Phytophthora cactorum (Lebert & Cohn) J. Schröt. 1886

California Pest Rating Proposal for
Phytophthora cactorum (Lebert & Cohn) J. Schröt. 1886
Pest Rating: B

 


PEST RATING PROFILE
Initiating Event:

None.  The current risk and status of Phytophthora cactorum in California are reassessed and a permanent rating is proposed.

History & Status:

Background:  Phytophthora cactorum is an oomycete pathogen that has a very wide host range and can cause a wide range of disease symptoms including, root rot, collar and crown rot, fruit rot, and stem canker, usually in conjunction with other Phytophthora spp. in its hosts.  Phytophthora root and crown rot disease are among the most important soilborne diseases of stone fruits (Brown & Mircetich, 1995).  It is widespread in temperate regions of all continents and occurs in soils of natural forests, agricultural fields and orchards.  It can persist and spread in different environments and is capable of surviving in the soil as a saprophyte and by producing resting spores.

Phytophthora cactorum is widespread in California and has been found in several counties (see: “California Distribution”).  In California, P. cactorum has been found in several hosts: apple, avocado, apricot, American plum, European plum, Japanese plum, Myrobalan plum, sour cherry, sweet cherry, sweet almond, Mabaleb cherry, cherry laurel, peach, nectarine, pear, Southern California walnut, Northern California walnut, English walnut, strawberry, oval kumquat, sweet orange, kiwifruit, peony, rose, rhodendron, tomato, garden rhubarb, lilac, lily, calla lily, Didier’s tulip, tulip, garden snapdragon, western vervain, virbinum, blue blossom ceanothus, million bells, safflower, wild oats, daphne, white fir, Pacific madrone, chamise, manzanita, wild oats, coyote brush, incense cedar, beefwood, deodar cedar, eucalyptus, California buckthorn/coffeeberry, buckthorn, California flannelbush, toyon, common hop, holly, spicebush, carob, savin juniper, juniper, English laurel, redbay, Frasier’s photinia, chokeberry, Ponderosa pine, sticky cinquefoil, Formosa fire thorn, fire thorn, California live oak, valley oak, oak, cork oak, southern live oak, Indian hawthorn, redwood, giant sequoia, yew, and sticky monkey flower (French, 1989, CDFA Pest Damage Records).  The pathogen has also been recovered from various habitats including flowing water, stream and ditch banks, residential and public gardens, recreational areas, orchards, forests, and nurseries (Yakabe et al., 2009; CDFA Pest Damage Records).

Hosts: Phytophthora cactorum has a very wide host range of plants belonging to several families including, Aceraceae, Apocynaceae, Apiaceae, Araliaceae, Cactaceae, Cucurbitaceae, Cornaceae, Ebenaceae, Ericaceae, Fagaceae, Geraniaceae, Grossulariaceae, Hippocastanaceae, Juglandaceae, Lauraceae, Liliaceae, Oleaceae, Pinaceae, Proteaceae, Polygonaceae, Rutaceae, Rosaceae, Salicaceae, Solanaceae, Sterculiaceae, and Violaceae (CABI, 2017).

