California Pest Rating for
Diaporthe pseudophoenicicola R. R. Gomes, C. Glienke & Crous 2013
Pest Rating: C
PEST RATING PROFILE
On June 15, 2017, a shipment of an unknown plant, exhibiting symptoms of leaf spotting and destined to a commercial florist in Los Angeles County, was intercepted by the CDFA Dog Team in Los Angeles County. The shipment had originated in Kilgore, Texas. A sample of symptomatic leaves was submitted to the CDFA Plant Pathology Lab for disease diagnosis. On July 7, 2017, Suzanne Latham, CDFA plant pathologist, detected the fungal pathogen, Diaporthe pseudophoenicicola, in culture and confirmed its identity by PCR testing, as the cause for the disease. Later, on July 19, 2017, the same pathogen was detected in a date palm (Phoenix dactylifera) sample exhibiting decline and canker symptoms and collected from a tree located off Interstate 5 (I-5), in Orange County. The sample was collected by Orange County Agricultural officials and sent to the CDFA Plant Pathology Lab for diagnosis. Suzanne Latham detected D. pseudophoenicicola in culture and confirmed its identity by multi-locus sequencing. Later, the identity of the pathogen was also confirmed by the USDA APHIS Mycology and Nematology Genetic Diversity and Biology Laboratory at Beltsville, Maryland (Kennedy, 2017). The current status and rating of D. pseudophoenicicola in California is assessed here and a permanent rating is proposed.
History & Status:
Background: Diaporthe pseudophoenicicola is a fungal plant pathogen belonging to the order Diaporthales. The species was named after its morphological similarity to Diaporthe phoenicicola, which was originally isolated from dead leaves of Mangifera indica in Pakistan, however, later reported to differ morphologically from D. phoenicicola (Gomes et al., 2013). Diaporthe pseudophoenicicola is the sexual state of the pathogen, whereas, the asexual state belongs to the genus Phomopsis. Presently, D. pseudophoenicicola has only been reported from China, Iraq, and Spain (Farr & Rossman, 2017; Gomes, et al., 2013).
The asexual state of the fungal pathogen has been detected in California prior to the 2017 detection. In 2007, during a CDFA survey for palm wilt in Southern California, 16 detections were made of unidentified Phomopsis sp. on Phoenix canariensis, P. dactylifera, and P. reclinata in 10 counties. Only recently, was the Phomopsis species that was detected on P. dactylifera in Riverside County, identified through DNA sequencing as P. pseudophoenicicola (syn. Diaporthe pseudophoenicicola), thereby, indicating that this pathogen has already been established in California for at least 10 years. Complete identification of the remaining Phomopsis sp. is pending (personal communication: Suzanne Latham, CDFA).
Disease Development: While specific information is lacking, it is likely that plant infection and disease development caused by Diaporthe pseudophoenicicola are similar to those caused by other species of Diaporthe occurring as plant pathogens, endophytes or saprobes. The fungus produces ascospores (sexual spores) in perithecia (sexual fruiting bodies) and conidia (asexual spores) in pycnidia on dead twigs and leaves. Conidia are the main inoculum causing primary and secondary infections and are spread to host plants by splashing rains. Ascospores may be involved in long distance dispersal of the pathogen. The fungus is likely to overwinter as mycelium and/or as conidia within pycnidia (Agrios, 2005).
Dispersal and spread: Windblown/splashing rain and irrigation water, pruning tools, possibly insects, and animals can spread fungal spores to non-infected plants.
Hosts: Mangifera indica (mango), Phoenix dactylifera (date palm), P. canariensis (Canary Island palm) (Farr & Rossman, 2017; Gao et al., 2017; Gomes et al., 2013).
Symptoms: Diaporthe pseudophoenicicola causes symptoms of dieback and canker in infected mango and date palm. Dead tops of green leaves have been reported for date palms (Farr & Rossman, 2017; Gomes et al., 2013).
