Tag Archives: plant pathogen

Fungi, Plant Pathogens

Puccinia crepidis-japonicae (Lindr.) Dietel (Rust)

California Pest Rating for
Puccinia crepidis-japonicae (Lindr.) Dietel
(Rust)
Pest Rating: D 
PEST RATING PROFILE
Initiating Event:

Recently, the USDA NPAG (New Pest Advisory Group) reported and evaluated the detection of Puccinia crepidis-japonicae in Gainesville, Florida, thereby, marking the first record of this pathogen in the USA.  Subsequently, the risk and consequences of its introduction to, and establishment in California is assessed here and a permanent rating is proposed.

History & Status:

Background:  In February 2015, the fungal rust pathogen, Puccinia crepidis-japonicae, was discovered on the exotic weed Youngia japonica (oriental false Hawksbeard) in Florida (USDA NPAG, 2015).  The pathogen primarily attacks weed plants.  While P. crepidis-japonicae is reported to attack plant genus Prenanthes, the host Y. japonica was originally described under the genus name Prenanthes japonica. Therefore, it is likely that the pathogen may be limited to the host belonging to Youngia spp.  This common host, Youngia spp., is present in southern California, and Y. japonica grows there as a garden weed at the edge of lawns and planting beds.

Puccinia crepidis-japonicae has not been reported from California. However, there is a very early record of a different species belonging to the same group, namely, P. crepidis-acuminatae P. Syd. & Syd., which was detected on naked-stem Hawksbeard, (Crepis runcinata which is now a synonym of Youngia runcinata) and tapertip Hawksbeard (Crepis acuminata, synonym of Y. acuminata) in California (Blasdale, W. C. 1919: A preliminary list of the Uredinales of California. University of California Publications in Botany, 7:101-157).

Puccinia crepidis-japonicae is not considered an economically damaging pathogen as it is associated with non-economically important plants. Pereira et al., 2002 suggested that P. crepidis-japonicae may play a significant role as a biocontrol agent against its weed host.  In Florida, the possibility of using this exotic rust against the exotic host, Youngia japonica, is being considered (USDA NPAG, 2015).  However, it is not known if the pathogen kills its host since it needs the latter in order to live as a parasite.

Disease cycle:  The complete life cycle and climate requirements for disease development for Puccinia crepidis-japonicae are not known.  In general, rust pathogens require living host plants to complete a life cycle.  The life cycle may be completed in one or two hosts – and this is not known for P. crepidis-japonicae. Rusts attack only certain genera or varieties of plants.  This appears to be the case for P. crepidis-japonicae. Rusts may have a short cycle (microcyclic) producing only two different spores: teliospores and basidiospores, or a long cycle (macrocyclic) producing five different spores: teliospores, basidiospores, spermatia, aeciospores, and urediniospores. Only urediniospores and teliospores are reported for P. crepidis-japonicae, so this pathogen may be macrocyclic. Urediniospores infect host plants and can rapidly spread to cause new and multiple infections of host plants (Agrios, 2005).

Dispersal and spread:  The pathogen is spread from plant to plant mainly by windblown spores.  Urediniospores can be transported over several hundred kilometers by strong winds and washed down by rain to available hosts.  Insects, animals, humans, and rain may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.

Hosts: Asteraceae – Prenanthes sp. (rattlesnake root), Youngia fusca, Y. japonica (oriental false Hawksbeard), Y. tenuifolia, Y. japonica (originally cited as Crepis japonica which is now a synonym of Y. japonica) (Farr & Rossman, 2015).

Symptoms and damage potential:  Puccinia crepidis-japonicae primarily attacks weed plants (e.g., Youngia japonica) producing dark brown, irregularly oval-shaped leaf lesions containing urediniospores (Pereira et al., 2002).

Worldwide Distribution: Asia: China, Korea, Japan, Yoron Islands; North America: United States; Oceania: Australia, New Caledonia; South America: Brazil (Farr & Rossman, 2015; USDA NPAG, 2015; Pereira, et al., 2002; Zhuang, 1989).

In the United States, it has only been reported from Florida (USDA NPAG, 2015).

Official Control: Puccinia crepidis-japonicae is not listed as a harmful organism by any country (PCIT, 2015).  No official control of this pathogen is reported.

California Distribution: Puccinia crepidis-japonicae is not present in California.

California Interceptions:  None reported.

The risk Puccinia crepidis-japonicae Rust 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 Low (1):  If introduced, Puccinia crepidis-japonicae is likely to establish under favorable environmental conditions in limited areas within southern California where its common host, Youngia spp. is present.

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): The host range is limited to weed plants in the genus Youngia spp. in the family Asteraceae. 

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 High (3): Puccinia crepidis-japonicae has both high reproduction and dispersal potential through the production of abundant, infective urediniospores and the ease of their spread by winds, insects, animals, humans, and rain to non-infected host plants.  

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 Low (1): Puccinia crepidis-japonicae is not considered an economically damaging pathogen as it is associated with non-economically important plants or weeds.

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 Low (1): None.

Consequences of Introduction to California for Puccinia crepidis-japonicae Rust:

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 = 7

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: Not established (0).

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 = 7.

Uncertainty:

Details of the life cycle and complete host range are unknown.  However, it is unlikely this knowledge will significantly alter the proposed rating for Puccinia crepidis-japonicae.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Puccinia crepidis-japonicae Rust is D.

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 August 31, 2015, from http://nt.ars-grin.gov/fungaldatabases/

Pereira, O. L., J. R. P. Cavallazzi and R. W. Barreto.  2002.  First report of Uredo crepidis-japonicae and Septoria crepidis on Crepis japonica in Brazil. Fitopathológicas Brasileira 27 (3):319.

USDA NPAG.  2015.  NPAG report Puccinia crepidis-japonicae (Lindr.) Dietel: Rust.  USDA/APHIS/ PPQ/CPHST/PERAL NPAG Report 20150615.docx. 6 pg.

Zhuang, J. Y. 1989. Rust fungi from the desert of northern Xinjiang. Acta Mycologica Sinica 8(4):259-269.

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.

Pest Rating: D

Posted by ls

Fungi, Plant Pathogens

Colletotrichum asianum Prihastuti, L. Cai & K. D. Hyde, 2009

California Pest Rating for
Colletotrichum asianum Prihastuti, L. Cai & K. D. Hyde, 2009
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

During July, 2014, mango fruit exhibiting spots or lesions were intercepted by the CDFA Dog Team in Santa Clara County and samples of symptomatic fruit were sent to the CDFA Plant Pathology Laboratory for diagnosis.  The associated anthracnose fungal pathogen, Colletotrichum asianum, was identified by Suzanne Latham, CDFA plant pathologist and later confirmed by USDA.  Subsequently, the fruit was destroyed and the shipment was traced back by the USDA to Florida and C. asianum was detected in fruit still on the tree.  This detection marked the first report of the pathogen in the USA (USDA, 2015).  Since its first detection and during April and June 2015, C. asianum continued to be detected in mango fruit shipments destined for Alameda, Butte, Los Angeles, Merced, Riverside, Sacramento, San Joaquin, and Santa Clara Counties.  The shipments were intercepted at USPS distribution facilities by Dog Teams.   On July 7, 2015, C. asianum was found to be associated with necrotic spots in mango leaves of plants in a nursery in Imperial County.  This was the first detection of the pathogen from leaves. In all cases of interceptions mentioned afore, subsequent to the detection of C. asianum, all fruit and plant shipments were received from Florida and either destroyed or rejected from entering California.  Currently, C. asianum has a temporary ‘Q’ rating.  The risk of introduction and establishment of this pathogen in California is assessed and a permanent rating is proposed herein.            

History & Status:

Background:  Colletotrichum asianum was first reported to be associated with coffee berries (Coffea arabica) in northern Thailand (Prihastuti et al., 2009).  The pathogen is a distinct fungus species belonging to the vastly morphological and physiological variable C. gloeosporioides complex and is generally identified from other species of the complex only with DNA sequences (Prihastuti et al., 2009; Weir et al, 2012).

Hosts: Mangifera indica (mango) and Coffea arabica (coffee) (Prihastuti et al., 2009; Weir et al., 21012).

Symptoms:  Initially, small, dark brown circular spots are produced on mango fruit and leaves infected with Colletotrichum asianum.  These spots increase rapidly in size and coalesce to form dark depressed anthracnose lesions in ripened fruit (Krishnapillai & Wilson Wijeratnam, 2014). Generally, Colletotrichum-infected host plants exhibit symptoms of anthracnose which include dark brown leaf, stem and fruit spots and wilting of leaves which often result in dieback and reduction in plant quality.

Damage Potential:  Anthracnose disease caused by Colletotrichum asianum can result in reduced plant quality and growth, fruit production and marketability.  Estimates of yield/crop loss due to this pathogen have not been reported.  Nursery production of potted host plants or in greenhouses are particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  In cultivated fields, disease development may be sporadic as it is affected by levels of pathogen inoculum and environmental conditions.

Disease Cycle:  It is likely that Colletotrichum asianum has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on plant residue in soil, on infected plants, and on seeds.  During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers.   Conidia are transmitted to host plants.  Humid, wet, rainy weather is necessary for infection to occur.  These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem under controlled environments of greenhouses.  Conidia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue.

Transmission:  Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution:  Africa: South Africa; Asia: Japan, Sri Lanka, Thailand, Philippines; South America: Brazil, Colombia, Panama; Australia; North America: Florida (Farr & Rossman, 2015; Krishnapillai & Wilson Wijeratnam, 2014; Lima et al., 2013; Prihastuti et al., 2009; Sharma et al., 2013; USDA, 2015; Vieira et al., 2014; Weir et al., 2012).