Farr and Rossman (2017) include 1332 records of hosts for Phytophthora cactorum and its synonyms.  Hosts include: Abies alba (silver fir), A. amabilis (Pacific silver fir), A. balsamea (balsam fir), A. balsamea var. phanerolepsis, A. concolor (white fir), A. firma (momi fir), A. fraseri (Fraser fir), A. magnifica var. shastensis (Shasta red fir), A. procera (noble fir), Abies sp., Acacia sp. (wattles/acacias), Acer spp. (maples), Actinidia chinensis (kiwi), A. deliciosa (fuzzy kiwifruit), Adenostoma fasciculatum (chamise), Aesculus hippocastanum (horse chestnut), Aesculus sp. (buckeye and horse chestnuts), Agonis flexuosa (Jervis Bay Afterdark), Alnus glutinosa (common alder/black alder), A. incana (grey alder/speckled alder), A. oregana (Oregon alder), Amygdalus persica (peach), Ananas comosus (pineapple), Anemone coronaria (poppy anemone/Spanish marigold), Angelica sp. (angelica), Annona cherimola (cherimoya), Antirrhinum sp., A. majus (snapdragon), Aquilegia sp. (columbine), Aralia cordata (spikenard), A. elata (Japanese angelica-tree), Arbutus menziesii (Pacific madrone/madrone), Arctostaphylos spp. (manzanita), Aster spp. (asters), Aucuba japonica (spotted laurel/Japanese laurel), Avena fatua (common wild oat), Baccharis pilularis (coyote brush),  Banksia spp. (banksia), Begonia sp. (begonia), Beta vulgaris var. crassa (beets), Betula lutea (yellow birch), B. pendula (silver birch), Betula sp. (birch), Boehmeria spp. (false nettles), Brassica oleracea var. bullata (Brussel sprouts), Brassica sp. (mustard), Brassolaeliocattleya sp. (orchid), Bryophyllum pinnatum (airplant), Buxus sp. (boxwood), Cactus sp., Calceolaria integrifolia (bush slipperwort), Calceolaria sp. (sweetshrub), Calibrachoa sp. (million bells), Callistephus chinensis (China aster), Calocedrus decurrens (California incense cedar), Calycanthus floridus (eastern sweetshrub), C. occidentalis (spicebush), Calytrix angulata (yellow starflower), Capsicum annuum (cayenne pepper), C. frutescens (chili pepper), Carica papaya (papaya), Carthamus tinctorius (safflower), Carya illinoinensis (pecan), Castanea sativa (sweet chestnut), Castanea sp., Casuarina sp. (beefwood), Catharanthus roseus (Madagascar periwinkle), Ceratonia siliqua (carob), Cereus spp., Cattleya sp. (cattleya orchid), Ceanothus thyrsiflorus (blue blossom ceanothus), Cedrus deodara (deodar cedar), Ceratonia siliqua (carob tree),  Chamaecyparis spp. (false cypress), Chrysalidocarpus lutescens (areca palm/butterfly palm), Chrysanthemum spp., Citrullus lanatus (watermelon; syn. C. vulgaris), Citrus aurantium (bitter orange), C. grandis (pomelo; syn. C. maxima), C. limon (lemon), C. limonia (Mandarin lime), C. sinensis (sweet orange), Citrus sp., Clarkia spp., Cleome spp.,  Cocos nucifera (coconut), Cornus sp. (dogwood), C. sericea (western dogwood), Cucumis  melo var. inodorus (Kolkhoznitsa melon), C. melo var. reticulatus (galia melon), C. sativus (cucumber), C. pepo (field pumpkin), Dahlia sp., Daphne cneorum (rose daphne/garden flower), D. mezereum (February daphne), D. odora (winter daphne), Daphne sp., Dendrobium sp. (dendrobium orchid), Dianthus caryophyllus (carnation), Daucus carota (carrot), Diospyros kaki (persimmon), Diplacus aurantiacus (syn. Mimulus aurantiacus, sticky monkeyflower), Eriobotrya japonica (loquat), Echinochloa crusgalli (barnyardgrass), E. eyriesii, Epidendrum spp. (Epidendrum orchids), Erica hyemalis (cape heath), Eucalyptus spp., Fagus sp. (beeches) F. sylvatica (common beech), Fragaria spp. (strawberry), F. ananassa (strawberry), F. chiloensis (Chilean strawberry), F. vesca (wild strawberry), Frangula californica (coffeeberry/California buckthorn), Fraxinus spp., (ash), Fremontia californica (California flannelbush; syn. Fremontodendron californicum (California flannelbush), Fremontia sp., F. mexicanum (Mexican flannelbush), Fortunella margarita (oval kumquat), Galeandra baueri (orchid), Gladiolus sp., Glycine max (soybean), Hesperocyparis macrocarpa (syn. Cupressus macrocarpa, Monterey cypress), Heteromeles arbutifolia (toyon), Hibiscus spp. (rosemallows), Humulus lupulus (common hop), Ilex sp. (holly), Juglans californica (California black walnut), J. hindsii (Northern California walnut/Hinds’ black walnut), J. nigra (black walnut), J. pyriformis, J. regia (English walnut), Juglans sp., Juniperus procera (African juniper), J. sabina (savin juniper), Juglans. sp., Kalanchoe spp., Lactuca sativa (lettuce), Laeliocattleya sp. (orchid), Lilium spp. (lily), Lycopersicon esculentus (tomato; syn.  Solanum lycopersicum), Malus domestica (apple), Malus sp., M. sylvestris (European crab apple), Mespilus germanica (medlar), Panax quinquefolius (American ginseng), Pelargonium spp. (pelargonium), Paeonia lactiflora (Chinese peony/common garden peony), Paeonia spp. (peony), Panax spp. (ginseng), Persea americana (avocado), P. borbonia (redbay), Photinia spp. (photonia/chokeberry), Picea spp. (spruce), Pinus spp. (pine), Populus alba (silver-leaf poplar), Potentilla glandulosa (syn. Drymocallis glandulosa, sticky cinquefoil), Prunus armeniaca (apricot/American plum), P. avium (sweet cherry), P. cerasus (sour cherry), P. dulcis (almond; syn. P. amygdalus), P. ilicifolia (hollyleaf cherry/evergreen cherry), P. laurocerasus (cherry laurel/English laurel), P. mahaleb (mahaleb cherry), P. mume (Chinese plum/Japanese apricot), P. persica (peach), P. persica var. nucipersica (nectarine), P. salicina (Japanese plum), Prunus sp., Pyracantha coccinea (scarlet firethorn), , P. koidzumii (Formosa firethorn), Pyracantha sp. (fire thorn), Pyrus communis (European pear), Quercus agrifolia (California live oak/coast live oak), Q. falcata (southern red oak), Q. lobata (valley oak), Q. petraea (durmast oak), Q. robur, (English oak), Quercus sp., Q. suber (cork oak), Q. virginiana (live oak), Rhamnus (Frangula) californica (California coffeeberry), Rhaphiolepis indica (Indian hawthorn), Rheum rhaponticum (false rhubarb), Rheum hybridium (rhubarb), Rhododendron spp., (azalea), Ribes spp., (currants), R. lobbii (Lobbs gooseberry), R. uva-crispa (gooseberry), Rosa sp. (rose), Salix sp. ( willow), Sequoiadendron giganteum (giant sequoia), Solanum (nightshade), S. lycopersicum (tomato), Syringa vulgaris (lilac), Syringa sp., Taxus sp. (yew), Theobroma cacao (cocoa), Tulipa sp. (tulip), Tulipa gesneriana (Didier’s tulip), Viola sp. (violet), Vanda sp. (Vanda orchid), Verbena sp., V. lasiostachys (western vervain), Viburnum spp., Vicia faba (fava bean/broad bean), Vicia sp. (vetch), V. unguiculata, Vigna unguiculata (cowpea; syn. V. sinensis), V. cylindrica (catjang), V. sesquipedalis (yardlong bean), Vitis vinifera (grape ), Zea mays (corn), Zantedeschia sp. (calla lily) (CABI, 2017; Farr & Rossman, 2017; French, 1989; CDFA Pest Damage Records).

