Pseudocercospora theae

California Pest Rating for

Pseudocercospora theae (Cavara) Deighton 1987

Pest Rating: C

PEST RATING PROFILE

Initiating Event:

On March 6, 2018, the USDA APHIS PPQ requested State Regulatory Officials to review PPQ’s consideration of deregulation of the pathogen, Pseudocercospora theae at US ports of entry. A ‘Deregulation evaluation of established pests’ report prepared by PERAL was provided for this review. Therefore, the risk of infestation of P. theae in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background: Pseudocercospora theae is a fungal plant pathogen in the Mycosphaerellaceae family, that causes leaf spotting known as, bird’s eye spot disease of tea (Camellia spp.). The pathogen has previously been known by its synonyms, Septoria theae and Cecoseptoria theae (Braun et al., 2012; Farr & Rossman, 2018). Holliday (1980) reported that the fungus causes a “very minor” leaf-spotting disease in tea plants.

Pseudocercospora theae has not been reported in California. In the USA, the pathogen has been reported in Florida since about 1955 and disease caused by P. theae has not been reported after 1998. It is likely that the pathogen is present at non-detectable levels and kept under control by standard disease management practices in nurseries (PPQ, 2018).

Disease cycle: While information on the specific biology of Pseudocercospora theae is limited, it is likely that its disease cycle is like that of other members of the genus. Generally, Pseudocercospora-infected plants produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia (asexual spores) successively. Conidia are easily detached and blown by wind often over long distances. On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host. Substomatal stroma (compact mycelial structure) may form from which conidiophores develop. Development of the pathogen is favored by high temperatures and the disease is most destructive during summer months and warmer climates. High relative humidity is necessary for conidial germination and plant infection. The pathogen can overwinter in or on seed and as mycelium (stromata) in old infected leaves (Agrios, 2005).

Dispersal and spread: Specific information for Pseudocercospora is lacking, however, its mode of dispersal is likely to be like other species of the genus and include air-currents, rain splash/drops, infected plants and propagative material (PPQ, 2018).

Hosts: Camelia sp., C. japonica (Japanese camellia), C. sasanqua (sasanqua camellia), C. sinensis (tea tree; synonyms: Thea assamica, T. sinensis) (Farr & Rossman, 2018). Although some species of Pseudocercospora are capable of infecting different hosts within a single family (Crous, et al., 2013), there is no evidence that this is true for P. theae (PPQ, 2018).

Symptoms: Infected host plants exhibit circular leaf spots no greater than 2-3 mm diam., on both sides of a leaf. The spots are at first purple red, with an indefinite yellow green border and turn white with a narrow purple red ring (Holliday, 1980) with a narrow, raised rim, followed by a dark marginal line or halo (Braun et al., 2012).

Damage Potential: Specific losses due to Pseudocercospora theae have not been reported. Ornamental plantings of Camellia species may be affected in limited regions of California with sufficient moisture for pathogen infection and development. The climatic suitability of the pathogen encompasses Hardiness Zones 10-13 (PPQ, 2018; Margery et al., 2008). Nursery production of Camellia species under controlled and conducive conditions for pathogen development would also be of concern in California. However, P. theae outbreaks in Florida nurseries were successfully controlled by use of proper sanitation practices and fungicide applications (PPQ, 2018), therefore, it is likely that the same will be true for California. If left uncontrolled, leaf spotting may lead to disease outbreaks under favorable conditions, wherein photosynthetic areas can be reduced, and in severe infections, leaf wilt and drop may be expected.

Worldwide Distribution: Asia: Nepal, Indonesia, India, China, Taiwan, Pakistan, Sri Lanka, Vietnam; Africa: Ethiopia, Malawi, Mauritius, Tanzania, Uganda; Europe: Georgia, Italy, Netherlands Antilles; North America: Florida; South America: Argentina, Brazil, Peru (Braun et al., 2012; EPPO, 2018; Farr & Rossman, 2018).

Official Control: Presently, Pseudocercospora theae is on the ‘Harmful Organism’ list for Colombia (USDA PCIT, 2018).

California Distribution: Pseudocercospora theae has not been reported from California. The pathogen is not known to be established in California.

California Interceptions: None reported.

The risk Pseudocercospora theae would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Limited parts of California with adequate moisture, as in coastal regions of the State where Camellia species are grown, are likely to favor establishment of Pseudocercospora theae.

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 host range is limited to Camellia [Camelia , C. japonica (Japanese camellia), C. sasanqua (sasanqua camellia), C. sinensis (tea tree)]

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.

3) Pest Dispersal Potential: Reproduction is high and dispersal conidia is through windborne conidia, and rain splash or raindrops. The pathogen is also spread through infected plant propagative material.

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: Specific losses due to Pseudocercospora theae have not been reported. Ornamental plantings of Camellia species may be affected in limited regions of California with sufficient moisture for pathogen infection and development. Nursery production of Camellia species under controlled and conducive conditions for pathogen development would also be of concern in California. However, theae outbreaks in Florida nurseries were successfully controlled by use of proper sanitation practices and fungicide applications (PPQ, 2018), therefore, it is likely that the same will be true for California. Uncontrolled infected plants may lose value, however, with control measures adopted, the impact is expected to be low.

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

Economic Impact: B

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.

5) Environmental Impact: Home garden plantings of Camellia species may be impacted if the pathogen was to establish under favorable environmental conditions and in the absence of adequate disease control.

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

Environment Impact: 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.

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.

Consequences of Introduction to California for Pseudocercospora theae: 9

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 to California = 9

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 ‘Not established’ in California.

Score: (0)

–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 = 9

Uncertainty:

There is very limited information available on the biology of Pseudocercospora theae.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pseudocercospora theae is C.

References:

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

Braun, U., M. Rybak, R. Rybak, and M. G. Cabrera. 2012. Foliar diseases on tea and mate in Argentina caused by Pseudocercospora species. Plant Pathology & Quarantine 2 (2): 103-110. Doi 10.5943/ppq/2/2/2

Crous, P. W., U. Braun, G. C. Hunter, M. J. Wingfield, G. J. M. Verkley, H. -D. Shin, C. Nakashima and J. Z. Groenewald. 2013. Phylogenetic lineage in Pseudocercospora. Studies in Mycology 75: 37-114. Published online: 22 May 2012; doi:10.3114/sim0005. Hard copy: June 2013. www.studiesinmycology.org

EPPO. 2018. Pseudocercospora theae (CERSTH). PQR database. Paris, France: European and Mediterranean Plant Protection Organization. https://gd.eppo.int/

Farr, D.F., & A. Y. Rossman. 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved August 1, 2016, from http://nt.ars-grin.gov/fungaldatabases/

Holliday, P. 1980. Fungus diseases of tropical crops. Cambridge University Press, New York. 607 pp.

PPQ. 2018. DEEP report for Pseudocercospora theae (Cavara) Deighton (Mycosphaerellaceae: Capnodiales) – Bird’s eye spot. United States Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine (PPQ), Raleigh, NC. 4 pp.

USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved March 21, 2018. 6:36:50 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

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.

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