Official Control:  In California C. asianum is an actionable, Q-rated pathogen, and infected plant material is subject to destruction or rejection.

California Distribution: Colletotrichum asianum is not established in California (see “Initiating Event”).

California Interceptions:  During 2015, Colletotrichum asianum has been intercepted several times mainly in shipments of mango fruit and less frequently in mango plants (leaves) that originated in Florida (see ‘Initiating event’).

The risk Colletotrichum asianum 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) – Similar to other species of Colletotrichum, C. asianum requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement may limit the ability of the pathogen to fully establish and spread under dry field conditions in California. Also limiting is the very narrow host range of C. asianum comprising mango and coffee.  Coffee is not cultivated in California and mango has limited production in the foothills of southern California or warm locations in the Coachella Valley.  It is also grown in residential backyards and few nurseries, either as fruit or nursery stock.  The pathogen could establish within these limited regions under conducive climates.

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) – The host range of Colletotrichum asianum is limited to mango and coffee.

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 High (3) – The pathogen has high reproductive potential and conidia are produced successively.  They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

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 High (3) – Mango fruit production, in particular, can be limited by its susceptibility to anthracnose under wet conditions. Therefore, under suitable climates, the pathogen could lower plant growth, fruit production and value and trigger the loss of markets.

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 Medium (2) – The pathogen could significantly impact cultural practices or home garden plantings.

Consequences of Introduction to California for Colletotrichum asianum:

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 of Colletotrichum karstii to California = (11).

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 not established (0).  Colletotrichum asianum is not established in California.  All instances of interception of C. asianum-infected mango fruit and plants were either rejected or destroyed. 

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 = 11.

Uncertainty:

Periodic surveys need to be conducted to confirm the presence/absence of C. asianum in commercial and private production regions within California.  Subsequent results may alter the herein proposed rating for the pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum asianum is B.

References:

CABI.  2015.  Colletotrichum asianum basic datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/

Farr, D. F., & A. Y. Rossman.  Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 7, 2015, from

http://nt.ars-grin.gov/fungaldatabases/

Kitterly, W. R., and A. P. Keinath.  1996.  Fungal disease of aerial parts: Anthracnose. In ‘Compendium of Cucurbit Diseases’.  Edited by T. A. Zitter, D. L. Hopkins, and C. E. Thomas, APS Press The American Phytopathological Society Minnesota, USA, p. 24-25.

Krishnapillai, N., and R. S. Wilson Wijeratnam.  2014.  First report of Colletotrichum asianum causing anthracnose on Willard mangoes in Sri Lanka.  New Disease Reports, 29:1. http://dx.doi.org/10.5197/j.2044-0588.2014.029.001 .

Lima, N. B., M. V. de A. Batista, MAde Morais Júnior, M. A. G. Barbosa, S. J. Michereff, K. D. Hyde, M. P. S. Câmara.  2013. Five Colletotrichum species are responsible for mango anthracnose in northeastern Brazil. Fungal Diversity, 61:75-88. http://rd.springer.com/article/10.1007/s13225-013-0237-6.

Prihastuti, H., L. Cai, H. Chen, E. H. C. McKenzie, and K. D. Hyde.  2009. Characterization of Colletotrichum species associated with coffee berries in northern Thailand. Fungal Diversity 39: 89-109.

Sharma, G., M. Gryzenhout, K. D. Hyde, A. K. Pinnaka, and B. D. Shenoy.  2015.  First report of Colletotrichum asianum causing mango anthracnose in South Africa.  Plant Disease, 99:725.  http://dx.doi.org/10.1094/PDIS-08-13-0837-PDN .

USDA. 2015.  Email from John H. Bower, USDA ,APHIS, PPQ, PHP to Nick Condos, CDFA, subject: Colletotrichum asianum on mango from CA and from the source tree in FL (first records for Continental US), dated April 30, 2015 6:26 am.

Vieira, W. A. S., S. J. Michereff, M. A. de Morais Jr., K. D. Hyde, and M. P. S. Câmara.  2014.  Endophytic species of Colletotrichum associated with mango in northeastern Brazil.  Fungal diversity, 67:181-202.

Weir, B. S., P. R. Johnston, and U. Damm.  2012.  The Colletotrichum gloeosporioides species complex.  Studies in Mycology, 73:115-180. DOI:10.3114/sim0011.

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.

PEST RATING:  B

Posted by ls 

Bacteria, Plant Pathogens

Xanthomonas arboricola pv. pruni (Smith) Vauterin, Hoste, Kersters & Swings

California Pest Rating for
Xanthomonas arboricola pv. pruni (Smith) Vauterin, Hoste, Kersters & Swings
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

In September 2013, CDFA plant pathologist, Luci Kumagai, identified Xanthomonas arboricola pv. pruni associated with symptomatic almond seedlings that were submitted by Sierra Gold Nursery in Sutter County to the CDFA Plant Pathology Laboratory.  David Marion, CDFA environmental scientist, surveyed the nursery shade house where the trees were housed and determined that only Monterey Almond trees exhibited symptoms of bacterial canker.  Subsequently, in line with CDFA’s current Q rating of X. arboricola pv. pruni and ‘Nursery Standard of Cleanliness’, the lot of affected almond trees was destroyed and other Prunus spp. in the nursery were protected from further potential infection. Near about that time, the pathogen was found in commercial almond orchards in a few counties in northern California, thereby marking its first non-official detection in the State.  The detection of the associated disease was reported by the University of California Cooperative Extension Farm Advisor for Stanislaus County.  In view of the recent finds, the current temporary rating is herein assessed for the proposal of a permanent rating.

History & Status:

Background:  Xanthomonas arboricola pv. pruni is a bacterial pathogen that attacks only Prunus spp. causing disease commonly known by various names: bacterial canker of stone fruit, bacterial leaf spot of stone fruit, bacterial shot-hole of stone fruit, and black spot of stone fruit.  The bacterium belongs to the family Xanthomonadaceae of the order Xanthomonodales.  No strains have been reported, however, difference in virulence to peach, plum and apricot have been noted (Du Plessis, 1988).  The species was first described in North America (Michigan) in 1903 on Japanese plum, but it not clear if it spread from there throughout the world or if it naturally has a wide geographical range.  In California, it is a relatively new disease of almonds (UCIPM, 2013).

Disease cycle:  On Prunus species, the pathogen overwinters in plant tissues such as buds, protected areas (cracks in the bark), and in leaf scars. On almonds it overwinters on fruit mummies and twig cankers.  On plum and apricot, cankers formed during the preceding season continue to develop in spring and provide a source of inoculum.  During late winter as temperatures warm, peach leaf and flower buds swell, and as new tissue growth initiates, bacteria multiply and cause the epidermis to rupture, forming a lesion or spring canker.  Bacteria are spread from cankers or mummified fruit to newly emerging leaves by dripping dew and splashing and/or wind-blown rain.  Infection takes place through natural openings or wounds.  High moisture conditions favor leaf and fruit infections.  Severe infection is favored by warm temperatures (19-28°C), light frequent rainfall and fairly heavy winds and dew.  Following foliar infection, cankers develop in the green shoot tissue, but usually become sealed off by formation of a periderm barrier layer.  Also, cankers tend to dry out during the summer months thereby reducing viability of bacteria.  For that reason, twig cankers produced in plum and peach during the summer are not considered important overwintering sites or sources of inoculum for spring infections.  Generally, late shoot infections that occur just before leaf fall in autumn provide the primary inoculum source for the following spring (CABI, 2014; UCIPM, 2013).

Hosts:  Xanthomonas arboricola pv. pruni attacks only Prunus species, in particular fruit crops such as almonds, peaches, cherries, plums, apricots, P. salicina (Chinese/Japanese plum), and ornamental species of Prunus including P. davidiana (Chinese wild peach), Japanese apricot (P. mume), and P. laurocerasus (cherry laurel).  Generally, species of the Sino-Japanese group (P. japonica and P. salicina) are more susceptible than European plums (CABI, 2014; EPPO, 2013)

Symptoms: Symptoms may vary depending on the infected plant host and plant part.

On peach leaves, infection is first apparent on the lower leaf surface as small, pale green to yellow, circular or irregular areas with a light tan center. These spots become apparent on the upper surface as they enlarge, becoming angular and darken to deep-purple, brown or black.  Tissue immediately surrounding the diseased spots becomes yellow.  The spots may darken before they drop out giving a shot-hole appearance. Usually, spots are concentrated toward the leaf tip as bacteria accumulate in that area with droplets of rain or dew. Bacterial ooze may exude from the spots.  In severe infections defoliation may occur.  On peach fruit, small, sunken circular spots with frequently water-soaked margins or light green halos appear on the surface. Pitting and cracking occur near the spots as the fruit enlarges.  Gum may exude from bacterial wounds, especially after heavy rains.  Spring cankers appear on the top part of overwintering twigs before green shoots are produced.  These cankers initiate as small, water-soaked slightly darkened superficial blisters that extend 1-10 cm along the length of the twig or girdle it causing tip death or “black tip injury’.  The area below the dead tip harbors the bacteria.  Twigs that get infected late in season result in ‘summer cankers’ which are dark purple spots surrounding lenticels that later dry out and become limited, dark, sunken, circular to elliptical lesions.