Symptoms: Phytophthora cactorum attacks a wide range of host plants causing varied symptoms, depending on the host.  Symptoms include root rot, collar and crown rot, fruit rot, stem cankers, leaf blight, wilts and seedling blights.  This pathogen can cause pre- and post-emergence damping-off disease in several plant species.  It has been reported to reduce sprouting and kill seedlings of beech, and cause seedling blight in Pinus spp., Salix scoulerana, and Robinia spp. (CABI, 2017).

On apple, pear and other woody hosts, P. cactorum causes crown, collar and root rot.  Crown rot affects rootstock tissue from the graft union down to the tips of the primary roots, whereas collar rot affects the scion above the graft union or slightly above the soil line.  Root rot refers to symptoms that appear beyond the proximal junction of primary roots to crown tissue (Cox, 2014).   Above ground symptoms are indicative of an impaired root system and include general stunting with reduced terminal growth and small, chlorotic leaves.  Symptom expression depends on the amount of infected crown or root tissue and their rate of destruction.  Young trees are usually killed by the pathogen since their root systems and crown regions are not as developed as those of mature trees.  Generally, crown rots advance rapidly and trees fall and die soon after the first warm spring.  Their leaves wilt, dry, and remain attached to the tree (Adaskaveg et al., 2009; Gubler & Teviotdale, 2009).  Trees with root rot slowly decline and eventually die over several seasons. At early stages of tree decline, removing the bark reveals orange to reddish brown necrotic lesions in cambium tissue.  A thin, dark delineated margin is evident at the junction of healthy tissue and the expanding lesion which, over time, turns dark brown as it gets colonized by secondary fungi and bacteria.  Symptoms can extend through the root system resulting in a lack of fibrous and feeder roots.  Crown lesions can extend to the primary roots and up to the graft union, while collar lesions can extend up to a meter up from the graft union.  On dissection, collar infections may appear striped in the inner phloem tissue and, sometimes, result in weeping though cracked barked tissue (Cox, 2014).   Phytophthora cactorum also causes fruit rot in apple and pear, producing pale olive and dark brown lesions in apple and pear respectively.  Those lesions are diffusely marbled or uniformly colored with softly delineated margins (Covey et al., 2014).

