Cercospora coniogrammes Crous & R. G. Shivas 2012

California Pest Rating for

Cercospora coniogrammes Crous & R. G. Shivas 2012

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

On June 14, 2016, a shipment of silver lady fern (Blechnum gibbum) plants from Florida, destined to a nursery in Nippomo, San Luis Obispo County, was intercepted by San Luis County officials. Diseased plants exhibiting leaf spot symptoms were collected and sent to the CDFA Plant Pathology Laboratory for disease diagnosis. Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Cercospora coniogrammes, by culturing and multigene sequencing. On July 19, 2016, the pathogen was detected in another shipment of silver lady fern plants from Florida and destined to the same nursery in San Luis Obispo County. The identity of the pathogen was confirmed on August 19, 2016 by the USDA PPQ PM National Identification Services in Beltsville, Maryland. This detection marked a new US record and is reportable/actionable by the USDA (Bowers, 2016). The pathogen was given a temporary Q rating and consequently, the shipment of Blechnum gibbum was placed on hold, treated with fungicides, and is currently undergoing 30-day inspections (Schnabel, 2016). The risk of infestation of C. coniogrammes in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background: Cercospora coniogrammes is a fungal pathogen that causes leaf spots on fern. The pathogen was first reported in 2012 from infected bamboo fern, Coniogramme japonica var. gracilis, in Brisbane, Queensland, Australia (Groenewald et al., 2012), and in 2016 from Brazil (Guatimosim et al., 2016). The detection of C. coniogrammes in California marked a new record of the pathogen in the USA (Bowers, 2016; see ‘Initiating Event’). Presently, not much is known about the distribution and ecology of the pathogen.

Disease cycle: In general, in infected plants, Cercospora species 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: air-currents, infected nursery plants, infected leaves, seeds (Agrios, 2005).

Hosts: Fern species, namely, Blechnum gibbum, Coniogramme japonica var. gracilis, Hypolepis mitis, Macrothelypteris torresiana (Groenewald et al., 2012; Guatimosim et al., 2016).

Symptoms: Infected host plants exhibit leaf spots on upper and lower sides of leaves and are sub-circular to angular, 1-3 mm in diameter, grey to pale brown, surrounded by a broad brown margin up to 4 mm in diameter (Groenewald et al., 2012).

Damage Potential: Quantitative losses due to Cercospora coniogrammes have not been reported. Photosynthetic area can be reduced due to leaf spotting. In severe infections, leaf wilt and drop may be expected. However, damage potential due to this pathogen is likely to be similar to other Cercospora diseases which is usually low (Agrios, 2005).

Worldwide Distribution: Australia: Queensland; South America: Brazil; North America: USA (Groenewald et al., 2012; Guatimosim et al., 2016).

Official Control: None reported particularly for Cercospora coniogrammes, however, the following countries have Cercospora spp. on their ‘Harmful Organism Lists’: French Polynesia, Madagascar, South Africa, and Sri Lanka (USDA PCIT, 2016).

California Distribution: Cercospora coniogrammes is not known to be established in California. Interceptions of infected plants in a San Luis Obispo nursery were placed on hold, treated with fungicide, and is currently undergoing 30-day inspections (see, ‘Initiating event’).

California Interceptions: Cercospora coniogrammes was detected in only two shipments of Blechnum gibbum intercepted by San Luis Obispo County officials during June and July 2016.

The risk Cercospora coniogrammes 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 Medium (2): Cercospora coniogrammes may be able to establish in large but limited regions in California wherever fern plants are able to grow naturally under high humid and cool to warm temperatures. Silver lady fern, Blechnum gibbum, is cultivated indoors and outdoors in coastal parts of California.

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): Presently, the host range for Cercospora coniogrammes is limited to few species of fern, namely, Blechnum gibbum, Coniogramme japonica var. gracilis, Hypolepis mitis, and Macrothelypteris torresiana.

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): Cercospora coniogrammes has high reproductive potential resulting in the successive production of conidia which are dependent on air currents and infected plants and seed for dispersal and 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 Medium (2): Infected host plants with leaf spot symptoms could result in lowered value and loss of markets of nursery-produced fern 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 Low (1): The pathogen could significantly impact ornamental plantings in home/ urban and commercial gardens and recreational environments.

Consequences of Introduction to California for Cercospora coniogrammes:

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. (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 not established (0): Cercospora coniogrammes is not established in California and has only been detected in intercepted shipments of fern to the State.

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:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Cercospora coniogrammes is B.

References:

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

Bowers, J. H. 2016. Email from J. H. Bowers, USDA, to H. R. Wright, USDA APHIS, forwarded to U. Kodira, CDFA on September 2, 2016.

Farr, D.F., & A. Y. Rossman. 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved September 22, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Groenewald, J. Z., C. Nakashima, J. Nishikawa, H. D. Shin, J. H. Park, A. N. Jama, M. Groenewald, U. Braun, and P. W. Crous. 2013. Species concepts in Cercospora: spotting the weeds among the roses. Studies in Mycology 75: 115-170.

Guatimosim, E., P. B. Schwartsburd, R. W. Barreto, and P. W. Crous. 2016. Novel fungi from an ancient niche: cercosporoid and related sexual morphs on ferns. Persoonia 37: 106-141.

Schnabel, D. L. 2016. Email from D. L. Schnabel, CDFA Pest Exclusion, to J. Chitambar, CDFA on September 28, 2016.

USDA PCIT. 2016. USDA Phytosanitary Certificate Issuance & Tracking System. Sept. 23, 2016. 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.