On plum leaves: the shot-hole effect is more pronounced than on peach leaves.  On plum fruit symptoms vary from large sunken, black lesions to small pit-like lesions.  On plum and apricot, twig cankers are perennial developing on 2-3 year old twigs.  As a result, deep-seated cankers are formed in the inner bark thereby deforming and killing twigs.

On cherry leaves symptoms develop similar to peach but are rarely of importance.  Fruit may be distorted and bacteria usually internally inhabit fruit pulp.

On almond:  In California, damage has been predominant on the ‘Fritz’ variety however similar damage has been observed by researchers on ‘Monterey’, ‘Padre’, and ‘Nonpareil’ varieties (Holtz et al., 2013).  Symptoms on leaves, twigs and fruit are similar to those produced on peach.  Symptoms on infected almond nuts include the production of amber colored gum from spots on the hull which internally reveals a lesion. Lesions may enlarge, become sunken and orange in color, or exude an orange slime.  Furthermore, infected nuts may stick on spurs and be close to mummified, lesion nuts of the previous year.    Leaves may have spots, turn yellow and drop prematurely.  Twigs may have lesions or cankers.

Damage Potential:  The pathogen is capable of causing severe defoliation thereby weakening trees.  The leader (i.e., the vertical stem at the top of the trunk) dies and fruit is reduced in size and often not marketable.  Serious losses in peach (25-75%), plum and apricot production are reported from Australia, New Zealand, and the USA (CABI, 2014; EPPO, 2014).  Damage to stone fruit is more severe where the latter are grown in light, sandy soils than in heavier soils (UCIPM, 2013).

Transmission:  Local spread of the bacterial pathogen from cankers and mummified fruit is limited and dependent on dripping dew and splashing and/or wind-blown rain.  Long distance spread, as in international trade, is through infected plantings, budwood, and fruit (except seeds).

Worldwide Distribution: Asia (China, India, Iran, Japan, Korea DPR, Korea Republic, Lebanon, Pakistan, Saudi Arabia, Taiwan, Tajikistan); Africa (South Africa, Zimbabwe); Europe (Bulgaria, France, Italy, Moldova, Montenegro, Netherlands, Romania, Russia (Far East, Southern), Slovenia, Spain, Switzerland, Ukraine); North America (Bermuda, Canada, Mexico, USA); South America (Argentina, Brazil, Uruguay); Oceania (Australia, New Zealand).

In the USA it is present in Alabama, Arkansas, California, Connecticut, Florida, Georgia, Idaho, Kentucky, Louisiana, Maryland, Michigan, Mississippi, Missouri, New Jersey, New York, North Carolina, Oregon, Pennsylvania, South Carolina, and Texas.

Official Control: Ten countries list X. arboricola pv. pruni on their “Harmful Organism Lists’ namely, Canada, Chile, Ecuador, Israel, Madagascar, Mexico, Morocco, New Caledonia, Peru, and Turkey.  Whereas, 41 countries worldwide list X. campestris pv. pruni (synonym of X. arboricola pv. pruni) on their lists (USDA PCIT, 2014).  Xathomonas arboricola pv. pruni is listed as an A2 quarantine pest by EPPO and of little economic importance in EPPO countries where it is present.  Also, it is of quarantine significance for the Inter-African Phytosanitary Council/IAPSC (EPPO, 2014).

California Distribution:  The bacterial spot pathogen is relatively in California.  It has been found on almonds (mainly Fritz cultivar), in Colusa, Merced, Stanislaus, and San Joaquin Counties, as well as sweet cherry and other stone fruit crops in San Joaquin and Stanislaus Counties (UCIPM, 2013).

California Interceptions:  The pathogen was recently intercepted in a nursery in Sutter County.  The plants were destroyed (see ‘Initiating event’.)

The risk Xanthomonas arboricola pv. pruni 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 High (2):   The pathogen is limited to high moisture and warm temperature conditions and regions for establishment.

2)  Known Pest Host Range: 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.

Risk is Medium (2): The host range is limited to Prunus spp. stonefruit which is cultivated in vast acreage within California.  

3)  Pest Dispersal Potential: Evaluate the 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.

Risk is High (2): The pathogen increases and tends to cause infections in spring and its spread to non-infected tissue is dependent on warm temperatures and wet conditions brought about by wind-driven rainfall, water-splash and dripping dew.

4)  Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

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 High (3): Infection of Prunus spp. could lower crop yield and value thereby resulting in a loss of market.

5)  Environmental Impact: Evaluate the environmental impact of the pest on California using these criteria:

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:

– 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): Infection of ornamental Prunus species, in particular could impact residential and commercial cultivation of ornamental and fruit trees, requiring cultural practices to remove infected plant parts and mummified fruit.  In addition, official and private treatment programs may be needed to manage the pathogen.

Consequences of Introduction to California for Xanthomonas arboricola pv. pruni:

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 = 12

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 Low (-1):  Xanthomonas arboricola pv. pruni has been detected on almond, sweet cherry and other stone fruit in four counties within the Central Valley of 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 = 11

Uncertainty:

To date, Xanthomonas arboricola pv. pruni has been detected mainly in almond orchards in four California counties.   Targeted surveys for the detection of this relatively new pathogen may result in a wider distribution and range of host plants than currently known for the State.  If that occurs, then a lower rating than that proposed here is probable.  Therefore, diligent screenings and management of planting stock in nurseries will remain critical to mitigate risk of introduction of the pathogen to new, non-infected commercial production sites.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Xanthomonas arboricola pv. pruni is B.

References:

CABI.  2014.  Xanthomonas arboricola pv. pruni datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/

Du Plessis, H. 1988.  Differential virulence of Xanthomonas campestris pv. pruni for peach, plum, and apricot cultivars.  Phytopathology, 78 (10):1312-1315.

EPPO, 2014.  Xanthomonas arboricola pv. pruni (XANTPR).  PQR database.  Paris, France:  European and Mediterranean Plant Protection Organization.  http://newpqr.eppo.int

Holtz, B., D. Doll, R. Duncan, J. Edstrom, T. Michailides, and J. Adaskaveg.  2013.   http://www.ipm.ucdavis.edu/PDF/MISC/168605.pdf

UCIPM.  2013.  Bacterial spot (Xanthomonas arboricola pv. pruni) University of California Agriculture & Natural Resources, UC IPM Online, Statewide Integrated Pest Management Program.  http://www.ipm.ucdavis.edu/EXOTIC/bacterialspot.html

USDA PCIT.  2014.  USDA Phytosanitary Certificate Issuance and Tracking System.  Phytosanitary Export Database.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp

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.

PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Tranzschelia mexicana M. Scholler & M. Abbasi

California Pest Rating for
Tranzschelia mexicana M. Scholler & M. Abbasi
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

During April, 2015, Heather Scheck, plant pathologist, Santa Barbara County Agricultural Commissioner’s office detected symptoms of rust on capulin cherry nursery stock growing in a nursery in Santa Barbara County.  Cheryl Blomquist, CDFA plant pathologist, examined infected leaf samples and identified the associated rust pathogen Tranzschelia mexicana.  This pathogen was first found in Santa Barbara in 2014 in 4 year old cherry trees grown in a residential backyard garden.

History & Status:

Background:  Tranzschelia mexicana is a fungal pathogen that causes rust in capulin cherry trees.  The pathogen was originally described from Mexico and thus named to indicate its natural distribution in southern Mexico.  It is assumed that this pathogen requires two different kinds of hosts to complete its life cycle (also called a host alternating rust) and is macrocyclic (i.e., produces urediniospores, teliospores and basidiospores on main host and spermatia and aeciospores on an alternate host).  However, the alternate host as well as spermogonia and aecia (fruiting structures producing spermatia and aeciospores respectively) are unknown for T. mexicana. Furthermore, Blomquist et al. (2015) did not detect telia in rust-infected capulin cherry leaves that were collected from trees in Santa Barbara County, California, during October and November 2014 and January 2015 and thereby, deduced that the fungal species does not form telia.  This is not unusual for host alternating rusts when aecial hosts (alternate hosts) are not present in regions. Scholler et al., suggest that Anemone mexicana – a plant native to the Valley of Mexico – might be the aecial host for the capulin rust pathogen.  Nevertheless, it is likely that T. mexicana has spread without its aecial host via production of urediniospores only (Scholler et al., 2014).

Hosts: Capulin/Mexican black cherry, (Prunus salicifolia, Rosaceae) is the only reported host for Tranzschelia mexicana (Scholler et al., 2014; Blomquist et al., 2015).

Symptoms: Tranzschelia mexicana causes yellow spots on the upper side of leaves and brownish pustules on the underside.  Entire infected trees are susceptible to high infestations although fewer pustules may be present in younger leaves than older leaves.  Severe infestations may cause defoliation and reduced plant stands (Blomquist et al., 2015).

Damage Potential:  Capulin cherry is not a commercially cultivated crop in California, however, a small percentage of nursery stock plants are sold in the retail market.  Infections of this rust pathogen could negatively impact production and value of plants in private residences, public parks, amusement parks, and other environments. Rusted capulin cherry leaves are not only aesthetically unsightly but also negatively impact plant growth.  Severe infestations of rust can result in defoliation and reduction in plant growth, vigor and stand.  Containment and management of the rust pathogen can be difficult as infected leaves produce masses of air-borne spores enabling long-range spread and infection.

Transmission:  The pathogen is spread from plant to plant mainly by windblown spores.  Urediniospores can be transported over several hundred kilometers by strong winds and washed down by rain to available hosts.  Insects, animals, humans, and rain may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.

