Category Archives: Fungi

Phytophthora hedraiandra de Cock & Man in’t Veld

California Pest Rating for
Phytophthora hedraiandra de Cock & Man in’t Veld
Pest Rating: B

 


PEST RATING PROFILE
Initiating Event:

Recently, Suzanne Latham, CDFA plant pathologist, detected Phytophthora hedraiaindra in Arctostaphylos pumila samples that were collected from a nursery in Monterey County during an inspection related to an earlier detection of P. tentaculata.   In December 2014, the pathogen had also been detected in Arctostaphylos plants propagated in a nursery in Alameda County.  This nursery had requested the CDFA Plant Pathology Laboratory to test some Arctostaphylos plants for Phytophthora spp. before they were to be released for planting.  The nursery baited the water flow-through the potted plants with Rhododendron and Oregano tissue that were provided by the CDFA Lab and returned the same for analysis.  Suzanne Latham, CDFA plant pathologist, confirmed the detection of Phytophthora hedraiandra in culture from Rhododendron leaf baits.  The collection of official samples and trace forward investigations are currently in process related to this detection.  Phytophthora hedraiandra was initially detected in San Francisco, California 2013 on Arctopstaphylos plants.  Arctopstaphylos native plants extracted from a natural site in San Francisco were propagated at three different nurseries in San Francisco, Berkley, and Santa Cruz.  Similar to the 2014 incident, the water flow-through of potted Arctopstaphylos plants was baited with plant tissue which was then sent to the CDFA Lab for testing.  Cheryl Blomquist, CDFA plant pathologist, identified P. hedraiandra in the samples.  The detection was confirmed by the USDA Lab in Beltsville, Maryland. All potted plants were eventually destroyed.  Phytophthora hedraiandra currently has a Q rating that is herein reassessed for the proposal of a permanent rating.

History & Status:

Background: Since the discovery of Phytophthora ramorum, causal organism for the Sudden Oak Disease, there has been an increase of surveys throughout the world, for Phytophthora spp. which resulted in the identification of several new species, including P. hedraiandraPhytophthora hedraiandra was first discovered in 2001 on leaf spots of Viburnum sp. in the Netherlands (de Cock & Lévesque, 2004).

Hosts: The full host range of Phytophthora hedraiandra is yet not known.  Presently, only certain species of Rhododendron (azalea) and Viburnum are reported as susceptible hosts (CABI, 2014; EPPO, 2014).  Fagus sylvatica (common beech) is also listed as a host (CABI, 2014; Hejna, et al., 2014).  According to CDFA Plant Pathology Detection Records (2014-2015), Arctostaphylos spp. appears to be a new host for this pathogen.

Symptoms:  Plant symptoms caused by Phytophthora hedraiandra infections may vary with the infected host.  Symptoms in Viburnum include wilting, leaf spots, stem cankers and root and collar rots, while symptoms in Rhododendron include leaf lesions and shoot dieback (Henricot & Waghorn, 2014; Schwingle, et al., 2006, 2007).  Symptoms in Fagus sylvatica include root rot, leaf chlorosis and wilting (Hejna et al., 2014).

Damage Potential: Currently, there are no reports on quantitative economic losses in plant production caused by Phytophthora hedraiandra. However, infestations may result in significant damage and loss in production and stands of host plants by causing root and collar rots of infected plants. Nursery ornamentals and plants grown in natural ecosystems are particularly affected.  In general for Phytophthora spp., young seedlings of trees and annual plants may be killed within a few day, weeks or months (Agrios, 2005).

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 and rain water, cultivation equipment and tools that may spread contaminated soil and plant materials to non-infected sites (Yang et al., 2012).

Worldwide DistributionEurope:  Italy, Netherlands, Slovenia, Spain, United Kingdom; North America: USA; Oceania: Australia.

In the USA, Phytophthora hedraiandra has been found in California, Minnesota, and Virginia (CABI, 2014; EPPO, 2014).

Official Control:  None reported.

California Distribution:  Alameda, Monterey and San Francisco Counties (see ‘Initiating Event’).

