Stemphylium solani G. F. Weber 1930

California Pest Rating for

Stemphylium solani G. F. Weber 1930

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

On March 31, 2017, the CDFA Permits and Regulations Program requested a rating for Stemphylium solani. Therefore, the associated risk and current status of S. solani in California are assessed here and a permanent rating is proposed.

History & Status:

Background: Stemphylium solani is a fungal pathogen that causes Gray leaf spot disease in tomato, and Stemphylium leaf blight disease in cotton, garlic, and other hosts. Gray leaf spot in tomato is actually caused by three species of Stemphylium, one being S. solani and the other two species: S. lycopersici (Enjoji) W. Yaman (syn. S. floridanum Hannon & G. F. Weber) and S. botryosum Wallr. f. sp. lycopersici Rotem, Y. Cohen, & I. Wahl. Gray leaf spot is regarded one of the most destructive diseases of tomato in the southeastern United States and throughout the world wherever warm and humid conditions prevail (Jones & Pernezny, 2014).

Gray leaf spot disease has been reported from several countries worldwide including the United States (see ‘Worldwide Distribution’). In the United States, the disease was first observed in 1924 and by 1928 had spread throughout Florida causing widespread defoliation. Since then, the pathogen has been reported from several states but has never been reported from California.

Disease development: The disease begins in infested seedbeds and transplant houses or field-transplanted seedlings, usually when the plants are in the first true-leaf stage of growth. Cotyledons are not severely infected. The pathogen is spread when infected seedlings are transplanted to fields. Conidia (asexual spores) can be spread over extensive distances by wind. The teleomorph or sexual stage of S. solani is not known. The disease is favored by warm temperatures (24-27°C) and high humidity. Spore germination and infection of plant are dependent on the presence of free moisture (dew or rain) (Jones & Pernezny, 2014). Leaf wetness is considered more important than temperature in establishment of infection (Cerkauskas, 2005). Stemphylium solani survives as a saprophyte on infected plant debris or on volunteer tomato, pepper, gladiolus, blue lupine, and other wild solanaceous plants. In the southern state climates, the pathogen remains viable on tomato plants which are grown throughout the year (Jones & Pernezny, 2014). The pathogen can be seedborne (Koike et al., 2007).

Dispersal and spread: Infected plants, seedlings, and plant debris. Conidia may be wind-blown over extensive areas or by splashing water (Jones & Pernezny, 2014).

Hosts: Hosts of Stemphylium solani are included primarily in the plant family Solanaceae. Numerous other plant families are also included with their associated hosts, including Amaryllidaceae (Allium sp.), Asteraceae (Lactuca sp.), and Malvaceae (Gossypium hirsutum). Hosts include, Aegiceras corniculatum (black mangrove), Allium sativum (garlic), Aster sp. (aster), Basella rubra (Malabar spinach), Capsicum annuum (bell pepper), C. annuum var. annuum (cayenne pepper), C. frutescens (chili pepper), Carthamus sp. (distaff thistles), Cirsium sp. (thistle), Citrus sp. (citrus), Convolvulus arvensis (field bindweed), Cucumis sativus (cucumber), Dactylis glomerata (orchardgrass), Dianthus caryophyllus (carnation), Gossypium hirsutum (upland cotton), Ipomoea reptans (synonym: I. aquatica, swamp morning-glory), Kalanchoe blossfeldiana (flaming katy), Lactuca sativa (lettuce), Lupinus angustifolius (narrowleaf lupine), Lupinus sp. (lupine), Lycopersicon esculentum (synonym: L. lycopersicum, tomato), Lycopersicon sp., Pelargonium zonale (horse-shoe pelargonium), Physalis pubescens (husk tomato), Physalis sp. (groundcherry), Solanum gilo (gilo), S. lycocarpum (wolf apple), S. lycopersicum (garden tomato), S. melongena (aubergine/eggplant), S. melongena var. esculentum, S. pseudocapsicum (Jerusalem cherry), S. tuberosum (potato), Vicia faba (fava bean), Vigna sinensis (synonym: V. unguiculata, cowpea) (CABI, 2017; Farr & Rossman, 2017).

Symptoms: Gray leaf spots or lesions are almost entirely limited to the leaf blades, but under favorable conditions, lesions may develop on petioles and on the more tender parts of growing stems. Lesions on stems are linear and parallel to the stem. Fruit symptoms have not been observed. In infected tomatoes, symptoms of gray leaf spot are first exhibited as minute brownish-black specks on the lower leaves. Randomly scattered circular to oblong spots develop on adaxial and abaxial leaf surfaces without being restricted by leaf veins. The spots may be surrounded by a narrow yellow halo and enlarge to about 2.1 mm in diameter while individual spots on the base of leaves may enlarge to twice that size or more in diameter and occasionally coalesce, thereby, killing large portions of the leaf blade. As the spots enlarge, the centers turn gray, eventually dry, crack, and fall out. Frequently, at this stage entire leaves conspicuously turn yellow, especially if the infection is severe, and die rapidly, turning brown before dropping from the plants. Seedbed infections result in marked defoliation without conspicuous yellowing (Jones & Pernezny, 2014; Damicone & Brandenberger, 2015). In garlic, early symptoms of S. solani infection were observed as white spots (1-3 mm), which enlarged to sunken purple lesions, extending until the leaves withered (Zheng et al., 2008).

