California Pest Rating for
Pseudocercospora smilacicola U. Braun, 2014
Pest Rating: B
PEST RATING PROFILE
On July 21, 2016, a shipment of lance leaf greenbrier (Smilax sp.) plants from Texas, destined to a wholesale plant company in Santa Barbara, was intercepted by the Santa Barbara County officials. Diseased plants exhibiting leaf spot symptoms were collected and sent the CDFA Plant Pathology Laboratory for disease diagnosis. The fungal pathogen, Pseudocercospora smilacicola, was identified as the cause for the leaf spots, by Cheryl Blomquist, CDFA plant pathologist. This pathogen was also detected on March 23, 2016 and September 30, 2015, from Smilax sp. plant shipments that had originated in Texas and were destined for wholesale plant companies in Santa Barbara and Riverside Counties respectively. The pathogen was given a temporary Q rating. The risk of infestation of P. smilacicola in California is evaluated and a permanent rating is herein proposed.
History & Status:
Background: Pseudocercospora smilacicola 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 has previously been referred to as Ceracospora petersii and C. (or Pseudocercospora) mississippiensis, which are synonym species of Exosporium petersii which is morphologically distinguished from P. smilacicola (Braun et al., 2014; Farr & Rossman, 2016). However, Braun et al., (2014) reported that Pseudocercospora mississippiensis on Smilax riparia from Korea is morphologically indistinguishable from the Cuban and North American collections of P. smilacicola.
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. 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.
Hosts: Smilax auriculata (earleaf greenbrier), S. laurifolia (laurel greenbrier), S. pseudochina (bamboo vine), S. riparia, S. rotundifolia (roundleaf greenbrier), Smilax sp. (Braun et al., 2014).
Symptoms: Infected host plants exhibit leaf spots on both leaf surfaces and are sub-circular to angular or irregular, 1-10 mm in diameter, initially pale then turn dark brown and later develop a paler center, brownish to greyish brown, occasionally somewhat zonate with darker brown to black margin. Lesions or spots may be slightly raised and occasionally surrounded by a diffuse lighter halo (Braun et al., 2014).
Damage Potential: Specific losses due to Pseudocercospora smilacicola 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, Smilax californica and S. jamesii grow indigenously in the northern mountain and valley regions (Calflora, 2016). Smilax sp. vines and foliage are used in floral decorations and therefore, diseased plants could be of concern to greenbrier floral/ornamental production nurseries.
Worldwide Distribution: Asia: Japan, Korea; North America: USA, Cuba. (Braun et al., 2014). In the USA, Pseudocercospora smilacicola has been found in Georgia, Florida, Louisiana Mississippi, and Pennsylvania (Braun et al., 2014).
Official Control: None reported.
California Distribution: Pseudocercospora smilacicola has not been reported from California. The pathogen is not known to be established in California.
California Interceptions: Pseudocercospora smilacicola was detected shipments of Smilax sp. plants intercepted thrice from September 2015 to July 2016 (see ‘Initiating Event’).
The risk Pseudocercospora smilacicola 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): In California, host plants (Smilax spp.) grow indigenously in warm and humid conditions in northern mountain and valley regions. If introduced, the pathogen could establish in those limited areas.
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 for Pseudocercospora smilacicola is limited to Smilax spp.
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 smilacicola 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 Low (1): Infected host plants with leaf spot symptoms could lower value of nursery-produced Smilax plants used in floral/ornamental decorations.
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): Two plant species, namely, Smilax californica and S. jamesii, are native to California and grow under warm, humid conditions in northern mountain and valley regions of the State. The plants grow as under story plants in pine and mixed evergreen forest communities and provide food for wild animals and birds. Climate conditions may be conducive for the development of the pathogen if introduced. In severe infections, available food could be reduced for wildlife. Smilax jamesii is included in the California Native Plant Society Inventory of Rare and Endangered Plants on List 1B.3 7th/8th edition. Also, the pathogen could significantly impact nursery production of ornamental greenbrier foliage and vines.
Consequences of Introduction to California for Pseudocercospora smilacicola:
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 = 10
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): Pseudocercospora smilacicola is not established in California and has only detected in intercepted plant shipments to the State.
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
Conclusion and Rating Justification:
Based on the evidence provided above the proposed rating for Pseudocercospora smilacicola is B.
Agrios, G. N. 2005. Plant Pathology (Fifth Edition). Elsevier Academic Press, USA. 922 p.
Braun, U., Crous, P.W., and Nakashima, C. 2014. Cercosporoid fungi (Mycosphaerellaceae) 2. Species on monocots (Acoraceae to Xyridaceae, excluding Poaceae). IMA Fungus 5: 203-390.
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/
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/.
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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Pest Rating: B
Posted by ls