Damage Potential: Quantitative losses caused by Diaporthe pseudophoenicicola have not been reported. The pathogen causes dieback and cankers in mango and date palm. Therefore, if left uncontrolled, infections may result in reduced fruit and plant production and marketability. In California, nurseries and other growers of mango and date palms plants may be at risk of damage caused by this pathogen.
Worldwide Distribution: Asia: China, Iraq; Europe: Spain (Farr & Rossman, 2017; Gomes et al., 2013); North America: USA (California) (see: “Initiating Event”).
Official Control: No official control is reported for Diaporthe pseudophoenicicola or Diaporthe spp., however, Phomopsis spp. is presently on the ‘Harmful Organism List’ for French Polynesia (USDA PCIT, 2017). Currently, D. pseudophoenicicola has a temporary Q rating in California.
California Distribution: Los Angeles, Orange, and Riverside Counties.
California Interceptions: There has been only one interception. On July 7, 2017, Diaporthe pseudophoenicicola was detected in a shipment of an unknown plant that originated in Texas (see: ‘Initiating Event’).
The risk Diaporthe pseudophoenicicola would pose to California is evaluated below.
Consequences of Introduction:
1) Climate/Host Interaction: Mango and palm are the only known hosts and are grown in California. Diaporthe pseudophoenicicola may be able to infect its hosts under wet conditions and is therefore, only likely to establish in very limited regions of the State where mango and palm are grown mainly Southern California.
Evaluate if the pest would have suitable hosts and climate to establish in California.
– 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: The host range of the pathogen is presently limited to Mangifera indica and Phoenix dactylifera.
Evaluate the host range of the pest.
– 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: Diaporthe pseudophoenicicola has high reproductive potential with an abundant production of spores, however, the spores are dependent on splashing water for dispersal.
Evaluate the natural and artificial dispersal potential of the pest.
– 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: Quantitative losses caused by Diaporthe pseudophoenicicola have not been reported. Under favorable wet conditions for spread and disease development the pathogen may cause dieback and cankers in mango and palm. Therefore, if left uncontrolled, infections may result in reduced fruit and plant production and marketability. In California, nurseries and other growers of mango and date palms plants may be at risk of damage caused by this pathogen.,
Evaluate the economic impact of the pest to California using the criteria below.
Economic Impact: A, 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: 3
– 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.
5) Environmental Impact: The pathogen may impact palms used as ornamental plantings in commercial and private 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 Diaporthe pseudophoenicicola: 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 Low. The pathogen is already established in at least three counties in Southern California.
-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.
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
Identification of Phomopsis sp. (asexual state of Diaporthe) detected during the 2007 CDFA survey, is pending. Positive identification may provide new information on the distribution and hosts of D. pseudophoenicicola in California, while further stabilizing its currently proposed rating.
Conclusion and Rating Justification:
Based on the evidence provided above the proposed rating for Diaporthe pseudophoenicicola is C.
Agrios, G. N. 2005. Plant Pathology Fifth Edition. Elsevier Academic Press. 922 p.
Farr, D. F., and A. Y. Rossman. 2017. Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved September 20, 2017, from http://nt.ars-grin.gov/fungaldatabases/
Gao, Y., F. Liu, W. J. Duan, P. W. Crous, and L. Cai. 2017. Diaporthe is paraphyletic. IMA Fungus 8(1): 153-187.
Gomes, R.R., C. Glienke, S. I. R. Videira, L. Lombard, J. Z. Groenewald, and P. W. Crous. 2013. Diaporthe: a genus of endophytic, saprobic and plant pathogenic fungi. Persoonia 31: 1-41.
Kennedy, A. H. 2017. Email from A. H. Kennedy, Molecular Biologist, USDA APHIS Mycology and Nematology Genetic Diversity and Biology Laboratory, Beltsville, Maryland, to Suzanne Latham, Plant Pathologist, CDFA Plant Pest Diagnostics Branch, dated September 01, 2017, 5:14 am.
USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. Sept. 20, 2017, 2:11:43 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.
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