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

The risk Phytophthora hedraiandra 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 hedraiandra has already been detected in few nurseries in 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. Score:

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

Risk is Low (1) The full host range of Phytophthora hedraiandra is yet not known.  Presently, only certain species of Rhododendron (azalea) and Viburnum, and Fagus sylvatica (common beech) are reported as susceptible hosts.  

3)  Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– 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 hedraiandra 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 the criteria below. Score:

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) – Although quantitative economic losses in plant production have not reported, the potential for infected plants to result in root and collar rot, canker, leaf lesions and shoot dieback could decrease stands on non-infected plants, increase production costs and cause loss of market of infected  nursery stocks. 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 the criteria below.

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. Score:

– 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 Medium (2) – Currently, the host range and geographic distribution of P. hedraiandra are not fully known.  The few known host plants (see ‘Hosts’ above) can be found in natural ecological habitats as well as in nursery environments.  Subsequently, under favorable climate conditions, natural plant communities and ecosystems, as well as home/urban gardening and ornamentals may be negatively impacted.

Consequences of Introduction to California for Phytophthora hedraiandra:

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 = (12).

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 Low (-1). To date, Phytophthora hedraiandra has been detected in three California coastal counties (Alameda, Monterey and San Francisco Counties) on the same host (Arctostaphylos spp.) under similar climate (coastal nurseries).

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:

The full host range and in-state distribution of Phytophthora hedraiandra is not currently known.  To date, in California, the pathogen has only been detected from Arctostaphylos plants propagated in nurseriesContinued statewide surveys for Phytophthora spp. occurring in nurseries and natural ecosystems (e.g. restoration sites) will contribute to the present knowledge of this pathogen group as well as that of P. hedraiandra.  Consequently, the current proposed rating of P. hedraiandra may be affected.  

Conclusion and Rating Justification:

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

References:

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

CABI.  2014.  Phytophthora hedraiandra datasheet (basic) report.  Crop Protection Compendium.  www.cabi.org/cpc/

de Cock A. W. A. M. and C. A. Lévesque. 2004. New species of Pythium and Phytophthora. Studies in Mycology 50: 481-487.

EPPO.  2014.  Phytophthora hedraiandra (PHYTHD).  European and Mediterranean Plant Protection Organization PQR database.  http://www.eppo.int/DATABASES/pqr/pqr.htm.

Farr, D.F., & Rossman, A.Y.  2014.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved November 10, 2014, from http://nt.ars-grin.gov/fungaldatabases/ .

Henricot, B. and I. Waghorn.  2014.  First report of collar and root rot caused by Phytophthora hedraiandra on Viburnum in the UK.  New Disease Reports 29:8. http://dx.doi.org/10.5197/j.2044-0588.2014.029.008.

Hejna M., K. Cerny, L. Havrdova, and M. Mrazkova.  2014.  First report of Phytophthora hedraiandra causing Rhododendron dieback and root rot of Common Beech in the Czech Republic.  Plant Disease 98:1,434.2.  http://dx.doi.org/10.1094/PDIS-04-14-0339-PDN

NAPPO.  2006.  Phytophthora hedraiandra de Cock & Man in’t Veld First detection of Phytophthora hedraiandra in the United States and North America.  North American Plant Protection Organization’s (NAPPO Phytosanitary Alert System): http://www.pestalert.org/viewNewsAlert.cfm?naid=4

Schwingle, B. W., J. A. Smith and R. A. Blanchette, S. Gould, and B. L. Blanchette.  2006.  First report of dieback and leaf lesions on Rhododendrons sp. caused by Phytophthora hedraiandra in the United States.  Plant Disease 90:109. http://dx.doi.org/10.1094/PD-90-0109A.

Schwingle, B. W., J. A. Smith and R. A. Blanchette.  2007.  Phytophthora species associated with diseased woody ornamentals in Minnesota nurseries.  Plant Disease 91:97-102.

Yang, X. P. A. Richardson, S. R. Ghimire, P. Kong, and C. X. Hong.  2012.  Phytophthora hedraiandra detected from irrigation water at a perennial ornamental plant nursery in Virginia.  Plant Disease 96:915.3.  http://dx.doi.org/10.1094/PDIS-07-11-0614-PDN.

