Category Archives: Plant Pathogens

Plant Pathology (plant diseases)

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

Plant Pathogens, Viruses and viroids

Tomato Yellow Leaf Curl Virus (TYLCV)

California Pest Rating for
Tomato Yellow Leaf Curl Virus (TYLCV)
Pest Rating: B
PEST RATING PROFILE
Initiating Event: 

The risk of infestation of Tomato yellow leaf curl virus (TYLCV) in California is evaluated and a permanent rating is proposed.

History & Status:

Background:    During the early 1960s in Israel, Tomato yellow leaf curl virus was the name first given to diseased tomatoes that in 1959 were found to be infected by an agent identified as a whitefly-transmitted viral agent in the Jordan Valley, Israel.  Since then and in less than 25 years, TYLCV spread worldwide.    TYLCV belongs to the genus Begomovirus in the Family Geminiviridae – which includes whitefly transmitted viruses.  The pathogen is accurately identified by the analysis of DNA sequences. The Israel strain was isolated in 1988 and was the first one to be sequenced in 1991. Sequence comparisons of different geographical isolates revealed that TYLCV is actually a complex of begomovirus species that affect tomato.  Subsequently, begomoviruses affecting tomato were separated into several groups and named accordingly.  Tomato yellow leaf curl virus is the name of the virus isolated in Israel (CABI, 2014; Nakhla & Maxwell, 1998; Fauquet et al., 2000). Seven different species belonging to the Tomato yellow leaf curl virus complex have been identified.

Tomato yellow leaf curl virus was identified in 2007 for the first time from infected tomato plants grown in a greenhouse in Brawley, Imperial County, California (Rojas et al., 2007).  Since then the pathogen has been detected in commercial fields, nurseries and private residences within Imperial and Riverside counties.

Hosts: Solanum lycopersicum (tomato) is the major host.  Other hosts include diagnostic experimental plant species belonging to several families: Datura stramonium, Lycopersicon esculentum, Nicotiana glutinosa, N. benthamiana, Phaseolus vulgaris, Petunia hybrida, and Eustoma grandiflorum (lisianthus).   Other cultivated minor hosts include abelmoschus esculentus (okra), C. annum (bell pepper), C. frutescens (cayenne/chili pepper), Nicotiana tabacum (tobacco), Physalis philadelphica (tomatillo), and Vigna unguiculata (cowpea).  Weeds and other wild hosts include Acalypha australis, Artemisia annua, Ageratum conyzoides (billy goat weed), Convolvulus (morning glory), Chenopodium murale (nettleleaf goosefoot), Cuscuta europaea (European dodder), Datura stramonium (jimsonweed), Malva parviflora (pink cheeseweed), Moringa oleifera (horse-radish tree), Sida acuta (sida), Solanum elaegniflolium (silverleaf nightshade) and S. nigrum (black nightshade) (CABI, 2014; VIDE, 1996; EPPO 2014).

In a survey in Cyprus, Papayiannis et al., (2011) found that 49 plant species were TYLCV hosts belonging to 15 families, namely, Amaranthaceae, Chenopodiaceae, Compositae, Convolvulaceae, Cruciferae, Euphorbiaceae, Geraniaceae, Leguminosae, Malvaceae, Orobanchaceae, Plantaginaceae, Primulaceae, Solanaceae, Umbelliferae and Urticaceae.

Symptoms:  The disease is easily identified when tomato are infected at seedling stage.

Young leaves and shoots are severely stunted resulting in bushy and upright seedling growth.  Leaves exhibit the most diagnostic symptoms of small leaves, upward and inward rolling of the margins, interveinal and marginal yellowing, distinct stunting and often a bushy appearance.  Flowers either do not develop or fall off.  When plants are infected early, they lose vigor and fruit production is reduced or stopped. When infected at a later stage of development, fruit already formed continue to develop more or less normally however, additional fruit are not produced.

Leaf curl symptom is not limited to tomato but also produced in TYLCV-infected varieties of common bean and lisianthus (Eustoma grandiflorum).

Most wild tomato species include members that are either immune or symptomless carriers of the virus. Certain weeds are also asymptomatic (Malva parviflora). It is not known how well whiteflies acquire virus from symptomless hosts (Gilbertson, 2008). Plants used to rear whiteflies are immune to the virus (CABI, 2014).

Damage Potential:  TYLCV is one of the most damaging pathogens of tomato and losses up to 100% in commercial fruit production in fields are not uncommon (UCIPM, 2008).  Yield loss results in fewer numbers of fruit produced.  Fruit present at time of infection remain on the plant but few will set more or less normally.  It has been shown experimentally that the younger the plants are at the time of infection, the more severe is the reduction in fruit yield.  Experimentally, compared to non-inoculated plants, 3-10 week old TYLCV inoculated tomato plants showed 63% reduction in number of fruit, while 15 week old plants did not show significant yield reduction (CABI, 2014).  In the USA, mostly minor losses of less than 10% were noted in 1997-2000 due to aggressive actions taken by tomato growers.