Damage Potential: Gray leaf spot almost entirely affects leaves, and defoliation can be severe reducing available photosynthetic areas of infected plants thereby, resulting in reductions in plant development, quality, and fruit yields. In China, garlic leaf blight caused by Stemphylium solani affected over 7,000 ha of field production and reduced yields up to 70% (Zheng et al., 2010). During 1994 and 1995, a severe epidemic of leaf blight of cotton in Brazil resulted in yield losses up to 100% in some commercial fields (Mehta, 1998). Gray leaf spot disease limited tomato production in Venezuela and Malaysia (Cadeño & Carrero, 1997; Nasehi et al., 2012). In California, processing tomatoes are grown in the warm and dry San Joaquin and Sacramento Valleys while fresh-market tomatoes are grown in the San Joaquin Valley, Central Valley, Central and Southern Coastal regions and the Imperial Valley. It is less likely that S. solani will be able establish under warm and dry regions of the state’s tomato production acreages, as well as under the possible use of resistant varieties, protectant fungicides and cultural management strategies. However, for tomato and other host plants under wet and warm climates, the pathogen may be able to establish within those regions.

Worldwide Distribution: Asia: Brunei Darussalam, China, Hong, Kong, Taiwan, Thailand, Korea, Malaysia; Africa: Libya, Mauritius, Senegal, Sudan, Tanzania; Europe: Greece, Spain; North America: Canada, USA (Alabama, Florida, Georgia, Indiana, Louisiana, Maryland, Mississippi, North Carolina, New Jersey, South Carolina, Tennessee, Texas, Virginia); South America: Brazil, Honduras, Venezuela; Central America and Caribbean: Cuba; Oceania: American Samoa (CABI, 2017; Cadeño & Carrero, 1997; Farr & Rossman, 2017).

Official Control: Presently, Stemphylium solani is on the Harmful Organisms list for Peru (USDA-PCIT, 2017).

California Distribution: Stemphylium solani has not been reported from California.

California Interceptions: None reported.

The risk Stemphylium solani would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Although Stemphylium solani has a wide host range that includes several economically important agricultural crops in California as well as wild solanaceous plants, the pathogen is dependent on leaf wetness for plant infection and additionally on warm temperatures for disease development. The disease is most severe under humid and overcast climate conditions that favor wet foliage mainly due to dew or rain. These conditions would allow the pathogen to establish in a larger but limited part 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: Stemphylium solani has a wide host range of plants included primarily in the family Solanaceae. However, numerous other plant families are also included with their associated hosts. Economically important crops include tomato, pepper, cotton, citrus, cucumber, lettuce, garlic, eggplant and others. Several wild solanaceous host plants could allow build-up of fungal inoculum.

Evaluate the host range of the pest.

Score: 3

– 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: Conidia are produced in abundance and readily dispersed by wind and splashing water. Also, the pathogen is spread through infected plants, seedlings, plant debris, and seed.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– 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: Stemphylium solani causes gray leaf spot in tomato and peppers as well as leaf blight in other hosts. Leaves are almost always entirely affected by the disease and defoliation can be severe reducing available photosynthetic areas of plants thereby, resulting in reductions in plant development, quality, and fruit yields. If not controlled, significant reductions in crop yield and markets could occur. Use of fungicides and cultural management practices could increase costs of crop production.

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

Economic Impact: A, 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 affect home/urban gardening of agricultural crops and ornamental hosts.

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 Stemphylium solani: High (13)

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’ in California.

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 = 13

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Stemphylium, solani is A.

References:

CABI, 2017. Stemphylium solani (gray leaf spot) basic datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/51531

Cerkauskas, R. 2005. Tomato diseases, Gray leaf spot, Stemphylium solani, S. lycopersici found worldwide in warm climates. AVRDC – The World Vegetable Center Fact Sheet. AVRDC Publication 05-634.

Cadeño, L., and C. Carrero. 1997. First report of tomato gray leaf spot caused by Stemphylium solani in the Andes Region of Venezuela. Plant Disease 81: 1332. http://dx.doi.org/10.1094/PDIS.1997.81.11.1332B

Damicone, J. P., and L. Brandenberger. 2015. Common diseases of tomatoes Part 1. Diseases caused by fungi. Oklahoma Cooperative Extension Service EPP-7625.

Farr, D. F., and A. Y. Rossman. 2017. Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved April 3, 2017, from http://nt.ars-grin.gov/fungaldatabases/

Jones, J. P., and K. L. Pernezny. 2014. Gray Leaf Spot. In Compendium of Tomato Disease and Pests Second Edition. Ed. J. B. Jones, T. A. Zitter, T. M. Momol, and S. A. Miller, APS Press. The American Phytopathological Society. 29-30 p.

Koike, S. T., P. Gladders, and A. O. Paulus. 2007. Stemphylium solani, S. lycopersici – gray leaf spot. In Vegetables diseases a color handbook. Academic Press, an imprint of Elsevier, Burlington, San Diego. 211-212 p.

Mehta, Y. R. 1998. Severe outbreak of Stemphylium leaf blight, a new disease of cotton in Brazil. Plant Disease, 82: 333-336.

Nasehi, A., J. B. Kadir, M. A. Zainal Abidin, M. Y. Wong, and F. Mahmodi. First report of tomato gray leaf spot disease caused by Stemphylium solani in Malaysia. Plant Disease 96: 1226. http://dx.doi.org/10.1094/PDIS-03-12-0223-PDN

USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. April 3, 2017, 1:17:10 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Zheng, L., J. B. HUANG, and T. HSIANG. 2008. First report of leaf blight of garlic (Allium sativum) caused by Stemphylium solani in China. Plant Pathology 57: 380.

Zheng, L., L. V. Rujing, J. Huang, D. Jiang, X. Liu, and T. Hsiang. 2010. Integrated control of garlic leaf blight caused by Stemphylium solani in China. Canadian Journal of Plant Pathology 32: 135-145.

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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