Responsible Party:

Dr. 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:  CLOSED

The 45-day comment period opened on Thursday, April 9, 2015 and closed on May 24, 2015.


Pest Rating: B


Posted by ls

Kweilingia divina (Syd.) Buriticá 1998

California Pest Rating for
Kweilingia divina (Syd.) Buriticá 1998
Pest Rating: A

 


PEST RATING PROFILE
Initiating Event: 

In December 2014, Kweilingia divina was detected in a quarantine interception of bamboo leaves showing symptoms of rust, imported from Florida to California.  The detection was made by Contra Costa Agricultural Commissioner’s office inspector and the associated pathogen was identified by Suzanne Latham, CDFA plant pathologist. This rust fungus had also been intercepted in 2006 by Los Angeles County in a similar shipment of bamboo from Hawaii.  All infected plants were destroyed.  The risk of introduction and establishment of Kweilingia divina in California is evaluated here and a permanent rating is proposed.

History & Status:

Background:  The bamboo rust fungal pathogen, Kweilingia divina was originally ascribed as the type species of the genus Dasturella (D. divina) which was detected in infected bamboo leaves (Bambusa sp.) in 1943 (Mundkur & Kheswalla, 1943).  However, in 1998, Dasterulla divina was renamed Kweilingia divina.

Kweilingia divina requires two different kinds of hosts to complete its life cycle (heteroecious), producing two types of specialized spores on each host, namely urediniospores and teliospores on bamboo and spermatia (pycniospores) and aeciospores on its alternate host, Catunaregam spinosa (mountain pomegranata). The pycnial and aecial state are not known in the New World (Farr & Rossman, 2015).

Hosts: Several species of bamboo including, Bambusa balcooa, B. bambos, B. domestica, B. multiplex, B. mutabilis, B. oldhami, B. polymorpha, B. tulda, B. shimadai, B. tuldoides, B. vulgaris, Dendrocalamus brandisii, D. hamiltonii, D. latiflorus, D. longispathus, D. strictus, Ischurochloa stenostachya, Ochlandra scriptoria, O. travancorica, Oxtenanthera sp.,O. abyssinica, O. nigrociliata, Phyllostachys bambusoides,Pleioblastus sp., Pseudoxytenanthera ritcheyi, Pseudosasa japonica var. usawai, P. usawai, Shibataea kumasaca,  Thyrsostachys oliveri, T. sianensis, and the alternate, non-bamboo host Catunaregam spinosa (Blomquist et al., 2009; Cummins, 1971; Nelson & Goo, 2011; Farr & Rossman, 2015).

Symptoms: On bamboo, initial symptoms of infection are the presence of water-soaked, pinhead-sized flecks on the lower surface of leaves.  Soon yellowish-orange to brown, elongate, interveinal, linearly aligned fruiting structures (uredinia) develop and produce urediniospores.  On the corresponding side of the upper leaf surface, grayish-brown to dark brown lesions with yellowish halos for along the parallel veins.  Numerous lesions may develop on a leaf surface or coalesce to form larger areas of tan-colored necrotic blight. Over time, brownish black linear structures (telia) develop within the lesions on the lower leaf, either inside old, degenerating uredinia or separately.  Severely infected leaves defoliate prematurely (Nelson & Goo, 2011).  The alternate host, Catunaregam spinosa is not present in California but is native to tropical Southeast Asia and tropical Africa.

Damage Potential:  Bamboo is not a main cultivated crop in California.  However, bamboo plants are grown and sold mainly as nursery ornamentals and commercial plantings in private residences, public parks, amusement parks, and other environments.  The bamboo rust disease is a threat to these limited yet economically important regions where bamboo is grown in California.  Rusted bamboo leaves are not only aesthetically unsightly but also negatively impact plant growth.  Severe infestations of bamboo rust can result in defoliation and reduction in plant growth, vigor and stand.  Once established in California, containment and management of the rust pathogen will be difficult as infected leaves produce masses of air-borne spores enabling long-range spread and infection.