In Rhododendrons affected by Phytophthora root rot, roots become necrotic and leaves turn chlorotic, wilt, roll downwards parallel to the midrib, and eventually turn brown.  In contrast, leaves of infected azalea become chlorotic, and then necrotic, but seldom wilt. Necrotic leaves eventually drop to the ground (Hoitink et al., 2014).

Infected trees may develop cankers on the stem or near the soil line with discoloration of infected bark, sometimes extending into the internal tissues (CABI, 2017).

Phytophthora cactorum can cause crown rot and root rot of strawberries.  Initial symptoms typically include plant stunting and small leaves.  Later, infected plants may collapse rapidly or gradually.  When cut open, brown discoloration of the crown vascular tissue or entire tissue is apparent.  While other Phytophthora species may be involved, P. cactorum is the most common species on strawberry (Koike et al., 2008).  Fruit is also infected by P. cactorum resulting in leather rot disease.  On green fruit, symptoms appear as dark brown areas or green areas with brown margins.  As the rot spreads, the entire fruit turns brown with a rough texture that appears leathery. Infected mature fruit may be slightly discolored or turn brown to dark purple.  Internally, vascular tissue to each seed is darkened, and in later stages of decay mature fruit becomes leathery.  Infected fruit have unpleasant odor and taste.  Under moist conditions, white mycelial growth may be present on the surface of fruit.  Green and mature fruit eventually become shriveled mummies (Ellis & Madden, 1998).

Disease development: P. cactorum can survive for several years, mainly as oospores (sexual spores) in soil and mummified fruit. The pathogen can also survive as chlamydospores (thick-walled asexual spores) (Erwin & Ribeiro, 1996) in orchard soil or mycelium in host tissue (Cox, 2014).  Similar to other Phytophthora spp., P. cactorum lives as a saprophyte in litter and in soil containing dead organic material and is favored by moist and moderate climates. In spring, and in saturated soil, oospores germinate to produce sporangia.  In free water, zoospores are produced within sporangia and liberated into water.  While oospores and chlamydospores form the primary inoculum, sporangia are the principal source of secondary inoculum (CABI, 2017).  Free water is required for infection, however, a high incidence of disease can occur with as little as 2 hours or less of wetness at 17-25°C.  Optimum temperature for infection is 21°C.   The most favorable temperatures for sporangia production are between 15 and 25°C, and optimally at 20°C.  No sporangia are produced at 10 and 30°C (Ellis & Madden, 1998).   Sporangia can germinate directly or indirectly by producing zoospores.  Zoospores allow a population to increase rapidly and disperse widely in films of free water.  Zoospores are expelled from sporangia under suitable temperature and moisture conditions and swim by means of their flagella towards their host in response to root exudates.  Once a zoospore comes in contact with a root it germinates producing a germ tube which penetrates the root directly under waterlogged soil conditions.   More mycelium develops and eventually, oospores (sexual spores) are produced and serve as resting structures that can survive for several years.  (CABI, 2017).

Transmission: Like most Phytophthora species, P. cactorum is soil-borne and water-borne and may be spread to non-infected sites through infected plants, nursery and planting stock, and seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment, tools, and boots.  Under high moisture and windy conditions, sporangia may be airborne and important in spread of diseases such as leather rot of strawberry.  The pathogen is not seed-borne but can be spread by infected seedlings and through soil or plant debris containing oospores or chlamydospores contaminating seed samples (CABI, 2017).  Furthermore, irrigation water from canals, rivers, and ponds can be contaminated with Phytophthora spp. (Brown & Mircetich, 1995).

Damage Potential: Specific crop losses caused by Phytophthora cactorum alone may be difficult to assess as more than one species of Phytophthora may cause diseases with symptoms similar to those caused by P. cactorum and may be present in infected hosts. Nevertheless, P. cactorum is a serious pathogen of a wide range of plant species. Infections of 88-97% apple and pear nursery stock material in commercial nurseries has been reported (Jeffers & Aldwinckle, 1988), and P. cactorum has been frequently detected in several ornamental nurseries within California (Yakabe et al., 2009).  Therefore, nurseries may be at risk and need to be monitored for this pathogen to ensure production and planting of disease-free nursery stock.

