California Pest Rating for
Phakopsora phyllanthi Dietel 1910
Pest Rating: C
PEST RATING PROFILE
On December 4, 2015, a shipment of cut foliage of an unidentified plant species was intercepted at the USPS West Sacramento Distribution Center by the CDFA Dog Team. The shipment had originated in Florida and was destined to a private owner in Merced County, California. A sample of the symptomatic foliage was collected from the shipment and sent to the CDFA Plant Pathology Laboratory for pathogen diagnosis. On January 20, 2016, Suzanne Latham, CDFA plant pathologist, identified the rust fungal pathogen, Phakopsora phyllanthi associated with the diseased leaves and confirmed the identification by PCR sequencings. Subsequently, the shipment was destroyed (Martyn, 2016). On further investigation, USDA APHIS PPQ and Florida Department of Agriculture and Consumer Services communicated to Suzanne Latham, CDFA, that P. phyllanthi had been detected in three locations in Florida on February 18, 2016 (Latham, 2016). The risk of introduction and establishment of this pathogen in California is assessed and a permanent rating is proposed.
History & Status:
Background: Phakopsora phyllanthi is a fungal pathogen that causes rust disease in Phyllanthus spp. (‘gooseberry’). The pathogen has only been detected on certain species of the plant genus primarily grown in tropical and subtropical regions of the globe. In 2015, Phakopsora phyllanthi was first reported in the USA from Hawaii (Dietrich & Ko, 2015), and later in 2016, from Florida (Latham, 2016). The pathogen is not known to be present in California and was detected for the first time in an intercepted shipment of cut foliage from Florida, which was subsequently destroyed (see ‘Initiating Event’). The plant genus, Phyllanthus (Phyllanthaceae) contains several hundred species, however, only one species, P. caroliniensis subsp. caroliniensis (Carolina leaf-flower) native to the eastern United States, is known to be present in San Diego County as an introduced annual plant (Calflora, 2016).
Disease cycle: The life cycle of Phakopsora phyllanthi is not fully known. Teliospores (the sexual, overwintering stage of the fungus), have not been observed nor is it known if the pathogen needs an alternate host to complete its life cycle (Dietrich & Ko, 2015). It is likely, but not proven, that P. phyllanthi is spread to non-infected hosts via production of urediniospores only.
Dispersal and spread: Urediniospores are spread by wind and splashing rain. Insects, animals, and humans may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.
Hosts: Phyllanthus acidus (synonyms: Cicca acida, P. distichus; Tahitian gooseberry), P.benguetensis, P. emblica (Indian gooseberry), P. niruri (gale of the wind), P. phyllanthi, Phyllanthus sp. (Dietrich & Ko, 2015; Farr & Rossman, 2016). Some Phyllanthus species such as, P. emblica and P. acidus are cultivated for fruit in warm climates, while other species are pantropical weeds or grown for medicinal uses – but these species are not present in California.
Symptoms: Rust-infected Phyllanthus acidus (Tahitian gooseberry) trees may exhibit a general unthrifty appearance with thinning canopy, and barren branches or twigs. Leaves exhibit discolored chlorotic or necrotic spots on upper and lower surfaces. Small white-brownish raised spots or pustules containing numerous powdery urediniospores are produced on lower leaf surfaces. Affected leaves eventually drop off. Rust pustules and lesions are also formed on the surface of fruit (Dietrich & Ko, 2015).
Disease Potential: Phyllanthus species, such as P. acidua (Tahitian gooseberry) and P. emblica (Indian gooseberry) grown for their fruit in tropical climates, are not commercially cultivated in California, but are probably sold by rare fruit nurseries within the State. Infections of this rust pathogen could negatively impact production and value of plants. In general, severe infestation of rust can result in defoliation and reduction in plant growth, vigor and stand. Containment and management of the rust pathogen can be difficult as masses of air-borne spores produced can spread over long distances. Backyard growers, other small, rare fruit production growers, hobbyists, and rare plant nurseries in warm and wet climates of southern California may be at particular risk.
Worldwide Distribution: Asia: China, India, Indonesia, Malaysia, Philippines, Thailand; North America: USA (Florida, Hawaii); South America: Brazil, Ecuador, French Guyana, Venezuela (Dietrich & Ko, 2015; Farr & Rossman, 2016).
Official Control: None reported. Presently, Phakopsora phyllanthi has a temporary Q rating in California.
California Distribution: The gooseberry rust pathogen, Phakopsora phyllanthi is not established in California.
California Interceptions: The pathogen has only been detected once in a single intercepted quarantine shipment of unidentified cut foliage that originated in Florida (see “Initiating Event”).
The risk Phakopsora phyllanthi 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 Low (1): Phakopsora phyllanthi may establish in very limited areas within southern California that have warm and wet climates where the tropical host, Phyllanthus spp. is able to grow. Presently, only one species, Phyllanthus caroliniensis subsp. caroliniensis (Carolina leaf-flower) native to the eastern United States, is known to be present in San Diego County’s coastal region as an introduced annual plant.
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 the pathogen is very limited and comprises of some species non-native, tropical plants belonging to the genus Phyllanthus.
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): Phakopsora phyllanthi has high reproduction and dispersal potential. Spores are spread by wind and splashing rain. Insects, animals, and humans may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.
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): Reported hosts of the gooseberry rust pathogen are not to be present in California and therefore, no major economic impact of this pathogen is expect within California. However, if the pathogen was introduced, growers of rare, imported fruit plants, such as backyard growers, hobbyists, and rare plant nurseries in warm and wet climates of southern California may be at particular risk of reduced crop value. The economic impact is evaluated to be low.
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): Backyard growers, other small, rare fruit production growers, hobbyists, and rare plant nurseries in warm and wet climates of southern California may be at particular risk, if the pathogen were introduced into the State.
Consequences of Introduction to California for Myrtle Rust:
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 = 8 (Low).
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).
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 = 8.
Details of the pathogen’s complete life cycle including the need of an alternate host to complete its life cycle are not presently known. However, it is unlikely that this information will alter the proposed rating for the pathogen.
Conclusion and Rating Justification:
Based on the evidence provided above the proposed rating for gooseberry rust pathogen, Phakopsora phyllanthi is C.
Calflora. 2016. Calflora: Information on California plants for education, research and conservation [web application]. Berkeley, California: The Calflora Database [a non-profit organization]. http://www.calflora.org/
Dietrich, B., and M. Ko. 2015. Phyllanthus Rust Phakopsora phyllanthi Dietel. New Pest Advisory No. 15-02 October 2015, State of Hawaii Department of Agriculture.
Farr, D. F. and A. Y. Rossman. 2016. Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved October 17, 2016 from http://nt.ars-grin.gov/fungaldatabases/.
Khan, S. 2016. Email from K. Martyn, Yolo County, to S. Khan, CDFA, subject: “RE: Information request for A/Q/W reports”, dated February 11, 2016, forwarded to J. Chitambar, CDFA, by T. Walber, CDFA on October 18, 2016.
Latham, S. 2016. Email from S. Latham (CDFA) to J. Chitambar (CDFA), subject: “FW: confirmed ID: Positive for gooseberry rust (Phakopsora phyllanthi) from St. Petersburg, Pinellas Co., FL.”, sent October 17, 2016.
USDA-PCIT. 2016. United States Department of Agriculture, Phytosanitary Certificate Issuance & Tracking System (PCIT). https://pcit.aphis.usda.gov/PExD/faces/ViewPExD.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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Pest Rating: C
Posted by ls
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