Severe losses in commercial bean production in Israel and southern Spain have been reported (Navot et al., 1992; Navas-Castillo et al., 1999).

Disease Cycle and Transmission: TYLCV is transmitted by the whitefly vector, Bemisia tabaci in a persistent manner.  The vector acquires the virus (acquisition access period) after feeding on an infected plant for 15-30 minutes, then there is a latent period of 18-24 hours within the insect after which the virus can be inoculated into a healthy plant during a feeding period of at least 15 minutes (inoculation access period) by the insect. A single white fly can inoculate more than one plant.  TYLCV is retained within the vector when the latter molts and is detected in every developmental stage of the vector.  It does not multiply within the vector and is not passed on from generation to generation through the eggs of the vector, although research results may be controversial:  Ghanim et al. (1998) detected TYLCV in whitefly eggs that suggested transovarial passage (CABI, 2014; VIDE, 1996).  Whiteflies remain viruliferous for approximately two weeks.  Large populations of B. tabaci moving between crops can cause rapid spread and high levels of disease.

The pathogen is spread over short distance by the white fly vector.  TYLCV is also transmitted by grafting and poorly by mechanical inoculation, but it is not transmitted by contact between plants.  Seed transmission has not been reported.  Over long distances, TYLCV is spread mainly through the movement of infected plants.  As symptoms can take up to 3 weeks to develop, symptomless infected plants can often go unnoticed.  Hitch-hiking, virus-carrying whiteflies can also accompany tomato and other host plants moved over long distances as well as strong winds and storms.

Worldwide Distribution:   TYLCV has been reported from several countries in Asia, Africa, North America (Mexico and USA), Central America and Caribbean, South America (Venezuela only), Europe, and Oceania (CABI, 2014, EPPO, 2014).

In the USA, TYLCV is present in Alabama, Arizona, California, Florida, Georgia, Hawaii, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, and Texas.

Official Control:  TYLCV is included on the Harmful Organism Lists of 49 countries in Asia, Europe, and South America, including Antigua and Barbuda Islands (PCIT, 2014). As a result of the estimated losses caused by TYLCV in 1999-2003, several countries in Australia and The European Union have established strict quarantine measures against the whitefly vector (CABI, 2014).

California Distribution: Imperial and Riverside Counties.

Major tomato-producing regions of California, including the Sacramento and San Joaquin valleys, do not promote the establishment of TYLCV.  According to Gilbertson (2008), the vector is not found in those regions for two main reasons.  First, the vector is intolerant of the region’s cool winter temperatures.  Second, the Central Valley has a natural tomato-free period from late November to early February during which period the amount of virus inoculum is significantly reduced until tomatoes are planted in late winter to early spring.  So, even if TYLCV is able to overwinter during the tomato-free period, it would take a long time for viral inoculum to build up to damaging levels in the field.  The virus is able to infect other host plants however, it builds up quickly on tomato.

There have not been any establishments of any Bemisia tabaci haplotype overwintering populations north of Fresno County due to the cooler winter temperatures and lack of the right amount of degree days for development (personal communication: Dr. Raymond Gill, CDFA Entomologist, 2013).  Nevertheless, it is not unusual for the whitefly vector species to be introduced into and possibly establish within contained controlled environments of nursery greenhouses in northern California regions (CDFA Pest Detection Records and personal communication: Dr. Gillian Watson, CDFA Entomologist).

California Interceptions:  There are no records of TYLCV detected in incoming plant shipments to California.

The risk Tomato yellow leaf curl virus 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) – The establishment of TYLCV within CA is closely related to the establishment of its whitefly vector, Bemisia tabaci. The virus (and the vector) is already established in commercial and urban environments in Imperial and Riverside Counties.  However, the vector is limited to the southern regions of the state as it is intolerant of the cooler winter temperatures present in the main tomato-growing regions in northern California.  Also, the vector is unable to build up to damaging levels because of the tomato-free production period present in the Central Valley.   

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) – While tomato is the main host for TYLCV, minor hosts include moderate numbers of cultivated plants, ornamentals, and weeds belonging to several plant species and families.

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 spread of TYLCV is through artificial means. Short distance spread is mainly through its white fly vector, Bemisia tabaci, whereas long distance spread is mainly through movement of TYLCV-infected plants and strong winds that may move the vector over longer distances than it own capability.

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) – TYLCV is one of the most economically damaging pathogens of tomato.  Incidence and spread of the virus could gravely affect the tomato industry in particular, by lowering crop yield, value, increasing production costs, affecting local and international  markets, negatively change normal cultivation practices to prevent incidence of further occurrence and spread of the virus and its whitefly vector.