California’s native vegetation is also at risk of root and crown rot caused by P. cactorum and other Phytophthora spp., many of which are endemic (limited) to California, while some are rare, endangered, or threatened plants, e.g., Ribes spp. (currant/gooseberry), Monterey cypress, and Arctostaphylos spp. (manzanita) (Calflora, 2017; CNPS, 2017).  Introduction of Phytophthora species are a threat to plant health in Bay Area restoration sites, where nursery stock is planted for flood control or to mitigate environmental impacts.   Detections on madrone, toyon, oaks, sticky monkeyflower, and manzanitas in native stands indicate that P. cactorum is capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation.

Worldwide Distribution: Asia: China, India, Indonesia, Iran, Israel, Japan, Korea DPR, Republic of Korea, Laos, Lebanon, Malaysia, Pakistan, Philippines, Taiwan, Turkey, Vietnam; Africa: Egypt, Kenya, Morocco, Senegal, South Africa, Tunisia, Zimbabwe; North America: Bermuda, Canada, Mexico, USA; South America: Argentina, Brazil, Chile, Colombia, Peru, Uruguay, Venezuela; Europe: Austria, Belgium, Bulgaria, Croatia, Czech Republic, (former) Czechoslovakia, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, Netherlands, Norway, Poland, Romania, Russian Federation, Russia (European), Serbia, Slovenia, Spain, Sweden, Switzerland, United Kingdom; Oceania: Australia, New Zealand; Central America and Caribbean: Cuba, El Salvador, Trinidad and Tobago (CABI, 2017; EPPO, 2017).

In the USA, Phytophthora cactorum has been reported from California, Florida, Maine, Michigan, Minnesota, New York, North Carolina, Ohio, South Carolina, Tennessee, Virginia, Washington (CABI, 2017; EPPO, 2017).

Official Control:  Presently, Phytophthora cactorum is the “Harmful Organism Lists” for Egypt, French Polynesia, Guatemala, India, Israel, Lebanon, and Nicaragua, while, Phytophthora spp. is on the “Harmful Organism Lists” for Canada, French Polynesia, Mexico, Namibia, Seychelles, South Africa, and the Bolivarian Republic of Venezuela (USDA PCIT, 2017).

California Distribution: Phytophthora cactorum is widely distributed within California.  From 2001-July, 2017, the pathogen was detected in Alameda, Butte, Contra Costa, Imperial, Los Angeles, Marin, Merced, Monterey, Placer, Sacramento, San Diego, San Francisco, San Mateo, Santa Barbara, Santa Clara, Santa Cruz, Siskiyou, Solano, Sonoma, and Stanislaus Counties (CDFA Pest Damage Records).

California Interceptions:  None reported.

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

Consequences of Introduction: 

1) Climate/Host Interaction: Phytophthora cactorum has already established a large distribution under moist and cool to warm climates in California.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– 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.

2) Known Pest Host Range: The pathogen has a very wide host range.

Evaluate the host range of the pest.

Score: 3

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

High (3) has a wide host range.

3) Pest Dispersal Potential: Phytophthora cactorum, like other Phytophthora, has high reproductive capability under moist conditions.  It is dependent on moisture for spore dissemination and plant infection.  It is soilborne and may be spread to non-infected sites through infected plants, nursery and planting stock, and seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment, tools, boots, rivers, canals, and ponds.  Therefore, it is given a high rating in this category.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– 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. 

4) Economic Impact: Damage caused by Phytophthora cactorum alone may be difficult to assess as more than one species of Phytophthora may be associated with root and crown rot of host tree.  Nevertheless, cactorum is a serious pathogen affecting production of several economically important hosts including, apple, pear, stone fruits, strawberry, ornamentals, and California native plants.  Nursery productions could be at risk. Controlling the disease would include soil water management and use of resistant varieties, thereby requiring changes in cultural practices and increase in crop production costs.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, D, G

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.

Economic Impact Score: 3

– 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.

5) Environmental Impact: In conjunction with other Phytophthora, P cactorum may be a contributor to root and crown disease of environmental plants. California’s native vegetation is at risk of root and crown rot damage caused by P. cactorum and other Phytophthora spp.  Certain native plants are endemic (limited) to the State, while some are rare, endangered, or threatened.  The pathogen is capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation.  Its association alone and with other Phytophthora spp. in infected forest and native tree and shrub hosts could result in lowered biodiversity, disrupted natural communities, and critical habitats.  Also, it may significantly impact ornamental plantings and home/urban gardening.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: A, B, C, E

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.

