Diaporthe pseudomangiferae

California Pest Rating for

Diaporthe pseudomangiferae R. R. Gomes, C. Glienke & Crous

Pest Rating: C

PEST RATING PROFILE

Initiating Event:

On December 15, 2016, a shipment of Cacao seed pods with symptoms of necrotic spotting and rot and destined to a private citizen in Contra Costa County, was intercepted by the CDFA Dog Team at the United States Postal Service in Oakland, Alameda County. The shipment was confiscated and destroyed and a sample of symptomatic seed pods was sent to the CDFA Plant Diagnostics Branch for disease diagnosis. Suzanne Latham, CDFA plant pathologist identified the fungal pathogen, Diaporthe pseudomangiferae, as the cause for the disease and marked the first detection of D. pseudomangiferae in California. The current status and rating of D. pseudomangiferae in California is assessed and a permanent rating is proposed.

History & Status:

Background: Diaporthe pseudomangiferae is a fungal plant pathogen belonging to the order Diaporthales. The species was named after its morphological similarity to the Phomopsis mangiferae, which was originally isolated from dead leaves of Mangifera indica in Pakistan, however, later reported to differ morphologically from P. mangiferae (Gomes et al., 2013). Presently, D. pseudomangiferae has only been reported from the Dominican Republic, Puerto Rico, and Mexico (Farr & Rossman, 2017).

Diaporthe pseudomangiferae is not reported from the USA. The pathogen is not established in California but was detected in a mail shipment of Cacao seed pods which was intercepted in California and subsequently, confiscated, bagged, frozen, and disposed. However, its detection in Cacao marks a new host for the pathogen, which until now, has only been reported from mango (Gomes et al., 2013).

Disease development: While specific information is lacking, it is likely that plant infection and disease development caused by Diaporthe pseudomangiferae 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) (Farr & Rossman, 2017; Gomes et al., 2013; Serrato-Diaz et al., 2014); Cacao sp. (CDFA Pest and Damage Record, 2016).

Symptoms: In mango, Diaporthe pseudomangiferae causes inflorescence rot, rachis canker, and flower abortion. Symptoms are characterized by blackening of plant tissue with soft rot lesions and sunken lesions on the rachis respectively. In pathogenicity tests, initially white mycelia developed on inflorescences which later turned brown and flowers aborted (Serrato-Diaz et al., 2014).

Damage Potential: Quantitative losses caused by Diaporthe pseudomangiferae have not been reported. During a two-year disease survey in Puerto Rico, Serrato-Diaz et al., (2014) found 50% of mango symptomatic inflorescences to be infected with D. pseudomangiferae. The pathogen causes inflorescence rot, rachis canker, and flower abortion of mango. Therefore, if left uncontrolled, infections may result in reduced fruit production and marketability. In California, nurseries and other growers of mango plants may be at risk of damage caused by this pathogen.

Worldwide Distribution: Caribbean: Dominican Republic, Puerto Rico; North America: Mexico (Farr & Rossman, 2016; Gomes et al., 2013; Serrato-Diaz et al., 2014).

Official Control: None reported. In California, currently Diaporthe pseudomangiferae is a quarantine actionable pathogen with a temporary Q rating.

California Distribution: Diaporthe pseudomangiferae is not known to be established in California.

California Interceptions: There has been only one interception. On December 15, 2016, the fungal pathogen was detected in a shipment of Cacao seed pods that originated in Puerto Rico and was intercepted at a United States Postal Service in Alameda County (see: ‘Initiating Event’).

The risk Diaporthe pseudomangiferae would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Mango is the only known host in California. Diaporthe pseudomangiferae may be able to infect its host under wet conditions and is therefore, only likely to establish in very limited regions of the State where mango is grown mainly in the Coachella valley and foothill regions of southern California.

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: The host range of the pathogen is presently limited to Mangifera indica and Cacao

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: Diaporthe pseudomangiferae 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.

Score: 2

– 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: Under favorable wet conditions for spread and disease development, Diaporthe pseudomangiferae has been found to cause inflorescence rot, rachis canker, and aborted flowers in mango, thereby possibly resulting in lowered fruit production, value, and loss of markets.

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: Mango and cacao are the only known hosts, therefore no significant impact on the environment is expected.

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

Environmental Impact: None

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: 1

– 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 pseudomangiferae: Low (8)**

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’ (0).

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)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8.

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Diaporthe pseudomangiferae is C.

References:

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

Anon. 1996. Mango Mangifera indica L. California Rare Fruit Growers, Inc. http://www.crfg.org/pubs/ff/mango.html

Farr, D. F., and A. Y. Rossman. 2017. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved January 18, 2017, from http://nt.ars-grin.gov/fungaldatabases/

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.

Serrato-Diaz, L.M., L. I. Rivera-Vargas, and R. D. French-Monar. 2014. First report of Diaporthe pseudomangiferae causing inflorescence rot, rachis canker, and flower abortion of mango. Plant Disease 98(7): 1004

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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