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) – Several weeds and wild tomato varieties are considered hosts of TYLCV, however, wild tomato and several weed hosts are asymptomatic and it is not known how well the whitefly vector will acquire the virus from such infected hosts that may comprise natural environments.  The effect on these hosts is not known.  Nevertheless, TYLCV infections may impact home/urban gardening and cultivation of ornamentals.

Consequences of Introduction to California for Tomato yellow leaf curl virus

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 TYLCV 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). 

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:

Up-to-date field data is always needed on the probable establishment and spread of TYLCV beyond the known regions in Imperial and Riverside counties.  Such information would be obtained through periodic surveys of tomato fields.  Also not known is the distribution of the virus in natural environments and the potential that infected natural hosts may play in its possible spread to tomato fields.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Tomato yellow leaf curl virus is B.

References:

CABI   2014.  Tomato yellow leaf curl virus full datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/1695

EPPO, 2014.  Tomato yellow leaf curl virus (TYLCV0).  New PQR database.  Paris, France:  European and Mediterranean Plant Protection Organization.  http://newpqr.eppo.int

Fauquet C. M, D. P.Maxwell, B. Gronenborn, and J. Stanley.  2000.  Revised proposal for naming geminiviruses. Archives of Virology, 145(8):1743-1761; 11 ref.

Ghanim, M., S. Morin, M. Zeidan and H. Czosnek, 1998. Evidence for transovarial transmission of tomato yellow leaf curl virus by its vector, the whitefly Bemisia tabaci. Virology (New York), 240(2):295-303.

Gilbertson, R. L.  2008.  Tomato Yellow Leaf Curl.  UC IPM Pest Management Guidelines: Tomato.  UC ANR Publication 3470.  http://www.ipm.ucdavis.edu/PMG/r783103311.html

Nakhla, M. K and D. P. Maxwell 1998. Epidemiology and management of tomato yellow leaf curl disease. In: Hadidi A, Khetarpal RK, Koganezawa H, eds. Plant Virus Disease Control. St Paul, USA: APS Press, 565-583.

Navas-Castillo, J. S., Sanchez-Campos and J. A. Diaz.  1999. Tomato yellow leaf curl virus causes a novel disease of common bean and severe epidemics in tomato in Spain. Plant Disease, 83:29-32.

Navot, N, M., Zeidan, E. Pichersky, D. Zamir and H. Czosnek.  1992. Use of the polymerase chain reaction to amplify tomato yellow leaf curl virus DNA from infected plants and viruliferous whiteflies. Phytopathology, 82(10):1199-1202.

Papayiannis, L. C., N. I. Katis, A. M. Idris and J. K. Brown.  2011. Identification of weed hosts of Tomato yellow leaf curl virus in Cyprus. Plant Disease, 95(2):120-125. http://apsjournals.apsnet.org/loi/pdis .

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

Rojas, M. R., T. Kon, E. T. Natwick, J. E. Polston, F. Akad, and R. L. Gilbertson.  2007.  First report of Tomato yellow leaf curl virus associated with Tomato Yellow Leaf Curl Disease in California.  Plant Disease, 91:1056.

VIDE.  2014.  Tomato yellow leaf curl bigeminivirus.  Plant Viruses Online: Description and Lists from the VIDE Database.  http://pvo.bio-mirror.cn/descr840.htm

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

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 niederhauserii Abad & J. Abad, 2014

California Pest Rating for
Phytophthora niederhauserii Abad & J. Abad, 2014
Pest Rating: B
PEST RATING PROFILE
Initiating Event:  

None.  A permanent rating for Phytophthora niederhauserii is proposed herein.

History & Status:

Background: In 2003, Abad and Abad reported the discovery of a Phytophthora species associated with necrotic collars, stems and roots of arborvitae (Thuja occidentalis L.) and English ivy (Hedera helix L.) grown in greenhouses in North Carolina.  They named the species, P. niederhauseria and submitted the ITS (Internal transcribed spacer) genetic sequences on GenBank-NCBI before publishing an official description of the species.  Soon other researchers from around the globe found that they were working with the same species based on the similarity of their test ITS sequences with that of P. niederhauseria in GenBank.  The species was discovered in 13 countries and associated with ornamentals, fruit trees and native plants.  However, it was only recently, that an official description of the species was published and the name, P. niederhauserii was validated (Abad et al., 2014).