Environmental Impact Score: 3

– 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.

Consequences of Introduction to California for Phytophthora cactorum:

Add up the total score and include it here. 14

-Low = 5-8 points

-Medium = 9-12 points

                        –High = 13-15 points

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.

Evaluation is:

Score: (-3)

-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.

 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

Uncertainty:  

None.

Conclusion and Rating Justification:

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


References:

Adaskaveg, J. E., J. L. Caprile, W. D. Gubler, B. L. Teviotdale.  2009.  Cherry: Phytophthora root and crown rot, pathogen: Phytophthora spp.  UCIPM Statewide Integrated Pest Management Program, University of California Agriculture & Natural Resources.  http://ipm.ucanr.edu/PMG/r105100711.html

Browne, G. T., and S. M. Mircetich.  1995.  Phytophthora root and crown rots.  In Compendium of Stone Fruit Diseases, Eds: J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu, and J. K. Uyemoto.  APS Press, The American Phytopathological Society. Pages 38-40.

CABI.  2017.  Phytophthora cactorum (apple collar rot) full datasheet.  Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/40953

Calflora.  2017.  Information on California plants for education, research and conservation. [Web application]. 2017. Berkeley, California. The Calflora Database [a non-profit organization].  http://www.calflora.org/

CNPS.  2017.  Inventory of rare and endangered plants of California (online edition, v8-03 0.38).  California Native Plant Society, Rare Plant Program. Website http://www.rareplants.cnps.org [accessed 10 August 2017].

Covey, R. P. Jr., and D. C. Harris; revised by K. Cox.  2014.  Phytophthora fruit rot.  In Compendium of Apple and Pear Diseases and Pests Second Edition Eds. T. B. Sutton, H. S. Aldwinckle, A. M. Agnello, J. F. Walgenbach.  APS Press, The American Phytopathological Society.  Pages 41-42.

Cox, K.  2014.  Phytophthora collar, crown, and root rots.  In Compendium of Apple and Pear Disease and Pests Second Edition Eds: T. B. Sutton, H. S. Aldwinckle, A. M. Agnello, J. F. Walgenbach.  Pages 63-65.

EPPO.   2017.   Phytophthora cactorum (PHYTCC).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  https://gd.eppo.int/

Ellis, M. A., and L. V. Madden.  1998.  Leather rot.  In Compendium of Strawberry Diseases Second Edition Ed. J. L. Maas.  APS Press, The American Phytopathological Society.  Pages 33-35.

Erwin, D. C., and O. K. Ribeiro.  1996.  Phytophthora Diseases Worldwide. St Paul, Minnesota, USA: American Phytopathological Society Press.

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved July 31, 2017, from https://nt.ars-grin.gov/fungaldatabases/

French, A.M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Gubler, W. D., and B. L. Teviotdale.  2009.  Apple, Phytophthora root and crown rot (updated 3/2009).  UCIPM, University of California Agriculture & Natural Resources, Statewide Integrated Pest Management Program.  http://ipm.ucanr.edu/PMG/r4100511.html

Hoitink, D. M. Benson, and A. F. Schmitthenner; revised by D. M. Benson and S. N. Jeffers.  2014.  Phytophthora root rot.  In Compendium of Rhododendron and Azalea Diseases and Pests Second Edition Eds: R. G. Linderman and D. M. Benson.  Pages 5-10.

Jeffers, S. N., and H. S. Aldwinckle.  1988.  Phytophthora crown rot of apple trees: sources of Phytophthora cactorum and P. cambivora as primary inoculum. Phytopathology, 78: 328-335

Mircetich, S. M., and M. E. Matherton.  1976.  Phytophthora root and crown rot of cherry trees.   Phytopathology 66: 549-558.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved June 6, 2017. 11:48:29 am CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Yakabe, L. E., C. L. Blomquist, S. L. Thomas, and J. D. MacDonald.  2009.  Identification and frequency of Phytophthora species associated with foliar diseases in California ornamental nurseries.  Plant Disease, 93: 883-890.


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, plant.health[@]cdfa.ca.gov.