Transmission:  The pathogen is spread from plant to plant mainly by windblown spores.  Urediniospores can be transported over several hundred kilometers by strong winds and washed down by rain to available hosts.  Insects, animals, humans, and rain may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.

Worldwide Distribution: Asia: India, China, Hong Kong, Japan, Pakistan, Taiwan, Malaysia; Africa: Cote d’Ivoire, Ghana, Nigeria,    North America: Mexico, USA; Oceania: Australia, New Calendonia, Samoa; Caribbean Islands: Cuba, Dominican Republic, Jamaica, Puerto Rico, Trinidad and Tobago, West Indies, Virgin Islands; Central America: Costa Rica; South America: Brazil, Guyana, Colombia, French Guiana (Farr & Rossman, 2015).

In the USA it has been reported from the Hawaiian Islands (Oahu, Hawaii, Kauai, and Maui).  The detections in California resulted in the eradication of the disease (Blomquist et al., 2009; Nelson & Goo, 2011).

Official Control: None reported.

California Distribution:  Bamboo rust pathogen, Kweilingia divina, is not established in California.  All 2006 and 2014 intercepted shipments of infected bamboo plants were destroyed (see ‘Initiating Event’).

California InterceptionsKweilingia divina was intercepted in Los Angeles in 2006 and in Contra Costa County in 2014.

The risk Kweilingia divina 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)Kweilingia divina is able to establish a widespread distribution in California wherever bamboo is grown.

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

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

Risk is Low (1) The host range of Kweilingia divina is mainly limited to several species of bamboo. The alternate host does not exist in California.

3)  Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– 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) – The infective spores of Kweilingia divina namely, urediniospores, are produced in abundance and are spread to healthy plants mainly by wind. Insects, animals, humans, rain, and infected nursery plants  also aid in its spread.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

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) – Severe infestations of the bamboo rust pathogen could result in defoliation and reduction of plant growth, vigor and stand, and loss of markets. Nursery plantings are at risk being significantly impacted by the introduction of this pathogen. Without eradicative action subsequent to detection of bamboo rust-infected plants within greenhouse environments, there is the risk of spread to the outside environment. The spread of the rust pathogen would be difficult to manage due to its effective means of windblown transmission.

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

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. Score:

– 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) – Outbreaks of the disease could have significant impact on established bamboo ecosystems. Commercial bamboo plantings in public parks, resorts and plantings in private residences may be impacted by the bamboo rust pathogen subsequently triggering additional treatment programs.

Consequences of Introduction to California for Kweilingia divina

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 Kweilingia divina to California = (13).

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: Kweilingia divina is not established in California (0)

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 = 13

Uncertainty:

Future detection surveys for Kweilingia divina in nurseries and established bamboo groves are needed to gain further information of the probable introduction, establishment and distribution of this pathogen in California.  This information could alter the proposed rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Kweilingia divina is A.

References:

Blomquist, C. L., J. M. McKemy, M. C. Aime, R. W. Orsburn and S. A. Kinnee.  2009.  First report of bamboo rust caused by Kweilingia divina on Bambusa domestica in Los Angeles County, California.  Plant Disease 93: 201. http://dx.doi.org/10.1094/PDIS-93-2-0201A

Cummins, G. B. 1971.  The rust fungi of cereals, grasses and bamboos.  Springer-Verlag New York Inc.  570 p.

Farr, D. R., and A. Y. Rossman.  2015.  Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved March 18, 2015, from http://nt.ars-grin.gov/fungaldatabases/

Johnson, G. I.  1985.  Rust (Dasturella divina) of Bambusa spp. in Australia.  Australasian Plant Pathology 14:54-55.

Mundkur, B.B., and K. F. Kheswalla. 1943. Dasturella: A New Genus of Uredinales. Mycologia 35:201–206.

Nelson, S., and M. Goo.  2011.  Kweilingia rust of bamboo in Hawaii.  College of Tropical Agriculture and Human Resources, University of Hawaii at Mānoa. Plant Disease PD-74.

Responsible Party:

Dr. 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: CLOSED

The 45-day comment period opened on Tuesday,  April 7, 2015 and closed on May 22, 2015.


