Cercospora ruscicola

California Pest Rating for

Cercospora ruscicola V. G. Rao & A. S. Patil 1972

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

On April 28, 2017, a shipment of Ruscus (Ruscus sp.) plants with symptoms of leaf spots and destined to a private resident in Contra Costa County, was intercepted by Contra Costa County officials. The shipment had originated in Florida. A sample of diseased “leaves” was sent to the CDFA Plant Pathology Laboratory for diagnosis. On May 8, 2017, Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Cercospora ruscicola associated with the diseased leaf tissue. As there have not been any earlier reports of this pathogen in California, it was given a temporary ‘Q’ rating. Subsequently, the consequences of introduction and establishment of C. ruscicola in California is assessed and a permanent rating is proposed herein.

History & Status:

Background: The fungal pathogen, Cercospora ruscicola was originally identified from necrotic lesions on “leaves” (actually, ‘cladodes’ which are leaf-like modified stems) of several Ruscus plants at Poona, India (Rao & Patil, 1972). There have not been any further reports of the global spread of this species, however, Cercospora spp., including C. ruscicola have been detected in federally intercepted samples of Ruscus plants, according to USDA’s National Mycologist (personal communications: S. Latham, CDFA plant pathologist). Cercospora ruscicola is not known to be present in California. The recent detection of this species in intercepted plants from Florida marked a first record. Cercospora ruscicola is also known by its teleomorph (sexual) stage, Mycosphaerella ruscicola A. Pande 1980.

Disease development: 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: Ruscus aculeatus (butcher’s broom), Ruscus sp. (Farr & Rossman, 2017; Rao & Patil, 1972; CDFA Pest and Damage Record, May 8, 2017).

Symptoms: Similar to most other Cercospora diseases, symptoms caused by C. ruscicola are leaf spots. Spots may be irregularly circular to angular, with or without a distinct border, and usually coalesce to form extensive blighted regions. Rao and Patil (1972) observed extensive, irregular necrotic regions on leaves of Ruscus plants.

Damage Potential: Quantitative losses due to Cercospora ruscicola have not been reported. Photosynthetic area can be reduced due to leaf spotting. In severe infections, leaf wilt and drop may be expected. Rao and Patil (1972) stated that the “severe’ disease ultimately resulted in defoliation and blight of Ruscus plants in India. Generally, the damage potential due to this pathogen is likely to be similar to other Cercospora diseases which is usually low (Agrios, 2005).

Ruscus spp. are evergreen, perennial plants that are uncommon and not grown commercially in California, even though they are able to tolerate a wide range of temperatures, except freezing, and grow in shade under wet and dry conditions (Stamp, 2001). In California, they may be found in ornamental nurseries, and residential and public gardens where they may be at risk of infection and damage by Cercospora ruscicola. Furthermore, Ruscus stems and berries are used in dried or fresh floral arrangements. Damage caused by C. ruscicola may significantly impact commercial and private florist businesses.

Worldwide Distribution: Asia: India (Farr & Rossman, 2017; Rao & Patil, 1972).

Official Control: Presently, Cercospora ruscicola is on the ‘Harmful Organism’ list for Paraguay (USDA-PCIT, 2017).

California Distribution: Cercospora ruscicola is not known to be established in California.

California Interceptions: Cercospora ruscicola was detected in a single shipment of Ruscus sp. intercepted by Contra Costa County officials in April 2017 (see: ‘Initiating Event’).

The risk Cercospora ruscicola would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Ruscus are not commonly grown in California. However, they are able to grow in shade under wet and dry conditions and can tolerate a wide range of temperature (except freezing). These conditions enable the plants to grow in several areas in California and, if introduced, Cercospora ruscicola would be able to establish wherever its host plant is grown under high relative humidity/moisture and warm climate. However, as the plants are not commercially cultivated and are uncommonly grown in residential and public gardens and ornamental nurseries, the pathogen is given a low score in this category.

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

Score: 1

– 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: Presently, the host range is only limited to Ruscus and R. aculeatus in the family Ruscaceae.

Evaluate the host range of the pest.

Score: 1

– 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: Cercospora ruscicola has high reproductive potential resulting in the successive production of conidia which are dependent on air currents, infected plants, and seed for dispersal and spread.

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: Diseased Ruscus plants exhibiting leaf spot symptoms could result in lowered value of plants and loss of markets to nurseries and florist businesses. Increased costs of production can be expected with the necessary use of appropriate fungicides and other disease management strategies.

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

Economic Impact: B, C

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: 2

– 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.

4) Environmental Impact: The pathogen could significantly impact ornamental plantings in home/ urban, public gardens and other recreational environments.

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

Environmental 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.

Environmental Impact Score: 2

– 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 Cercospora ruscicola: Medium (9)

Add up the total score and include it here.

-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 ‘Not established’.

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: 9)

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 ruscicola is B.

References:

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

Farr, D. F., and A. Y. Rossman. 2017. Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved May 10, 2017, from http://nt.ars-grin.gov/fungaldatabases/

Rao, V. G., and A. S. Patil. 1972. Cercospora ruscicola sp. nov. from India. Transactions British Mycological Society, 58: 522.

Stamp, R. H. 2001. Florida/Holland/Israeli Ruscus production and use. University of Florida Extension, IFAS. Circular 1268 (ENH844).

USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. May 10, 2017, 12:21:55 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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