Comment Period:

August 25, 2017 – October 9, 2017


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 PEST RATING: B


Posted by ls

2 thoughts on “Phytophthora cactorum (Lebert & Cohn) J. Schröt. 1886”

  1. Comments on the California Pest Rating Proposal for Phytophthora cactorum

    Submitted by, Susan Frankel, USDA Forest Service, Pacific Southwest Research Station, Albany

    To help inform the revision of the pest risk rating for Phytophthora cactorum, I wanted to share some 2016 detections of P. cactorum in Southern California, on native plant nursery stock being grown for or recently outplanted in restoration areas. The detections highlight problems that the USDA Forest Service is encountering in preventing Phytophthora introductions into wildlands.

    Due to concerns over Phytophthoras in Bay Area restoration sites, botanists on the Angeles National Forest conducted a preliminary assessment of Phytophthora presence in 7 nurseries growing native plant nursery stock under contract for use to restore areas disturbed due to utility corridor construction and repair (pipelines and powerlines). Nursery stock was effluent baited and P. cactorum was detected in 3 of the nurseries associated with the following species: Quercus agrifolia (coast live oak), Heteromeles arbutifolia (toyon), Cercocarpus betuloides (Mountain Mahogany), and Salvia mellifera (black sage).

    One of the commercial native plant nurseries refused the Forest Service’s request to visit, so samples were collected at sites where their stock had recently been planted. P. cactorum was isolated from dead, Quercus john-tuckeri (Tucker’s oak) and also from outplanted Quercus agrifolia.
    In addition to P. cactorum, new or new hybrid Phytophthoras were detected in the nurseries and at some outplanted sites. But since the focus here is on P. cactorum, I will not detail those further.

    While we do not know the implications of these P. cactorum detections, as you note in this pest risk rating, P. cactorum is “a serious pathogen of a wide range of plant species” and “the pathogen is capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation. Its association alone and with other Phytophthora spp. in infected forest and native tree and shrub hosts could result in lowered biodiversity, disrupted natural communities, and critical habitats.”

    As this case demonstrates, the USDA Forest Service is faced with a difficult situation. Current regulatory control or conventions for phytosanitary standards are placing the Angeles NF at risk for future plant health damage; we cannot rely on commercial stock as clean. The stock is being planted in areas that support threatened species, so the tolerance for pathogen introduction is very low since it could jeopardize critical habitat.

    While the proposed increased rating from “C” to “B” is a step in the right direction, it alone will not provide the protection needed to prevent P. cactorum or other plant pathogen introductions to wildlands.

    Additional information for the P. cactorum risk assessment. The number of states listed as areas where P. cactorum has been detected seems low. A good source of information is the USDA ARS Fungal databases, where 1413 records of P. cactorum and its synonyms are listed. (Farr, D.F., & Rossman, A.Y. Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved September 12, 2017, from https://nt.ars-grin.gov/fungaldatabases/).

    Note. The risk assessment states that P. cactorum has a “widespread” distribution, and I agree with that judgement. However, “widespread” does not mean that this pathogen is “ubiquitous.” There are many wildland areas where P. cactorum is not present and those natural areas require protection from pathogen introduction on nursery stock or other commercial means.

    Thank you for this opportunity to comment. Please let me know if I may be of further assistance.

  2. Date: September 25, 2017

    From: Phytophthoras in Native Habitats Work Group, http://www.calphytos.org
    (contact: Janice Alexander, jalexander@ucanr.edu)

    To: John Chitambar, Plant Pathologist, CDFA

    Subject: Comments on California Pest Rating Proposal for Phytophthora cactorum

    The Phytophthoras in Native Habitats Work Group is pleased that the CDFA is reassessing the pest risk ratings of several Phytophthora species; we appreciate the opportunity to comment as proposed revisions become available. Here we comment on the posted California Pest Rating Proposal for Phytophthora cactorum which would change the current “C” rating to the proposed “B” rating.

    Overall, we see the change in the rating from “C” to “B” as beneficial as it elevates the rating to recognize that P. cactorum is of known “economic importance and is subject to: eradication, containment, control or other holding action at the discretion of the individual county agricultural commissioner”.

    In the risk rating proposal, the distribution and host list provided for P. cactorum is extensive and we agree that it demonstrates that this organism is “capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation.” Yakabe’s 2009 report of P. cactorum’s frequent detection in several California ornamental nurseries describes an on-going concern since nursery stock can be shipped both short- or long-distances and when outplanted provides a direct pathway for plant pathogen introduction.

