Septoria protearum Viljoen & Crous 1998

California Pest Rating for

Septoria protearum Viljoen & Crous 1998

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

On March 29, 2017, lavender (Lavendula sp.) plants showing symptoms of leaf spots were detected in a nursery in San Luis Obispo County by County Agricultural officials. A sample of diseased leaves was sent to the CDFA Plant Pathology Laboratory for diagnosis. On May 8, 2017, Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Septoria protearum associated with the diseased leaf tissue. The pathogen was assigned a temporary Q rating. Subsequently, the consequences of introduction and establishment of S. protearum in California are assessed and a permanent rating is proposed herein.

History & Status:

Background: Septoria protearum is a fungal pathogen that causes leaf spot disease in host plants. Septoria protearum is the asexual (anamorph) stage, for which the sexual stage or teleomorph is not known. Verkley et al., (2013) included the pathogen S. pistaciae as a synonym of S. protearum since it could not be robustly distinguished based on a seven-gene phylogenetic analysis. Crous et al., (2013) stated that further study and inoculation trials are needed to confirm synonymy of the two species. Also based on DNA evidence, Verkley et al., (2013) reported multiple host family associations for S. protearum, which is unusual for other species of the genus. Farr & Rossman (2017) included hosts of S. protearum in genera belonging to nine families. The current CDFA detection of the pathogen in lavender, increases the number of represented families to ten. Septoria pistaciae (syn. S. protearum according to Verkley et al., 2013) was previously reported from a pistachio orchard in California (Farr et al., 1989; Michailides, 2005).

Disease development: While there is no specific information on the disease development of Septoria protearum (Michailides, 2005), it is likely to be similar to that of other species in the genus. Generally, Septoria spp. overwinter as mycelium and as conidia (asexual spores) within pycnidia (asexual fruiting structures) on or in seed and on diseased plant debris left in the field. Infected seeds produce infected seedlings that may result in damping-off or provide inoculum for subsequent infections. When pycnidia in infected plant debris become wet, they swell and conidia are exuded in long tendrils and thereafter, spread by splashing rain, irrigation water, as well as contaminated tools and animals. Septoria species usually require high moisture for infection and severe disease development, however, they can cause disease under a wide range of temperatures (10-27°C) (Agrios, 2005). The teleomorph (sexual) stage of S. protearum is unknown.

Dispersal and spread: Infected plants and nursery stock, splashing rain, irrigation water, plant leaf debris, contact with cultivation tools and animals (Agrios, 2005).

Hosts: Presently, all reported hosts of Septoria protearum are included in several families, viz. Aspleniaceae, Proteaceae, Rutaceae, Rosaceae, Oleaceae, Boraginaceae, Davalliaceae, Anacardiaceae, Aracaceae, and Lamiaceae. Hosts include: Asplenium ruta-muraria (walrue fern), Boronia denticulata (mauve Boronia), Gerbera jamesonii (Gerber daisy), Geum sp. (Geum), Gevuina avellana (Avellano/Chilean hazelnut), Hedera helix (common ivy/English ivy), Ligustrum vulgare (common privet/ European privet), Masdevallia sp. (Masdevallia), Myosotis sp. (mouse’s ear), Nephrolepis sp. (fern), Pistacia vera (pistachio), Protea cynaroides (king protea), Protea sp. (protea), Skimmia sp. (Skimmia), Zantesdeschia aethiopica (calla lily) (Crous et al., 2008; Farr & Rossman, 2017; Verkley et al., 2013). In addition, the pathogen was recently detected in Lavendula sp. (lavender; Lamiaceae) (see: ‘Initiating Event’).

Symptoms: Leaf spots are produced in plants infected by Septoria species. Leaf spots usually start on the lower leaves and progress upwards, initiating as small yellowish specks that later enlarge, turn pale brown or yellowish gray, and finally dark brown. They are usually surrounded by a narrow yellow region and may be circular to irregular. Affected leaves may turn yellow and eventually die. Numerous small black pycnidia are aggregated and appear as dots within the leaf spots (Agrios, 2005). In pistachio, Septoria protearum produces numerous, subcuticular brown spots, 0.5-1.5 mm on both sides of the leaf, with numerous black pycnidia clustered within the spots. In California, in pistachio fruit, the pathogen causes distinct grayish to light-brown fruit lesions, 1-4 mm in diameter, surrounded by a bright, distinctly reddish halo and usually located near the peduncle. Leaf infections have not been observed (Michailides, 2005).