Worldwide Distribution: North America: Mexico, USA (California – CDFA pest detection records); South America: Colombia, Ecuador (Scholler et al., 2014). It is assumed that the distribution of the capulin rust pathogen extends beyond the above mentioned distribution in the Americas where capulin cherry is cultivated.

Official Control: None reported.

California Distribution:  Capulin rust pathogen, Tranzschelia mexicana, has been detected in residential backyard and nursery environments in Santa Barbara County (see ‘Initiating Event’).

California Interceptions:  There have been no quarantine interceptions of Tranzschelia mexicana was intercepted in California.

The risk Tranzschelia mexicana 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 High (3) – Tranzschelia mexicana is able to establish wherever capulin cherry trees are grown in California.  Capulin cherry (Prunus salicifolia) is a rare fruit and is grown in many low chill regions in California for its flowers and edible fruit.

2)  Known Pest Host Range: 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.

Risk is Low (1) – Currently the host range of Tranzschelia mexicana is limited to capulin cherry (Prunus salicifolia). The alternate host for this pathogen is not known. Blomquist et al (2015) did not find symptoms of rust on several peaches, apricots and other Prunus spp. that were growing on the same property with rust-infested capulin cherry trees.

3)  Pest Dispersal Potential: Evaluate the 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.

Risk is High (3) – The infective spores of Tranzschelia mexicana namely, urediniospores, are produced in abundance and are spread to healthy plants mainly by wind. Insects, animals, humans, rain, and infected nursery plants also aid in its spread.

4)  Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

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 High (3) – Severe infestations of the capulin cherry rust pathogen could result in defoliation and reduction of plant growth, vigor and stand, and loss of markets. Nursery plantings are at risk being significantly impacted by the introduction of this pathogen. Without eradicative action subsequent to detection of bamboo rust-infected plants within greenhouse environments, there is the risk of further spread to the outside environment. The spread of the rust pathogen would be difficult to manage due to its effective means of windblown transmission.

5)  Environmental Impact: Evaluate the environmental impact of the pest on California using these criteria:

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:

– 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) – Capulin cherry plantings for aesthetic and rare fruit production value by private growers may be impacted by the capulin cherry rust pathogen subsequently triggering additional treatment programs.

Consequences of Introduction to California for Tranzschelia mexicana

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 of Tranzschelia mexicana to California = (13).

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.

Evaluationis Low (-1): Presently, Tranzschelia mexicana is only established in Santa Barbara, 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 = 12

Uncertainty:

Future detection surveys for Tranzschelia mexicana in nurseries and established capulin cherry plantings are needed to gain further information of the probable introduction, establishment and distribution of this pathogen in California.  This information could alter the proposed rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Tranzschelia mexicana is B.

References:

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

Blomquist, C. L., M. Scholler and H. J. Scheck.  2015.  Detection of rust caused by Tranzschelia mexicana on Prunus salicifolia in the United States.  Plant Disease (Accepted for publication).

California Rare Fruit Growers, Inc.  1997. Capulin cherry Prunus salicifolia HBK. Fruit Facts. http://www.crfg.org/pubs/ff/capulin-cherry.html .

Scholler, M., M. Abbasi and F. Friedrich.  2014.  Tranzschelia in the Americas revisited: two new species and noted on the Tranzschelia thalictri complex.  Mycologia, 106: 448-455. DOI: 10.3852/12-260.

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.

PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Podosphaera caricae-papayae

California Pest Rating for
Podosphaera caricae-papayae
Pest Rating: B
PEST RATING PROFILE
Initiating Event: 

In March 2014, Podosphaera caricae-papayae, a powdery mildew fungal pathogen, was identified by morphological and sequence analyses by Suzanne Latham, plant pathologist, CDFA. The symptomatic papaya leaf sample was collected from an ornamental container nursery in Santa Barbara County by County Agricultural plant pathologist, Heather Scheck. The identity of the pathogen was confirmed by USDA APHIS PPQ Mycologist, Megan Romberg.  Subsequently, the nursery destroyed the infected papaya plants.  In May 2014, the same pathogen was detected on papaya plants, grown in a commercial papaya fruit production nursery greenhouse at a different location within Santa Barbara County.  The detection of powdery mildew of papaya in Santa Barbara County marks a first record for North America.  Initially, the fungal pathogen was assigned a Q rating which is reassessed herein for the proposal of a permanent rating.

History & Status:

Background:    Podosphaera caricae-papayae was originally described by Tanda and Braun in 1985 as Sphaerotheca caricae-papayae.  However, in 2000 the species was placed in the genus Podosphaera based on molecular sequence analysis by Braun and Takamatsu (Romberg, 2014).  Complications in taxonomic classification of the species exist over the accurate linkage of the sexual or teleomorph stage to the asexual or anamorph stage of the pathogen and further molecular and morphological studies are needed to determine the correct taxonomic position of P. caricae-papayae.  In the original description of the species, the teleomorph stage, Sphaerotheca, was linked to the anamorph stage, Oidium caricae (Liberato et al., 2004).  However, later this linkage was proven inaccurate and O. caricae was rejected as the anamorph stage, thereby leaving the classification of an asexual stage for P. caricae-papayae unresolved.  The exact distribution is unknown because it is unclear which records of “O. caricae” actually belong to P. caricae-papayae.  In 2012, P. caricae-papayae was synonymized with the morphologically similar species P. xanthii – the pathogen causing powdery mildew on cucurbits (Braun & Cook, 2012).  The synonymy of P. xanthii and P. caricae-papayae is in question given recent molecular work (Takamatsu et al., 2010).  P. caricae-papayae is only known from infected seedlings of papaya in Australia, China, India, Japan, New Zealand and California (USA).  Greenhouse infections of papaya plants in California were reported as being caused by “cucurbit powdery mildew”.  Infections of mature papaya plants in the field have never been reported.

The infected papaya plants recently detected in California only bear the anamorph stage which morphologically resembles the anamorph stage of P. caricae-papayae that was described by Tanda and Braun in 1985 (Romberg, 2014).  Furthermore, molecular sequence analysis revealed that the sequences from both California detections are identical to a sequence of P. caricae-papayae from Thailand that was used by Takamatsu et al., (2010) in their phylogenetic analyses of the genus Podosphaera (Latham, 2014; Romberg, 2014).  Unfortunately, no morphological information of the Thailand isolate is available to compare with the California isolate.  The sequence from Thailand is the only P. caricae-papayae sequence deposited in GenBank and therefore, analytical sequence comparisons of isolates of P. caricae-papayae from California and Thailand with those from other reported regions are lacking.  Nevertheless, the Thailand sequence is different from other Podosphaera species sequences in Genbank, including the cucurbit powdery mildew, P. xanthii.   Further molecular and morphological studies which would include more isolates will help determine the correct taxonomic position of P. caricae-papayae within the genus Podosphaera in the family Erysiphaceae of the order Erysiphales (Takamatsu et al., 2010).

Powdery mildew of papaya is on obligate parasite.  The fungus grows on the surface of plant tissue and invades by sending feeding organs (haustoria) into the plants epidermal cells only in order to obtain nutrients.  Mycelium produces conidiophores on the plant surface.  Each conidiophore produces chains of conidia (spores) that are dispersed by air currents.  Powdery mildew thrives in warm and humid environments. Low light levels, high humidity, moderate temperature and rainfall enhance disease development in papaya (Cunningham & Nelson, 2012). Generally, disease can be severe in warm and dry climate as long as the relative humidity is high enough to enable condial germination and infection.

Hosts: Carica papaya (papaya).

Symptoms:  Powdery mildew infects papaya plants of all ages however seedlings in greenhouses are more susceptible than field grown plants.  The pathogen frequently infects young immature leaves, petioles, pedicels, peduncles, and unripe fruit. Early on, the undersides of leaves become speckled with small water-soaked spots with white to grayish powdery fungal patches usually near the leaf veins.  Yellow-green spots develop on the corresponding upper sides.  Soon the patches grow in size and coalesce, and fungal growth may grow on the upper leaf surface and veins.  In severe infections, leaves become necrotic, curl and drop prematurely.  Mildew patches also develop on immature fruit and can cover the entire fruit, eventually resulting in deformed fruit (Cunningham & Nelson, 2012).

Damage Potential:  Infections can result in prematurely defoliated trees, mildewed and deformed fruit causing significant if not, total losses in plant growth and crop yield.   Deformed fruit is not marketable resulting in lowered sales.  Infections occurring in plants grown in greenhouse can result in severe spread and loss in production if left unmanaged.

In California, there is no commercial acreage under cultivation for papaya. Production is limited to ornamental and fruit production nursery greenhouse and residential gardens for ornamental purposes in southern California counties.  Under those environments, loss in production is possible if not managed.

Transmission:  Conidia (spores) are primarily dispersed by wind currents.

Survival:  During cool weather, condia production ceases and powdery mildew fungi overwinter as cleistothecia (a sexually produced, closed, fruiting body) and mycelium in dormant plant tissue. However, only the asexual stage has been found in California greenhouses.  Constant greenhouse growth conditions could perpetuate the anamorphic stage of the fungus.

Worldwide Distribution: The true distribution of the California isolate of P. caricae-papayae is currently not known.  Molecular sequence analyses remain unknown for reported isolates of P. caricae-papayae from Australia, China, India, Japan, and New Zealand.  The sequence of the isolate from Thailand is the only one deposited in GenBank, and is identical to the sequence of the California isolate.

Official Control:  There is no record of official control against this pathogen.

California Distribution: The pathogen has only been detected in greenhouses of two nurseries at two different locations in Santa Barbara County.