    Similarly, P. cactorum was the most commonly detected Phytophthora species in California native plant nurseries and restoration sites based on the January 2014 to January 2016 analyses by the California Department of Food and Agriculture laboratory that confirmed this pathogen on 15 different native plant genera (Rooney-Latham et al. 2017). Due to its frequent detection in native plant nurseries, it is likely to be outplanted, where it is very likely to cause damage since many known host species are present in California’s natural environment; new introductions are likely to not be benign.

    We point out the need for a change in 5) Environmental Impact. The proposal notes that P. cactorum meets 4 environmental impact criteria: A, B, C, and E. (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. E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings).

    We believe it also meets the criteria for “D. The pest could trigger additional official or private treatment programs”. The basis for our appeal to add criteria “D” is, detections of P. cactorum on outplanted coyote ceanothus (Ceanothus ferrisiae), an endangered plant, caused the Santa Clara Valley Water District to initiate control treatment (Swiecki and Bernhardt 2017) which cost an estimated $900 per failed planting basin in a wildland mitigation site. This situation demonstrates the significance of the introduction of a soil-borne pathogen to an extremely rare plant species that is limited to only three known populations in the wild.

    Note on P. cactorum intraspecific diversity and variation. We call your attention to Tyler Bourret’s recent work (tbbourret@ucdavis.edu) on phylogenetic diversity within P. cactorum. Bourret reports that in studies conducted by David Rizzo’s UC Davis laboratory, “During a sudden oak death-related monitoring project, P. cactorum has been detected in Phytophthora stream baiting of Californian coastal waterways, but only from northern Humboldt and Del Norte counties despite sampling reaching south through San Luis Obispo county. These north coast stream isolates of P. cactorum were genetically distinct from the isolates found in Bay Area nurseries and restoration sites, and both groups are distinct from the intraspecific lineage known across the world as an agricultural pest (including those reported from California).” These distinctions are based on studies DNA sequences of highly variable mitochondrial genes, which allows some of the intraspecific lineages to be distinguished. Bourret also reports that a Bay Area restoration stream sample detected a strain of P. cactorum in an urban waterway (San Tomas Aquinas Creek, Santa Clara County) with riparian restoration outplantings; this isolate appears to be related to other restoration plant isolates rather than the north-coast stream isolates.

    Bourret’s detailed studies of intraspecific variation in genomes currently shows at least 3 distinct genetic variants of P. cactorum. Variations in pathogenicity in these variants has not yet been studied.

    P. cactorum is well known from a wide variety of angiosperm and gymnosperm hosts, and it is well documented that P. cactorum isolates from different plant hosts typically have distinct and unpredictable profiles with respect to which other plant hosts they might be capable of either infecting or killing (Erwin & Ribeiro 1996). It is unknown if this variation lies within subspecific lineages, or is more assigned to the individual Phytophthora isolate/strain. As a result, little can be predicted about any P. cactorum individual’s ability to cause widespread mortality in a particular native Californian plant, greatly increasing the risk of any individual introduction.

    Please let us know if we may be of further assistance. For more information on Phytophthoras in California native plant nurseries and restoration sites, see http://www.calphytos.org, or contact Janice Alexander, UC Cooperative Extension, Marin Co. We look forward to continuing to work with you to sustain plant health for California.

    References
    Erwin, D.C.; Ribeiro, O.K. 1996. Phytophthora diseases worldwide. American Phytopathological Society APS Press.
    Rooney-Latham, S.; Blomquist, C.L.; Soriano, M.C.; Guo, Y.Y.; Woods, P.; Kosta, K.L.; Weber, K.; Swiecki, T.J.; Bernhardt, E.A.; Suslow, K.; Frankel, S.J. 2017. An update on Phytophthora species in California native plant nurseries and restoration areas. In: Frankel, Susan J.; Harrell, Katharine M., tech. coords. Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 51.
    Swiecki, T.J.; Bernhardt, E.A. 2017. Testing and implementing methods for managing Phytophthora root diseases in California native habitats and restoration sites. In: Frankel, S.J.; Harrell, K.M., tech. coords. Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 53-55.
    Yakabe, L.E.; Blomquist, C.L.; Thomas, S.L.; MacDonald, J.D. 2009. Identification and frequency of Phytophthora species associated with foliar diseases in California ornamental nurseries. Plant Disease 93(9): 883-890.

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