Ascochyta aquilegiae (Rabenh.) Boerema, Fruyter & Noorder, 1997

California Pest Rating Proposal for
Ascochyta fungi (photo source: forestryimages.org)
Ascochyta fungi; Ascochyta spp. Lib.
Ascochyta aquilegiae (Rabenh.) Boerema, Fruyter & Noorder, 1997
Pest Rating:  C

 


PEST RATING PROFILE
Initiating Event:

On March 28, 2016, a sample of diseased Aquilegia sp. (columbine) plants showing symptoms of dieback, was voluntarily submitted by a nursery in Contra Costa County to the CDFA Plant Pathology Laboratory for disease diagnosis.  Suzanne Latham, CDFA plant pathologist, identified the associated fungus plant pathogen, Ascochyta aquilegiae, as the cause for the disease.  The pathogen was assigned a temporary “Z” rating as it has been reported earlier in California and is considered widely distributed.  That rating is reassessed here and a permanent rating is proposed.

History & Status:

BackgroundAscochyta aquilegiae causes dark leaf spots, stem lesions, and crown rots in plants belonging to the family Ranunculaceae, including several species in the genera Aquilegia and Delphinium.  The fungal species has undergone several name changes in fungal taxonomy and is known by several synonyms including, Stagonosporopsis aquilegiae, Actinonema aquilegiae, Ascochyta laskarisii, Diplodina delphinii, Phoma aquilegiicola, Phyllosticta aquilegiae, and Phyllosticta aquilegicola (Farr & Rossman, 2016).

Disease development and spreadAscochyta aquilegiae attack primarily plant leaves by means of spores (conidia) and, following infection, produce numerous condia that are spread to other plants by wind, wind-blown rain, water, and insects.  Conditions that favor prolonged leaf-wetness in warm climates often favor development of the pathogen. The pathogen is also transmitted to non-infected sites through the movement of infected plant materials and debris. The fungus overwinters primarily in fallen leaves or infected leaf debris, or as mycelium in infected tissues of perennial plants (Agrios, 2005; Pscheidt & Ocamb, 2016a, 2016b).

Hosts: Aquilegia spp. (columbine), Aconitum spp. (aconite/wolf’s bane), Clematis sp. (clematis), Consolida spp. (larkspur), Coptis chinensis (goldthread), Delphinium spp. (delphinium/larkspur) (Farr & Rossman, 2016; French, 1989; Garibaldi et al., 2011; Yu et al., 2014).

Symptoms and damage potential: Ascochyta aquilegiae causes leaf spots, stem cankers and crown rots.  Leaf lesions of infected Aquilegia and Coptis plants are extensive, usually beginning at the leaf margin and extending to the central leaf blade eventually coalescing to cover entire leaf, irregular, brown to black, necrotic, slightly sunken with a well-defined border and surrounded by a violet-brown halo.   As the disease progresses, stems are also affected causing death of the apical part of the plant (Garibaldi et al., 2011; Yu et al., 2014). In Delphinium spp., petioles develop brown water-soaked lesions near the base of succulent plants.  Less vigorous plants show black local lesions on the petiole.  Inflorescences and seed pods develop a blackish decay.  Generally, crown rot may be found in plants two years or older (Pscheidt & Ocamb, 2016a, 2016b).  Small, dark brown to black fungal fruiting bodies (pycnidia) may be present in the lesions.

Damage Potential:  While information on the economic importance of the disease caused by Ascochyta aquilegiae is limited, the development of leaf spots, stem cankers and crown rots in infected plants may result in reduced plant production, yield, and marketability of columbine and other host plants used in residential gardens and commercial landscapes.  Plants are particularly at risk of pathogen infection in warm and moist natural climates of California, and in nursery-controlled productions.  In China, A. aquilegiae caused yield losses of 15-75% in gold thread, an important herbaceous plant used in traditional Chinese medicine (Yu et al., 2014).

Worldwide Distribution:  Asia:  Armenia, China, Japan, Russia; Africa: South Africa, Zimbabwe, Europe: Bulgaria, Czechoslovakia, Germany, Italy, Netherlands, Poland, Scotland, United Kingdom; North America: Canada, USA; Oceania: New Zealand.  It is widespread within the USA in Alaska, California, Connecticut, Iowa, Idaho, Maryland, New Jersey, New York, Oregon, Pennsylvania, Texas, Washington, Wisconsin (Farr & Rossman, 2016; Garibaldi et al., 2011; Pscheidt & Ocamb, 2016a, 2016b; Yu et al., 2014).

