthora niederhauserii sp. nov., a polyphagous species associated with ornamentals, fruit trees and native plants in 13 countries.  Mycologia, 106 (3): 431-447.

Agrios, G. N.  2005.  Plant Pathology fifth edition.  Elsevier Academic Press, Massachussetts, USA.  922 p.

Farr, D.F., & Rossman, A.Y.  2014.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved November 10, 2014, from

Jo´zsa A, J. Bakonyi, L. Belbahri, ZA Nagy, A. Szigethy, G. Boha´r and S.Woodward. 2010. A new species of Phytophthora reported to cause root and collar rot of common boxwood, Nordmann fir and Port Orford cedar in Hungary. Plant Pathology 59:1166–1167.

Pe´rez-Sierra A, A. Leo´n, LA A´ lvarez, S.Alaniz, M. Berbegal, J. Garcı´a- Jime´nez, P. Abad-Campos. 2010. Outbreak of a new Phytophthora sp. associated to severe decline of almond trees in eastern Spain. Plant Disease 94:534–541.

Robayo-Camacho E, Hwang J, Jeffers SN.  2009.  A diversity of species of Phytophthora found on floriculture crops.  Phytopathology 99:S109, doi:10.1094/PHYTO-99-1-0109

Schmidt, L. S., R. G. Bhat, D. A. Kluepfel and G. T. Browne.  2012.  Resistance to Phytophthora in new rootstocks for almond and stone fruits.  Phytopathology, 102:S4.106.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110,[@]


Comment Period:  CLOSED

The 45-day comment period opened on June 1, 2015 and closed on July 16, 2015.


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