Pest Rating: A


Posted by ls

Colletotrichum orbiculare (Berk. & Mont.) Arx 1957

California Plant Pest Rating for
Colletotrichum orbiculare (Berk. & Mont.) Arx 1957
Pest Rating: B

 


PEST RATING PROFILE
Initiating Event:

None. A permanent rating for Colletotrichum orbiculare is proposed herein.

History & Status:

Background: Colletotrichum orbiculare is a fungal pathogen causing anthracnose disease of cucurbit plants particularly watermelon, cantaloupe, and cucumber. The species is often known by its synonymized scientific name, Colletotrichum lagenarium and belongs to the taxonomic family Glomerellaceae, within the phylum Ascomycota. C. orbiculare is the asexual (anamorph) stage of the pathogen. The sexual stage (telemorph) with the name Glomerella lagenarium has been reported but is rarely found in nature. Two distinct populations of the pathogen are known: one from watermelon (race 1) and the other from cucumber and melon (race 1 and 3) (Sitterly & Keinath, 1996).

Hosts: The pathogen commonly attacks members of the family Cucurbitaceae, especially melon and watermelon. Hosts include Althaea officinalis (marsh-mallow), Artocarpus heterophyllus (jackfruit), Benincasa hispida (wax gourd), Citrullus lanatus (watermelon), Cucumis melo (melon), Cucumis sativus (cucumber), Cucurbita maxima (giant pumpkin), C. moschata (pumpkin), C. pepo (ornamental gourd), Momordica charantia (bitter gourd) and Trichosanthes cucumerina var. anguinea (snake gourd) (CABI, 2014).

Symptoms: Host plants infected with Colletotrichum orbiculare exhibit symptoms of anthracnose and fruit rot. In California, except for seedless watermelon, anthracnose is unusual on cucurbit crops and can cause leaf, fruit, and/or stem lesions. On cucurbits, leaf spots are usually large (>10 mm diameter) and tan to pale brown with distinct margins. However on watermelon, these foliage lesions are dark brown to black. Brown or black lesions appear on fruit. These lesions grow to 20-30 mm diameter, become sunken, wrinkled and dark, with concentric rings of sub-surface, tiny, black, saucer-shaped asexual structures that containing spores or conidia (acervuli). In wet weather, pink or orange spores ooze from these asexual structures (CABI, 2014; UCIPM, 2008). Fruit is susceptible to infection approximately at the time of ripening and severely infected fruits are often tasteless or bitter and usually invaded by soft rotting bacteria and fungi (Agrios, 2005).

Damage Potential: Anthracnose disease caused by Colletotrichum orbiculare has recently been considered to be particularly important wherever cucurbits are cultivated under highly controlled conditions. High infections may cause formation of numerous leaf lesions and vine defoliation resulting in poor quality fruit and yield loss (Egel, 2014). Watermelon artificially inoculated with C. orbiculare (as C. lagenarium) caused up to 63% losses in yield (CABI, 2014).

Disease Cycle: The species has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on cucurbit plant residue in soil, on infected volunteer plants, and on or in cucurbit seed. During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers. Conidia are transmitted to host plants. Humid, wet, rainy weather is necessary for infection to occur. Condia germinate and grow optimally at 22-27°C and 100% relative humidity for 24 hours. These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem in transplants grown under controlled environments of greenhouses. Condia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue up to 72 hours after deposition. Symptoms are produced about 96 hours after infection. The sexual stage (telemorph) is rarely found in nature (Sitterly & Keinath, 1996).

Transmission: Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution: Colletotrichum orbiculare is widely distributed throughout the world and has been reported from several countries in Asia, Africa, North America, South America, Central America and Caribbean, Europe and Oceania. In the USA it has been found in Alabama, California, Colorado, Connecticut, Florida, Hawaii, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Minnesota, Mississippi, Nebraska, North Carolina, North Dakota, Oklahoma, Pennsylvania, South Carolina and Texas (CABI, 2014; Farr et al., 1989).

Official Control: Currently Israel, Chile and Jordan include Colletotrichum orbiculare on their Harmful Organism List.