California Interceptions:  There are no records of Podosphaera caricae-papayae having been intercepted in papaya imported to California.

The risk Podosphaera caricae-papayae 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 Low (1) – Of what is currently known, Podosphaera caricae-papayae will only infect papaya and therefore, is limited to wherever papaya is cultivated.  In California, where there is no major cultivation of papaya, plants are propagated in greenhouses for fruit production and ornamental plantings in residential and urban environments of southern counties.  As evident in the recent detection in Santa Barbara, the pathogen is capable of establishing in nursery grown papaya.  

2)  Known Pest Host Range: 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

Risk is Low (1) – The host range is limited to Carica papaya (papaya).

3)  Pest Dispersal Potential: Evaluate the 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

Risk is High (3) – Under suitable climate conditions, airborne conidia are produced in abundance and readily spread by wind currents to non-infected sites.  Within and outside greenhouse environments, the pathogen is capable of rapidly spreading to non infested papaya plants as well as other sites where papaya is grown.

4)  Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

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 High (3) – The pathogen can potentially cause significant losses in plant growth and crop yield. Powdery mildew infections of papaya fruit could lower crop yield and value causing significant losses in production.  This would result in loss of markets, and change in cultivation practices to prevent the spread of inocula to non-infected, healthy plants.

5)  Environmental Impact: Evaluate the environmental impact of the pest on California using these criteria:

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:

– 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) – Although limited to papaya, occurrence of the pathogen in nursery and outside environments could significantly impact home/urban gardening and/or ornamental plantings, as well as result in the imposition of additional official or private treatments to mitigate effects of infection.

Consequences of Introduction to California for Podosphaera caricae-papayae:

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 of P. caricae-papayae to California = (11).

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 Low (-1).  The pathogen was only detected within nursery greenhouses in Santa Barbara, California.  Measures were taken to destroy infested plants.

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:

To date, the detection of P. caricae-papayae in California is limited to two in-greenhouse sites in Santa Barbara County.  There have not been any additional detections, surveys or reports of new infestations in papaya production nurseries and/or outside environments to provide further knowledge of the presence of this pathogen. Further comparative molecular analyses against reported international isolates of the pathogen may provide information of its global distribution and clarity of its taxonomic classification, however, it’s separation from P. xanthii (present in California) has already been proven (see ‘Background’).

While the host range and distribution of the pathogen within California is currently known to be limited, the potential of incurring significant damage due to infection by P. caricae-papayae places the limited distribution of instate papaya nursery ornamental and production plants at medium risk and, therefore, warrants assignment of a B rating.  Future detections of P. caricae-papayae could indicate a wider distribution than presently known and result in a lower rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Podosphaera caricae-papayae is B.

References:

Braun, U. and R. T. A. Cook.  2012.  Taxonomic manual of the Erysiphales (Powdery Mildews).  Centraalbureau voor Schimmelcultures, vol. 11, 707 p.

Cunningham, B and S. Nelson.  2012.  Powdery mildew of Papaya in Hawai’i.  College of Tropical Agriculture and Human Resources University of Hawai’I at Mānoa.  Plant disease, PD-90.

Latham, S.  2014.  Email to John Chitambar, CDFA: sent July 3, 2014.

Liberato, J. R., R. W. Barreto and R. P. Louro.  2004. Streptopodium caricae sp. nov., with a discussion of powdery mildews on papaya, and emended descriptions of the genius Streptopodium and Oidium caricae.  Mycological Research 108:1185-1194.

Romberg, M. K.  2014.  Email from M. K. Romberg, APHIS-USDA, to Suzanne Latham, CDFA: sent March 26, 2014.

Takamatsu, S., S. Ninomi, M. Harada and M. Havrylenko.  2010.  Molecular phylogenetic analyses reveal a close evolutionary relationship between Podosphaera (Erysiphales: Erysiphaceae) and its rosaceous hosts.  Persoonia, 24, 38-48.

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.

PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Colletotrichum boninense Moriwaki, Toy. Sato & Tsukib. 2003

California Pest Rating for
Colletotrichum boninense Moriwaki, Toy. Sato & Tsukib. 2003
Pest Rating: B
PEST RATING PROFILE
Initiating Event:  

During February 2015, the fungal pathogen Colletotrichum boninense was detected in infected Aglaonema commutatum (Aglaonema/Chinese evergreen) cuttings in a nursery in Vista, San Diego County, California.  The plants were part of an incoming nursery shipment from Fallbrook, San Diego County, California and originated in a nursery in Costa Rica. A month later, the pathogen was detected twice in San Diego in two different shipments of Aglaonema sp. plants: one sent to the Vista nursery by the same shipper as before, and the other sent by a different shipper to a different nursery.  The latter two shipments had also originated in Costa Rica.  The pathogen was cultured from leaf spots, sequenced, and identified by Suzanne Latham, CDFA plant pathologist.  This detection was considered a new US record and reportable by the USDA. The species identity was confirmed by the USDA PPQ National Mycology Laboratory.  Consequently, the shipment of plants was destroyed.   A permanent rating for Colletotrichum boninense is proposed herein.        

History & Status:

Background:  Colletotrichum boninense was first discovered associated with Crinum asiaticum var. sinicum (Amaryllidaceae) in the Bonin Islands, Japan (Moriwaki et al., 2003).  These scientists also found the species in Japan to be associated with several other hosts plants of different plant families.  Furthermore, C. boninense was originally described in 2003 as a segregate of the vastly morphological and physiological variable C. gloeosporioides complex (CABI, 2014; Morikwaki et al., 2003).  Prior to its segregation as a species, isolates of C. boninense were often identified as C. gloeosporioides.  However, after the segregation, researchers found that C. boninense actually comprised of a complex of several species and by 2012, through molecular phylogenetic analyses of 86 strains of C. boninense, Damm et al. (2012) were able to recognize 18 species within the C. boninense complex including C. boninense in its strict sense (s. str.) based on DNA sequence data and morphology.  The current proposed rating is for C. boninense s. str.

Hosts: Host plants of C. boninense s. str. are very diverse and include members in the plant families Amaryllidaceae, Bignoniaceae, Podocarpaceae, Proteaceae, Solanaceae and Theaceae (Damm et al., 2012).  The CDFA 2015 detection of C. boninense s. str. on Aglaonema commutatum would also include the family Araceae.

The range of host plants for Colletotrichum boninense s. str. is not well understood from reports published prior to 2012 as many of those reports refer to the broad C. boninense complex (sensu lato).  Subsequently, those reported hosts would need to be molecularly verified to be C. boninense s. str.  and include members of the genera Bletilla, Camellia, Capsicum, Cattleya, Clivia, Coffeae, Crinum, Cucumis, Cymbidium, Dacyrarpus, dendrobium, Dracaena, Eucalyptus, Hippaestrum, Leucospermum, Oncidium, Pachira, Panax, Passiflora, Pleione, Protea, Prunus, and Solanum (Farr & Rossman, 2015).

Symptoms:  Colletotrichum-infected host plants exhibit symptoms of anthracnose which include dark brown leaf, stem and fruit spots and wilting of leaves often resulting in dieback and reduction in plant quality.

Damage Potential:  Anthracnose disease caused by Colletotrichum boninense can result in reduced plant quality and growth.  Estimates of yield/crop loss due to this pathogen have not been reported.  Nursery production of potted host plants or in greenhouses are particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  In cultivated fields, disease development may be sporadic as it is affected by levels of pathogen inoculum and environmental conditions.

Disease Cycle:  It is likely that Colletotrichum boninense has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on plant residue in soil, on infected plants, and on seeds.  During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers.   Conidia are transmitted to host plants.  Humid, wet, rainy weather is necessary for infection to occur.  These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem under controlled environments of greenhouses.  Condia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue.

Transmission:  Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution:  Australia, Brazil, China, Colombia, Japan, Korea, the Netherlands, New Zealand, South Africa, and Zimbabwe (Farr & Rossman, 2015).

Except for Japan, Australia, and New Zealand where the presence of Colletotrichum boninense s. str. was verified (Damm et al., 2012), reports from other countries should be independently verified for C. boninense s. str.

The 2010 report of Colletotrichum boninense in Florida, USA, reported by Tarnowski & Ploetz,  is now not considered to be C. boninense s. str. but actually a different species within the C. boninense species complex (personal communication: Aaron Kennedy, National Identification Services, USDA-APHIS-PPQ-PM). The Florida report was published before the C. boninense complex was split into several species in 2012.

Official Control:  Colletotrichum boninense is considered a new USA record and reportable to the USDA.

California Distribution: There is no official record of the establishment of Colletotrichum boninense in California however during the early 1980s, CDFA plant pathologists identified C. gloeosporioides in Camelia japonica (Theaceae) and other hosts in the plant family Araceae which are included as host for C. boninense s. str.  These detections were made in northern and southern coastal counties.  At that time specific molecular diagnostic tests were not available to enable the distinction of C. boninense.  It is, therefore, possible that these detections may have included C. boninense s. str. (Suzanne Latham and Cheryl Blomquist, CDFA, personal communication).  No eliminative action would have been taken against C. gloeosporioides as the species is known to be widespread in California.

California Interceptions:  Colletotrichum boninense has been intercepted at least thrice in shipments of Algaonema sp. from Costa Rica (see ‘Initiating event’).

The risk Colletotrichum boninense 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) – Similar to other species of Colletotrichum, C. boninense requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement may limit the ability of the pathogen to fully establish and spread under dry field conditions in California. Limited regions with conducive climates within California could enable the pathogen to establish.  In particular, C. boninense s. str. can effectively infect and spread to host plants grown under conducive climate conditions in nurseries.