Official Control: None reported. Currently, the pathogen has a temporary ‘Z’ rating in California, which indicates that it is a previously unrated organism of known economic and/or environmental detriment but generally distributed in the state.

California Distribution: Ascochyta aquilegiae has been detected in California’s northern and southern coastal counties which include: Del Norte, Humboldt, Mendocino, Sonoma, Marin, San Francisco, San Mateo, Santa Cruz, Alameda, Santa Clara, San Benito, Monterey, San Luis Obispo, Santa Barbara, Ventura, Los Angeles, Orange, and San Diego Counties (French, 1989).

California Interceptions: None reported.

The risk Ascochyta aquilegiae 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): Conditions that favor prolonged leaf-wetness in warm climates often favor development of Ascochyta aquilegiae.  The pathogen is already known to be present in northern and southern coastal counties in California.

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): Presently, the host range is limited to few species within Ranunculaceae. 

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 Medium (2): Ascochyta aquilegiae produces numerous condia the infect plants, however, to spread to other plants, they are dependent on wind, wind-blown rain, water, and insects.  Furthermore, prolonged leaf-wetness in warm climates is needed to favor development of the pathogen in plants. The pathogen is also transmitted to non-infected sites through the movement of infected plant materials and debris.

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): While information on the economic importance of the disease caused by Ascochyta aquilegiae is limited, the development of leaf spots, stem cankers and crown rots in infected plants may result in reduced plant production value and marketability of columbine and other host plants used in residential gardens and commercial landscapes.  Plants are particularly at risk of pathogen infection in warm and moist natural climates of California, and in nursery-controlled productions

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): Commercial landscape and home garden plantings could be negatively impacted if infected by Ascochyta aquilegiae under favorable moist climate conditions.  The pathogen could directly affect certain species of larkspur, namely, Delphinium bakeri (Baker’s larkspur), D. hesperium ssp. cuyamacae (Cuyanaca larkspur), D. luteum (golden larkspur), and D. variegatum ssp. kinkiense (San Clemente Island larkspur) included in the ‘State and Federally Listed Endangered, Threatened, and Rare Plants of California, July 2015’ thereby, potentially lowering biodiversity, natural communities or ecosystem processes.

Consequences of Introduction to California for Ascochyta aquilegiae:

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 Medium (-2): Presently, Ascochyta aquilegiae is known to be present in northern and southern coastal counties in California.

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:   

The impact and spread of this pathogen to other intrastate regions where host species are grown, is not known.  Future reports of the detection of P. digitalidis in California could lower the overall score for the pathogen although it is unlikely to affect its final rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Ascochyta aquilegiae is C.

References:

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

Farr, D.F., & Rossman, A.Y. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved April 18, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Garibaldi, A., D. Bertetti, M. T. Amatulli, and M. L. Gullino.  2011.  First report of leaf spot of fan columbine (Aquilegia flabellata) caused by Phoma aquilegiicola in Italy.  Plant Disease 95:880.  http://dx.doi.org/10.1094/PDIS-05-10-0391.

Pscheidt, J.W., and Ocamb, C.M.  2016a. Columbine (Aquilegia spp.) leaf spots.  Pacific Northwest Plant Disease Management Handbook. © Oregon State University. pnwhandbooks.org/plantdisease/node/3020. http://pnwhandbooks.org/plantdisease/columbine-aquile.

Pscheidt, J.W., and Ocamb, C.M.  2016b. Delphinium – leaf spot and crown rot.  Pacific Northwest Plant Disease Management Handbook. © Oregon State University. pnwhandbooks.org/plantdisease/node/3118.  http://pnwhandbooks.org/plantdisease/delphinium-leaf-spot-and-crown-rot.

Yu, Y., Z. C. Su, W. Z. Tan, and C. W. Bi.  2014.  First report of a leaf spot on goldthread (Coptis chinensis) caused by Phoma aquilegiicola in China. Plant Disease 98:1428. http://dx.doi.org/10.1094/PDIS-01-14-0010-PDN.


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.


Comment Period:  CLOSED

The 45-day comment period opened on May 10, 2016 and closed on Jun 24, 2016.


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Pest Rating:  C


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