California Distribution: in California, Colletotrichum orbiculare has been detected in a greenhouse in Tehama County (Koike et al., 1991).

Historically, it has also been detected in southern coastal region counties which include: San Benito, Monterey, San Luis Obispo, Santa Barbara, Ventura, Los Angeles, Orange and San Diego Counties (K. F. Baker Herbarium, CDFA in The California Plant Disease Host Index by A. M. French, 1989).

Details of the south coastal region detections are not available. Given the absence of reports on the field detection of the pathogen in California, it is likely that the south coastal region detections were mainly limited to greenhouses. On the other hand, those south coastal counties would share a similar climate including higher incidence of rainfall and wind driven rain necessary for infection and establishment of the disease.

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

The risk Colletotrichum orbiculare 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 Low (1) – Colletotrichum orbiculare requires humid, wet, rainy weather for conidia to infect host plants. This is a main reason why the pathogen has not been able to fully establish and spread under dry field conditions in California. It has, however, been detected in controlled greenhouse environments.

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

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

Risk is Moderate (2) – Although the host range for Colletotrichum orbiculare is mainly limited to members of the family Cucurbitaceae, plants, the cultivation of cucurbits, mainly melon and watermelon, is in significant acreage and of major importance in California.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

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) – The pathogen has high reproductive potential and conidia are produced successively. They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

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) – Under suitable climates, the pathogen could lower crop yield, value and trigger the loss of markets.

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

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. Score:

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 Medium (2) – The pathogen could significantly impact cultural practices, home gardening or ornamental plantings.

Consequences of Introduction to California for Colletotrichum orbiculare:

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 Colletotrichum orbiculare to California = (11).

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 Medium (-1). Colletotrichum orbiculare has been reported from counties in the California’s south coastal region however, details of those detections are not available. Given the absence of reports on the field detection of the pathogen in California, it is likely that the south coastal region detections were mainly limited to greenhouses. Nevertheless, those south coastal counties would share a similar climate including higher incidence of rainfall and wind driven rain necessary for infection and establishment of the disease.

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 = 10.

Uncertainty:

As discussed above, there is little to no verifiable evidence of the occurrence of Colletotrichum orbiculare in field environments within California. Such information may strengthen or lower the proposed rating for this pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose of cucurbits pathogen, Colletotrichum orbiculare is B.

References:

Agrios, G. N. 2005. Plant Pathology (Fifth Edition). Elsevier Academic Press, USA. 922 p.

CABI. 2014. Colletotrichum orbiculare datasheet report. Crop Protection Compendium. www.cabi.org/cpc/

Egel, D. S. 2014. Vegetable diseases: Anthracnose of cucumber, muskmelon, and watermelon. Purdue Extension BP-180-W, Purdue University. https://www.extension.purdue.edu/extmedia/BP/BP-180-W.pdf

Farr, D. F, G. F. Bills, G. P. Chamuris and A. Y. Rossman. 1989. Fungi on Plants and Plant Products in the United States. St. Paul, Minnesota, USA: APS Press, 1252 pp.

Kitterly, W. R., and A. P. Keinath. 1996. Fungal disease of aerial parts: Anthracnose. In ‘Compendium of Cucurbit Diseases’. Edited by T. A. Zitter, D. L. Hopkins, and C. E. Thomas, APS Press The American Phytopathological Society Minnesota, USA, p. 24-25.

Koike S. T., T. E. Tidwell, D. G. Fogle and C. L. Patterson. 1991. Anthracnose of greenhouse-grown watermelon transplants caused by Colletotrichum orbiculare in California. Plant Disease, 75(6):644.

UCIPM. 2008. Cucurbits anthracnose pathogen: Colletotrichum lagenarium. UCIPM Online, Statewide Integrated Pest Management Program, University of California Agriculture & Natural Resources. http://www.ipm.ucdavis.edu/PMG/r116101411.html

Responsible Party:

Dr. 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:  CLOSED

The 45-day comment period opened on Monday, March 16, 2015 and closed on Thursday, April 30, 2015.


Pest Rating: B


Posted by ls