2)  Known Pest Host Range: 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

Risk is High (3) – The host range of Colletotrichum boninense s. str. is very diverse and includes member in the plant families Amaryllidaceae, Bignoniaceae, Podocarpaceae, Proteaceae, Solanaceae, Theaceae, and Araceae.

3)  Pest Dispersal Potential: Evaluate the 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

Risk is High (3) – The pathogen has high reproductive potential and conidia are produced successively.  They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

4)  Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

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 High (3) – Under suitable climates, the pathogen could lower plant growth and value and trigger the loss of markets.

5)  Environmental Impact: Evaluate the environmental impact of the pest on California using these criteria:

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:

– 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 Medium (2) – The pathogen could significantly impact cultural practices, home gardening or ornamental plantings.

Consequences of Introduction to California for Colletotrichum boninense:

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 of Colletotrichum boninense to California = (13).

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 not established.  However, while there is no official record of the establishment of Colletotrichum boninense in California, during the 1980s, CDFA plant pathologists identified C. gloeosporioides in Camelia japonica (Theaceae) and other hosts in the plant family Araceae which are included as host for C. boninense s. str.  These detections were made in northern and southern coastal counties.  At that time specific molecular diagnostic tests were not available to enable the distinction of C. boninense.  It is, therefore, possible that these detections may have included C. boninense s. str.

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:

The possibility that the 2013 detection of C. gloesporoides may have included the now segregate species, C. boninense st. str. and that the latter may already be established in California, can only be ascertained through survey and testing of infected host plants particularly in suspect counties included in early detection reports of C. gloeosporioides .  Subsequent results may alter the herein proposed rating for the pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum boninense s. str. is B.

References:

CABI.  2014.  Colletotrichum boninense datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/

Damm, U., P. F. Cannon, J. H. C. Wouldenberg, P. R. Johnston, B. S. Weir, Y. P. Tan, R. G. Shivas and P. W. Crous.  2012.  The Colletotrichum boninense species complex.  Studies in Mycology 73:1-36; www.studiesinmycology.org

Farr, D. F., & A. Y. Rossman.  Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 7, 2015, from

http://nt.ars-grin.gov/fungaldatabases/

Kitterly, W. R., and A. P. Keinath.  1996.  Fungal disease of aerial parts: Anthracnose. In ‘Compendium of Cucurbit Diseases’.  Edited by T. A. Zitter, D. L. Hopkins, and C. E. Thomas, APS Press The American Phytopathological Society Minnesota, USA, p. 24-25.

Moriwaki, J., T. Sato and T. Tsukiboshi.  2003.  Morphological and molecular characterization of Colletotrichum boninense sp. nov. from Japan.  Mycoscience 44:47-53.

Tarnowski, T. L. B. and R. C. Ploetz.  2010.  First report of Colletotrichum boninense, C. capsici, and a Glomerella sp. as causes of postharvest anthracnose of passion fruit and Florida.  Plant Disease 94:786. http://dx.doi.org/10.1094/PDIS-94-6-0786C .

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.

PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Colletotrichum petchii Damm, P. F. Cannon & Crous, 2012

California Pest Rating for
Colletotrichum petchii Damm, P. F. Cannon & Crous, 2012
Pest Rating: B
PEST RATING PROFILE
Initiating Event:    

In January 2015, the fungal pathogen Colletotrichum petchii, was detected in infected potted Dracaena deremensis (corn plant) in a nursery in Vista, San Diego County, California.  The plants were shipped from a nursery in Keaau, Hawaii. The pathogen was cultured from infected leaves and identified by Suzanne Latham, CDFA plant pathologist.  This detection was considered a new US record and reportable by the USDA. The species identity was confirmed by the USDA PPQ National Mycology Laboratory.  Consequently, the shipment of plants was destroyed.   A permanent rating for Colletotrichum petchii is proposed herein.        

History & Status:

Background:  Colletotrichum petchii was originally discovered in 1925 by Petch and described under a previously existing name, Colletotrichum dracaenae that was detected in dark brown patches on leaves of Dracaena brauni (syn. D. sanderiana) in Sri Lanka.  However, Damm et al., (2012) published the name C. petchii to replace C. dracaenae Petch 1925 which was an illegitimate name according to the International Code of Nomenclature for fungi. [The legitimate name for C. dracaenae is the same name but described by Allescher: C. dracaenae Allesch., 1902.]

The more recent development of species-specific molecular diagnostic tests, particularly since the early 2000s, resulted in changes in taxonomy and nomenclature of fungi within the genus Colletotrichum and eventually led to the recognition of Colletotrichum petchii.  During 2003 to 2012, prior to its being legitimately named, C. petchii was included as a strain of the species C. boninense.  However, researchers indicated that C. boninense actually comprised of a complex of several species.  Then by 2012, through molecular phylogenetic analyses of 86 strains of C. boninense, Damm et al. were able to recognize C. petchii as a separate species. Furthermore, C. boninense was originally described in 2003 as a segregate of the vastly morphological and physiological variable C. gloeosporioides complex (CABI, 2014; Morikwaki et al., 2003).  In the past, isolates of C. boninense were often identified as C. gloeosporioides (Damm et al., 2012).

Hosts: Dracaena spp., Dracaena aletriformis (syn. D. latifolia).D. braunii, D. fragrans (syn. D. deremensis), D. sanderiana,

Symptoms:  Colletotrichum-infected host plants exhibit symptoms of anthracnose which include dark brown leaf, stem and fruit spots and wilting of leaves often resulting in dieback and reduction in plant quality.

Damage Potential:  Anthracnose disease caused by Colletotrichum petchii can result in reduced plant quality and growth.  Estimates of yield/crop loss due to this pathogen have not been reported.  Nursery production of Dracaena as potted plants or in greenhouses are particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  In cultivated fields, disease development may be sporadic as it is affected by levels of pathogen inoculum and environmental conditions.

Disease Cycle:  It is likely that Colletotrichum petchii has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on plant residue in soil, on infected plants, and on seeds.  During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers.   Conidia are transmitted to host plants.  Humid, wet, rainy weather is necessary for infection to occur.  These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem under controlled environments of greenhouses.  Condia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue.

Transmission:  Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution:  Sri Lanka, Italy, China, Netherlands, Germany, and USA.

Official Control:  Colletotrichum petchii is considered a new USA record and reportable to the USDA.

California Distribution: There is no official record of the establishment of Colletotrichum petchii in California, however in 2013 CDFA plant pathologists identified C. gloeosporioides in Dracaena warnickii plants grown in a nursery in San Luis Obispo County, California.  At that time specific molecular diagnostic tests were not available to enable the distinction of C. boninense and C. petchii.  It is, therefore, possible that this detection may have included C. petchii (Suzanne Latham, CDFA, personal communication).  No eliminative action would have been taken against the 2013 nursery detection of C. gloeosporioides which is known to be widespread in California.

California Interceptions:  Colletotrichum petchi has been intercepted once in shipment of potted Dracaena deremensis from Hawaii (see ‘Initiating event’).

The risk Colletotrichum petchii 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) – Similar to other species of Colletotrichum, C. petchii requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement may limit the ability of the pathogen to fully establish and spread under dry field conditions in California. Limited regions with conducive climates within California could enable the pathogen to establish.  In particular, C. petchii can effectively infect and spread to host plants (Dracaena spp.) grown under conducive climate conditions in nurseries.

2)  Known Pest Host Range: 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

Risk is Low (1) – The host range of Colletotrichum petchi is limited to Dracaena spp.

3)  Pest Dispersal Potential: Evaluate the 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

Risk is High (3) – The pathogen has high reproductive potential and conidia are produced successively.  They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

4)  Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

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 High (3) – Under suitable climates, the pathogen could lower plant growth and value and trigger the loss of markets.

5)  Environmental Impact: Evaluate the environmental impact of the pest on California using these criteria:

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:

– 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 Medium (2) – The pathogen could significantly impact cultural practices, home gardening or ornamental plantings.

Consequences of Introduction to California for Colletotrichum petchii:

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 of Colletotrichum petchii to California = (11).

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 not established.  However, while there is no official record of the establishment of Colletotrichum petchii in California, in 2013 CDFA plant pathologists identified C. gloeosporioides in Dracaena warnickii plants grown in a nursery in San Luis Obispo County, California.  At that time specific molecular diagnostic tests were not available to enable the distinction of C. boninense and C. petchii.  It is, therefore, possible that this detection may have included C. petchii (Suzanne Latham, CDFA, personal communication).

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 = 11.

Uncertainty:

The possibility that the 2013 detection of C. gloesporoides may have included the now segregate species, C. petchii and that the latter may already be established in California, can only be ascertained through survey and testing of infected host plants particularly in San Luis Obispo County and neighboring counties.  Subsequent results may alter the herein proposed rating for the pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum petchii is B.

References:

CABI.  2014.  Colletotrichum boninense datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/

Damm, U., P. F. Cannon, J. H. C. Wouldenberg, P. R. Johnston, B. S. Weir, Y. P. Tan, R. G. Shivas and P. W. Crous.  2012.  The Colletotrichum boninense species complex.  Studies in Mycology 73:1-36; www.studiesinmycology.org

Kitterly, W. R., and A. P. Keinath.  1996.  Fungal disease of aerial parts: Anthracnose. In ‘Compendium of Cucurbit Diseases’.  Edited by T. A. Zitter, D. L. Hopkins, and C. E. Thomas, APS Press The American Phytopathological Society Minnesota, USA, p. 24-25.

