Pseudocercospora myrticola (Speg.) Deighton 1976

California Pest Rating for

Pseudocercospora myrticola (Speg.) Deighton 1976

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

None. The risk of infestation of P. myrticola in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background: Pseudocercospora myrticola is a fungal plant pathogen that belongs to a larger group of Cercospora-like fungi most of which cause leaf spot symptoms in host plants. The pathogen was originally named Cercospora myrticola, and since then has also been known by several synonyms: Cercospora myrti, C. saccardoana, C. amadelpha and Fusariella cladosporioides (Crous et al., 2013; Farr & Rossman, 2016). The pathogen is widely distributed globally and infects myrtle and several species within the family Myrtaceae, with few in Melastomataceae (Farr & Rossman, 2016). In the USA, P. myrticola has only been reported from myrtle (Myrtus communis). In 1984, P. myrticola was first reported in the USA from Florida (Alfieri et al., 1984) and from San Diego, California in 2006 (CPPDR, 2007). On December 4, 2013, the pathogen was detected in a decorative wreath comprising of symptomatic leaves of an unknown plant, most likely to be myrtle that had been shipped from the State of Nevada and intercepted in Sonoma County, California.

Disease cycle: 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. Sub-stomatal 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.

Hosts: Blepharocalyx divaricatus, Metrosideros excela (New Zealand Christmas tree), M. parkinsonii (Parkinson’s rata), Monochaetum polyneurum, Myrciaria cauliflora (jaboticaba), Myrtus communis (common myrtle), M. communis var. latifolia, M. communis var. laurifolia, M. divaricata, Tristania suaveolens (swamp mahogany) (Farr & Rossman, 2016).

Symptoms: Infected host plants exhibit irregular to angular, leaf spots on both leaf surfaces. Spots are 2-4 mm in diameter, rusty-brown, abundant on the lower leaf surface, usually confluent. Lesions or spots may be surrounded by a diffuse lighter halo (Nakashima et al., 2004).

Damage Potential: Specific losses due to Pseudocercospora myrticola 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). In California, myrtle is not native to California and is grown in lower coastal and some inner valley regions of the State (Calflora, 2016) in landscapes, commercial and private gardens. Also, young branches and foliage are used in floral decorations and therefore, diseased plants could be of particular concern to production nurseries.

Worldwide Distribution: Africa: South Africa, Cape Province; Asia: India, Japan; Europe: Cyprus, England, Republic of Georgia, Germany, Greece, Israel, Italy, Sicily, Scotland, Sweden, Yugoslavia; North America: USA (Florida, California); South America: Brazil, Chile, Paraguay; Oceania: Australia, New Zealand (Crous et al., 2013; Farr & Rossman, 2016).

Official Control: None reported. Presently, Pseudocercospora myrticola has a temporary ‘Q’ rating in California.

California Distribution: Pseudocercospora myrticola has been found in San Diego Counties (CDFA Plant Pest and Damage Records).

California Interceptions: Pseudocercospora myrticola was detected in 2013 in an intercepted quarantine shipment of a plant wreath that originated in Nevada.

The risk Pseudocercospora myrticola 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): Pseudocercospora myrticola may be able to establish wherever myrtle and other hosts plants are able to grow. Myrtle is a non-native plant in California and is grown in lower coastal and some inner valley regions in warm and humid climates.

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 Medium (2): Pseudocercospora myrticola has a moderate host range that comprises common myrtle and other species within Myrtaceae, plus few species in Melastomataceae.

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): Pseudocercospora myrticola 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 lower value of nursery-produced plants 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): Pseudocercospora myrticola infections could significantly impact home/urban gardening and aesthetic plantings of myrtle in commercial environments, such as parks and public gardens.

**Consequences of Introduction to California for Pseudocercospora myrticola:**

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 = 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 Low (-1): Pseudocercospora myrticola has been found in San Diego County only.

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:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pseudocercospora myrticola is B.

References:

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

Alfieri Jr., S. A., K. R. Langdon, C. Wehlburg, and J. W. Kimbrough. 1984. Index of Plant Diseases in Florida (Revised). Florida Department of Agriculture and Consumer Service, Division of Plant Industry Bulletin 11: 1-389. In [Farr, D. F. & A. Y. Rossman, 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved October 19, 2016, from http://nt.ars-grin.gov/fungaldatabases/ ].

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 lineages in Pseudocercospora. Studies in Mycology 75: 37-114.

Calflora. 2016. Information on California plants for education, research and conservation. [Web application]. Berkeley, California: The Calflora Database [a non-profit organization]. http://www.calflora.org/

CPPDR. 2007. Plant pathology A & Q rated pathogen & hosts detected by county. California Plant Pest & Disease Report, California Department of Food and Agriculture July 2005 through December 2006 23(1): 113-115.

Farr, D.F., & A. Y. Rossman. 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved October 19, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Nakashima, C., H. Horie, and T. Kobayashi. 2004. Addition and reexamination of Japanese species belonging to the genus Cercospora and allied genera. VI. Four Pseudocercospora species from Ohshima Island, Tokyo. Mycoscience 45: 49-55. DOI 10.1007/s10267-003-0151-y

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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