Damage Potential: Quantitative losses due to Septoria protearum have not been reported. Photosynthetic area can be reduced due to leaf spotting. In severe infections, leaf wilt, premature leaf drop, and reduced tree vigor may result. Leaf and fruit spots are produced in pistachio. Leaf spot damage caused by S. protearum may significantly impact production and marketing of nursery ornamental plants.

Worldwide Distribution: Africa: South Africa; Europe: France, Germany, Italy, Netherlands, Spain, Canary Islands; North America: USA (California); Oceania: New Zealand (Farr & Rossman, 2017).

Official Control: No official control for Septoria protearum has been reported. However, currently Septoria spp. is on the ‘Harmful Organism’ list for the Bolivarian Republic of Venezuela (USDA-PCIT, 2017).

California Distribution: Previous to its current detection, Septoria protearum was reported from a pistachio orchard in California. Its recent detection was in a nursery in San Luis Obispo County (see “Initiating Event’).

California Interceptions: None.

The risk Septoria protearum would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Septoria protearum has a diverse range of hosts which largely include several ornamental plant species. While the pathogen may be able to cause disease under cool and warm temperatures, it is dependent on high moisture for infection and severe disease development. Therefore, it is likely that the pathogen may be able to establish in a larger but limited area of California.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– 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: Presently, the pathogen has a moderate and diverse range of hosts inclusive of species in ten plant families.

Evaluate the host range of the pest.

Score: 2

– 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: Septoria protearum has high reproductive potential however, dispersal of conidia from pycnidia are dependent on wet conditions from splashing rain, dew, and irrigation water. Further artificial spread is caused by use of contaminated tools, animals, etc. Therefore, a ‘Medium’ rating is given to this category.

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: Septoria protearum causes leaf and fruit spot in host plants. In California, it has been found in pistachio. Other hosts include several nursery-grown ornamental plant species. While there is no information on quantitative crop loss caused by this pathogen, leaf spot disease could lower crop value and cause loss of markets. Use of preventive chemical sprays and other control measures could increase production costs. Avoidance of overhead irrigations would require changes in cultural practices of irrigating plants.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: B, C, D

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 could significantly impact ornamental plantings in home/ urban, public gardens and other recreational 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 Septoria protearum: Medium (11)

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 was originally recorded in one pistachio orchard in California (county unknown) and since then has also been found in a nursery in San Luis Obispo. It is therefore, considered to have a localized distribution within the State.

Score: -1

-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 = 10

Uncertainty:

Distribution of Septoria protearum in California is not fully known. Treatments with suppressive fungicides may have kept its spread in check. Also, a need for further research on taxonomic studies of the species has been mentioned in published literature. This information, when available, may alter the proposed rating for this pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Septoria protearum is B.

References:

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

Crous, P. W., B. A. Summerell, L. Mostert, and J. Z. Groenewald. 2008. Host specificity and speciation of Mycosphaerella and Teratosphaeria species associated with leaf spots of Proteaceae. Persoonia 20: 59-86.

Farr, D. F., and A. Y. Rossman. 2017. Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved May 12, 2017, from http://nt.ars-grin.gov/fungaldatabases/

Farr, D. F., G. F. Bills, G. P. Chamuris, and A. Y. Rossman. 1989. Fungi on Plants and Plant Products in the United States. APS Press. St. Paul, Minnesota.

Michailides, T. J. 2005. Pest, disease, and physiological disorders management: above ground fungal diseases. In: Pistachio Production Manual, Eds. Beede, R. H., M. W. Freeman, D. R. Haviland, B. A. Holtz, and C. E. Kallsen, Davis, CA. Fruit and Nut Research and Information Center, Department of Plant Sciences, University of California Davis. 214–232 pp.

USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. May 12, 2017, 1:43:31 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Verkley, G. J. M., W. Quaedvlieg, H. D. Shin, and P. W. Crous. 2013. A new approach to species delimitation in Septoria. Studies in Mycology 75: 213-305.

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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