Moriwaki, J., T. Sato and T. Tsukiboshi.  2003.  Morphological and molecular characterization of Colletotrichum boninense sp. nov. from Japan.  Mycoscience 44:47-53.

Petch, T.  1925.  Additions to Ceylon fungi. III. Annals of the Royal Botanical Gardens. Peradeniya 9:313-328.

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.

PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Phytophthora siskiyouensis Reeser & E. M. Hansen, 2008

California Pest Rating for
Phytophthora siskiyouensis Reeser & E. M. Hansen, 2008
Pest Rating: B
PEST RATING PROFILE
Initiating Event:  

In October 2014, Suzanne Latham, CDFA plant pathologist detected the oomycete, Phytophthora siskiyouensis which was isolated from a diseased alder tree with a bleeding trunk canker in Mill Valley, Marin County, California.  A few months earlier, the pathogen had been detected in some diseased Italian alder trees in Richmond, Contra Costa County, and originally in 2006 from a large planting of Italian alder trees in Foster City, San Mateo County. These detections in California first noted the capability of P. siskiyouensis to cause detrimental disease in alder. Subsequently, there is a need to reevaluate the current status and pest rating of P. siskiyouensis for the proposal of a permanent rating.

History & Status:

Background: Since the discovery of Phytophthora ramorum, causal organism for the Sudden Oak Disease, there has been an increase of surveys throughout the world, for Phytophthora spp. which resulted in the identification of several new species, including P. siskiyouensis.  Phytophthora siskiyouensis was first discovered in 2007 in streams and soils in native forest within sudden oak death epidemic regions of coastal southwest Oregon (Reeser, et al., 2007).  It appears to occur naturally in native forests in south west Oregon and was later found associated with a blighted myrtlewood shoot growing near ground level, and infrequently from tanoak bark cankers.  Furthermore, it was found in Oregon nurseries as a pathogen of alder planting stock but was not observed to cause disease on red alder in natural environments where it was detected in soil and streams (Hansen, et al., 2011; Reeser, et al., 2007).

In California, Phytophthora siskiyouensis was first found associated with bleeding trunk cankers in dying Italian alder trees in Foster City, San Mateo County (Rooney-Latham et al., 2009). In pathogenicity tests, the pathogen was confirmed to be pathogenic on Italian alder trees and potentially pathogenic to red and white alder trees.  Furthermore, it was only detected in tree bark and vascular tissue lesions and not from associated soil and root samples of the diseased trees.  The pathogen was also reported to be associated with dying alder trees in a garden in Melbourne, Australia, but as in California, was not detected in soil around the diseased trees (Smith et al., 2004).  Presently, it is not known if Phytophthora siskiyouensis is endemic to or was introduced to California.

Hosts: Presently, the full range of Phytophthora siskiyouensis is not known.  Reported hosts include, Italian alder (Alnus cordata), European common alder (A. glutinosa), White alder (A. rhombifolia), tanoak (Notholithocarpus densiflorus), California bay laurel/Myrtlewood (Umbellularia californica), and in forest streams or soil (Hansen, et al., 2011; Rooney-Latham et al., 2009; Smith et al., 2004). In pathogenicity tests, Smith et al., (2004) determined that P. siskiyouensis was a potential weak pathogen of Citrus, Acacia, and Eucalyptus seedlings.

Symptoms:  The pathogen causes collar rot in Italian alder trees.  Predominant symptoms produced on alder trees include sparse foliage, dieback in the canopy, and bleeding cankers on the trunks. Canker form primarily at the bases of trunks near the soil line and extend upwards.  Few isolated cankers may form about 2 meters above the soil line.  Trunks may have several small spots or large areas with bleeding lesions which are dark-brown to black on the outer bark.  Below the outer bark, diseased, dark orange-brown tissue is present.  A cinnamon-brown margin is separates cream-colored healthy tissue from diseased tissue which extends through the bark to the vascular cambium and sapwood interface.   Trees with large cankers may show dieback of the canopy however, cankers are not always produced on trees showing dieback (Rooney-Latham, et al., 2009; Sims, 2012). Reeser et al., (2007) noted that in Oregon the pathogen was associated with occasional symptoms on a variety of plants.

Damage Potential: Currently, there are no reports on quantitative economic losses in plant production caused by Phytophthora siskiyouensis. While infected native trees in Oregon occasionally resulted in apparent symptoms on a variety of associated plants, including trunk cankers on tanoaks, the pathogen was found to kill alder trees in California and Australia.  Infestations may result in significant damage and loss in production and stands of host plants by causing collar rot of infected plants. The full host range for this pathogen is yet not known, nevertheless, nursery alders in particular, and plants grown in natural ecosystems are particularly affected.  In general for Phytophthora spp., young seedlings of trees and annual plants may be killed within a few day, weeks or months (Agrios, 2005).

Disease Cycle: Generally, species of Phytophthora that cause root and stem rots survive cold winters or hot and dry summers as thick-walled, resting spores (oospores and chlamydospores) or mycelium in infected roots, stems or soil.  During spring, the oospores and chlamydospores germinate to produce motile spores (zoospores) that swim around in soil water and roots of susceptible hosts. The pathogen infects the host at the soil line causing water soaking and darkening of the trunk bark. This infected area enlarges and may encircle the entire stem of small plants which wilt and eventually die.  On large plants and trees, the infected, necrotic area may be on one side of the stem and become a depressed canker below the level of the healthy bark.  Collar rot canker may spread down the root system. Roots are invaded at the crown area or at ground level.   Mycelium and zoospores grow in abundance in cool, wet weather causing damage where the soil is too wet for normal growth of susceptible plants and low temperatures (15-23°C) prevail (Agrios, 2005).

Transmission:  The pathogen may be spread to non-infected sites through infected plants, nursery and planting stock, seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment and tools.

Worldwide Distribution:  North America: USA; Oceania: Australia.

In the USA, Phytophthora siskiyouensis has been found in California and Oregon (CABI, 2014).

Official Control:  None reported.

California Distribution:  Phytophthora siskiyouensis has been detected on alder in Contra Costa, Marin, and San Mateo Counties (see ‘Initiating Event’).

California Interceptions:  The pathogen has not been intercepted in quarantine shipments of plants.

The risk Phytophthora siskiyouensis 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 High (3) – Phytophthora siskiyouensis has already been detected in few counties.  Within California, it is likely to establish in cool, wet climates in susceptible hosts.  Thus far it has only been detected in alder trees in California.

2)  Known Pest Host Range: 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

Risk is Low (1) – The full host range of Phytophthora siskiyouensis is yet not known.  Reported hosts include, Italian alder, European common alder, white alder, tanoak, and California bay laurel.  It has also been detected in forest streams or soil in Oregon.  Experimentally, it has been shown to be a weak pathogen of Citrus, Acacia and Eucalyptus seedlings.

3)  Pest Dispersal Potential: Evaluate the 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

Risk is High (3) – Phytophthora siskiyouensis is primarily spread artificially via infested soils, plants, nursery and planting stock, seedlings, run-off and splash irrigation water, cultivation equipment and tools that may spread contaminated soil and plant materials to non-infected sites. Thus far, in California, the pathogen has not been isolated from roots and associated soil of infected alder trees.

4)  Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

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 High (3) – Although quantitative economic losses in plant production have not reported, the potential for infected alder  plants to result in collar rot, trunk cankers, and shoot dieback could decrease stands on non-infected plants, increase production costs and cause loss of market of infected  nursery stocks. The potential for the pathogen to survive and spread in infected soils and irrigation water could require changes in normal cultivation practices of host plants.

5)  Environmental Impact: Evaluate the environmental impact of the pest on California using these criteria:

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:

– 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 Medium (2) – Currently, the host range and geographic distribution of P. siskiyouensis are not fully known.  The few known host plants (see ‘Hosts’ above) can be found in natural ecological habitats as well as in nursery environments.  Alder trees are particularly affected by this pathogen.  Subsequently, under favorable climate conditions, natural plant communities and ecosystems, as well as home/urban gardening and ornamentals may be negatively impacted.

Consequences of Introduction to California for Phytophthora siskiyouensis:

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 of Phytophthora siskiyouensis to California = (12).

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 Low (-1). To date, Phytophthora siskiyouensis has been detected in three California coastal counties (Contra Costa, Marin and San Mateo Counties) on alder (Alnus sp.) under similar climate (north coastal environment).

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 = 11.

Uncertainty:

The full host range and in-state distribution of Phytophthora siskiyouensis is not currently known.  To date, in California, the pathogen has only been detected from alder trees in three northern coastal counties.  Continued statewide surveys for Phytophthora spp. occurring in nurseries and natural ecosystems (e.g. restoration sites) will contribute to the present knowledge of this pathogen group as well as that of P. siskiyouensis.  Also, it is not known if P. siskiyouensis is endemic to California or was introduced. Related information gained through further research may affect the current proposed rating of P. siskiyouensis.  

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phytophthora siskiyouensis is B.

References:

Agrios, G. N.  2005.  Plant Pathology fifth edition.  Elsevier Academic Press, Massachussetts, USA.  922 p.

CABI.  2014.  Phytophthora siskiyouensis datasheet (basic) report.  Crop Protection Compendium.  www.cabi.org/cpc/

Farr, D.F., & Rossman, A.Y.  2014.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved November 10, 2014, from http://nt.ars-grin.gov/fungaldatabases/ .

Hansen, E. M., P. Reeser and S. Rooney-Latham.  2011.  Phytophthora siskiyouensis.  Forest Phytophthoras 1(1). doi: 10.5399/osu/fp.1.1.1826

Reeser, P. W., E. M. Hansen and W. Sutton.  2007.  Phytophthora siskiyouensis, a new species from soil, water, myrtlewood (Umbellularia californica) and tanoak (Lithocarpus densiflorus) in southwestern Oregon.  Mycologia 99:639-643.

Reeser, P. W., Sutton, W., and Hansen, E. M. 2008. Phytophthora species causing tanoak stem cankers in southwestern Oregon. Plant Dis. 92:1252.

Rooney-Latham, S., C. L. Blomquist, T. Pastalka and L. R. Costello.  2007.  First report of Phytophthora siskiyouensis causing disease on Italian alder in Foster City, California.  Phytopathology 97:S101.

Rooney-Latham, S., C. L. Blomquist, T. Pastalka and L. Costello.  2009.  Collar rot on Italian alder trees in California caused by Phytophthora siskiyouensis.  Online. Plant Health Progress doi:10.1094/PHP-2009-0413-01-RS. http://www.plantmanagementnetwork.org/pub/php/research/2009/alder/ .

Sims, L.  2012.  Alder (Alnus spp.) – Collar Rot {Phytophthora Canker}.  PNW Plant Disease Management Handbook Printed page URL: pnwhandbooks.org/plantdisease/node/6703 http://pnwhandbooks.org/plantdisease/node/6703/print

Smith, I. A., Cunnington, J., and Pascoe, I. 2004. Another new? species of Phytophthora on alder down under (Australia). P. of the IUFRO Res. Work. Gr. Conf. on Phytophthora Forests and Natural Ecosystems. 11-17 September 2004. Freising, Germany.

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.

PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Colletotrichum orbiculare (Berk. & Mont.) Arx 1957

California Plant Pest Rating for
Colletotrichum orbiculare (Berk. & Mont.) Arx 1957
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

None. A permanent rating for Colletotrichum orbiculare is proposed herein.

History & Status:

Background: Colletotrichum orbiculare is a fungal pathogen causing anthracnose disease of cucurbit plants particularly watermelon, cantaloupe, and cucumber. The species is often known by its synonymized scientific name, Colletotrichum lagenarium and belongs to the taxonomic family Glomerellaceae, within the phylum Ascomycota. C. orbiculare is the asexual (anamorph) stage of the pathogen. The sexual stage (telemorph) with the name Glomerella lagenarium has been reported but is rarely found in nature. Two distinct populations of the pathogen are known: one from watermelon (race 1) and the other from cucumber and melon (race 1 and 3) (Sitterly & Keinath, 1996).

Hosts: The pathogen commonly attacks members of the family Cucurbitaceae, especially melon and watermelon. Hosts include Althaea officinalis (marsh-mallow), Artocarpus heterophyllus (jackfruit), Benincasa hispida (wax gourd), Citrullus lanatus (watermelon), Cucumis melo (melon), Cucumis sativus (cucumber), Cucurbita maxima (giant pumpkin), C. moschata (pumpkin), C. pepo (ornamental gourd), Momordica charantia (bitter gourd) and Trichosanthes cucumerina var. anguinea (snake gourd) (CABI, 2014).

Symptoms: Host plants infected with Colletotrichum orbiculare exhibit symptoms of anthracnose and fruit rot. In California, except for seedless watermelon, anthracnose is unusual on cucurbit crops and can cause leaf, fruit, and/or stem lesions. On cucurbits, leaf spots are usually large (>10 mm diameter) and tan to pale brown with distinct margins. However on watermelon, these foliage lesions are dark brown to black. Brown or black lesions appear on fruit. These lesions grow to 20-30 mm diameter, become sunken, wrinkled and dark, with concentric rings of sub-surface, tiny, black, saucer-shaped asexual structures that containing spores or conidia (acervuli). In wet weather, pink or orange spores ooze from these asexual structures (CABI, 2014; UCIPM, 2008). Fruit is susceptible to infection approximately at the time of ripening and severely infected fruits are often tasteless or bitter and usually invaded by soft rotting bacteria and fungi (Agrios, 2005).

Damage Potential: Anthracnose disease caused by Colletotrichum orbiculare has recently been considered to be particularly important wherever cucurbits are cultivated under highly controlled conditions. High infections may cause formation of numerous leaf lesions and vine defoliation resulting in poor quality fruit and yield loss (Egel, 2014). Watermelon artificially inoculated with C. orbiculare (as C. lagenarium) caused up to 63% losses in yield (CABI, 2014).

Disease Cycle: The species has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on cucurbit plant residue in soil, on infected volunteer plants, and on or in cucurbit seed. During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers. Conidia are transmitted to host plants. Humid, wet, rainy weather is necessary for infection to occur. Condia germinate and grow optimally at 22-27°C and 100% relative humidity for 24 hours. These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem in transplants grown under controlled environments of greenhouses. Condia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue up to 72 hours after deposition. Symptoms are produced about 96 hours after infection. The sexual stage (telemorph) is rarely found in nature (Sitterly & Keinath, 1996).

Transmission: Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution: Colletotrichum orbiculare is widely distributed throughout the world and has been reported from several countries in Asia, Africa, North America, South America, Central America and Caribbean, Europe and Oceania. In the USA it has been found in Alabama, California, Colorado, Connecticut, Florida, Hawaii, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Minnesota, Mississippi, Nebraska, North Carolina, North Dakota, Oklahoma, Pennsylvania, South Carolina and Texas (CABI, 2014; Farr et al., 1989).

Official Control: Currently Israel, Chile and Jordan include Colletotrichum orbiculare on their Harmful Organism List.

California Distribution: in California, Colletotrichum orbiculare has been detected in a greenhouse in Tehama County (Koike et al., 1991).

Historically, it has also been detected in southern coastal region counties which include: San Benito, Monterey, San Luis Obispo, Santa Barbara, Ventura, Los Angeles, Orange and San Diego Counties (K. F. Baker Herbarium, CDFA in The California Plant Disease Host Index by A. M. French, 1989).

Details of the south coastal region detections are not available. Given the absence of reports on the field detection of the pathogen in California, it is likely that the south coastal region detections were mainly limited to greenhouses. On the other hand, those south coastal counties would share a similar climate including higher incidence of rainfall and wind driven rain necessary for infection and establishment of the disease.

California Interceptions: The pathogen has not been intercepted in quarantine shipments of plants.

The risk Colletotrichum orbiculare 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 Low (1) – Colletotrichum orbiculare requires humid, wet, rainy weather for conidia to infect host plants. This is a main reason why the pathogen has not been able to fully establish and spread under dry field conditions in California. It has, however, been detected in controlled greenhouse environments.

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 Moderate (2) – Although the host range for Colletotrichum orbiculare is mainly limited to members of the family Cucurbitaceae, plants, the cultivation of cucurbits, mainly melon and watermelon, is in significant acreage and of major importance in California.

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 High (3) – The pathogen has high reproductive potential and conidia are produced successively. They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

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 High (3) – Under suitable climates, the pathogen could lower crop yield, value and trigger the loss of markets.

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 Medium (2) – The pathogen could significantly impact cultural practices, home gardening or ornamental plantings.

Consequences of Introduction to California for Colletotrichum orbiculare:

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 of Colletotrichum orbiculare to California = (11).

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 (-1). Colletotrichum orbiculare has been reported from counties in the California’s south coastal region however, details of those detections are not available. Given the absence of reports on the field detection of the pathogen in California, it is likely that the south coastal region detections were mainly limited to greenhouses. Nevertheless, those south coastal counties would share a similar climate including higher incidence of rainfall and wind driven rain necessary for infection and establishment of the disease.

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:

As discussed above, there is little to no verifiable evidence of the occurrence of Colletotrichum orbiculare in field environments within California. Such information may strengthen or lower the proposed rating for this pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose of cucurbits pathogen, Colletotrichum orbiculare is B.

References:

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

CABI. 2014. Colletotrichum orbiculare datasheet report. Crop Protection Compendium. www.cabi.org/cpc/

Egel, D. S. 2014. Vegetable diseases: Anthracnose of cucumber, muskmelon, and watermelon. Purdue Extension BP-180-W, Purdue University. https://www.extension.purdue.edu/extmedia/BP/BP-180-W.pdf

Farr, D. F, G. F. Bills, G. P. Chamuris and A. Y. Rossman. 1989. Fungi on Plants and Plant Products in the United States. St. Paul, Minnesota, USA: APS Press, 1252 pp.

Kitterly, W. R., and A. P. Keinath. 1996. Fungal disease of aerial parts: Anthracnose. In ‘Compendium of Cucurbit Diseases’. Edited by T. A. Zitter, D. L. Hopkins, and C. E. Thomas, APS Press The American Phytopathological Society Minnesota, USA, p. 24-25.

Koike S. T., T. E. Tidwell, D. G. Fogle and C. L. Patterson. 1991. Anthracnose of greenhouse-grown watermelon transplants caused by Colletotrichum orbiculare in California. Plant Disease, 75(6):644.

UCIPM. 2008. Cucurbits anthracnose pathogen: Colletotrichum lagenarium. UCIPM Online, Statewide Integrated Pest Management Program, University of California Agriculture & Natural Resources. http://www.ipm.ucdavis.edu/PMG/r116101411.html

Responsible Party:

Dr. 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.

Pest Rating: B

Posted by ls