Hosts: Abad et al., (2014) isolated P. niederhauserii from 33 plant hosts in 25 families from various countries.  A number of shrubs and herbaceous ornamental plants are hosts of the pathogen.  Few agricultural crops are also included.  Thuja occidentals (arborvitae), Hedera helix (English ivy), Abies nordmanniana, Acacia dealbata (Mimosa), Banksia baxteri, Banksia prionotes (acorn banksia), Banksia speciosa, various Begonia hybrids,  Callistemon citrinus, Ceanothus sp., Chamaecyparis lawsoniana, Cistus monspeliensis, C. salviifolius (sageleaf rockrose),  Grevillea olivacea, Heuchera sp. Iris sp. Juniperus sp., Kalanchoe blossfeldiana (kalanchoe), Manihot esculenta, Metrosideros villosa, Peperomia clusiifolia,Pistacia lentiscus, Plumbago sp., Prunus dulcis (almond), Punica granatum, Rhododendron catawbiense (catawba rhododendron), Sinningia speciosa (gloxinia), Spathiphyllum sp., Vitis vinifera (grape), and Xanthorrhoea australis (Farr & Rossman, 2014; Abad et al., 2014).

Symptoms:  Generally, Phytophthora niederhauserii infestations cause symptoms of root and stem collar necrosis resulting in wilting and leaf desiccation or drop in host plants.  In Norway, symptoms of P. niederhauserii infestation on greenhouse-potted begonia, gloxinia and ivy included necrotic roots and stems with necrosis extending to the leaves via the petioles.  Wilting of the entire plant was observed in gloxinia and ivy. In kalanchoe, only root discoloration and stunted plant growth are apparent (Herrero et al., 2008).  In Spain, symptoms on almonds included leaf chlorosis and drop, wilting, cankers and gum exudation.  In spring, symptoms included failure to leaf-out, death of scion and rootstock sprouts (Pérez-Sierra et al., 2010). The pathogen caused collar and root necrosis in boxwood associated with severe wilting and desiccation of foliage (Józsa et al., 2010).

Damage Potential: Quantitative economic losses in plant production due to Phytophthora niederhauserii have not been reported, however, infestations may result in significant damage and loss in production and stands of host plants by causing root and crown/basal stem rots of infected plants. Nursery ornamentals and plants grown in natural ecosystems are particularly affected. Infections may lead to death of the plant.  Generally, annual plants and young seedlings of trees may be killed by the disease within a few days, weeks or months (Agrios, 2005). The pathogen can potentially cause crown rot in grapes – as detected in South Africa and in almonds in Turkey (Abad et al., 2014).       

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:  Infected 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.

Worldwide Distribution:  Widespread.  Thirteen countries, namely, Australia, Hungary, Israel, Italy, Japan, the Netherlands, Norway, South Africa, Spain, Taiwan, Turkey, the United Kingdom and the USA (Abad et al., 2014).

In the USA, Phytophthora niederhauserii has been found in California, North Carolina, South Carolina (Robayo-Camacho et al., 2009; Farr & Rossman, 2014).

Official Control:  None reported.

California Distribution: Phytophthora niederhauserii has been detected in Santa Barbara County and counties within the San Joaquin Valley namely, Kings, Fresno, Kern, Merced, Stanislaus, Madera, San Luis Obispo and Tulare counties (CDFA Plant Pathology Database, 2007; Schmidt et al., 2012).

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

The risk Phytophthora niederhauserii 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 niederhauserii has already been detected in few nurseries in California and has been reported (Schmidt et al., 2012) as an aggressive pathogen of almonds in the San Joaquin Valley of California.  Within California, it is likely to establish in cool, wet climates in susceptible hosts.

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) –Currently at least 33 plant species in 25 families have been reported as hosts of the pathogen.  A number of shrubs and herbaceous ornamental plants are included. Few agricultural crops (almonds and grapes) are also included.  The latter are grown as major crops in 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 (3) – Phytophthora niederhauserii 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.

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 could lower crop yield, increase production costs and cause loss of market of infected nursery stock and agricultural crops. The capability of 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 High (3) – A number of plants in natural ecological habitats are hosts to the pathogen.  Subsequently, natural plant communities, ecosystems, threatened or endangered species as well as home/urban gardening and ornamentals may be negatively impacted.

Consequences of Introduction to California for Phytophthora niederhauserii:

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 niederhauserii to California = (14).

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 High (-3). In California, Phytophthora niederhauserii has been detected in Santa Barbara County and the San Joaquin Valley counties.

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:

Statewide surveys specifically for Phytophthora niederhauserii have not been conducted to include all nursery sites and natural ecosystems (e.g., restoration sites) as well as almond and grapevine cultivation sites.  Subsequent data generated may result in the addition of new host plant species and further distribution of the pathogen within California.  All this may alter the current proposed rating of P. niederhauserii.

Conclusion and Rating Justification:

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

References:

Abad Z. G, and J. A. Abad.  2003.  Advances in the integration of morphological and molecular characterization in the genus Phytophthora: the case of P. niederhauseria sp.nov. Phytopathology 408 93:S1.

Abad, Z. G., J. A. Abad, S. O. Cacciola, A. Pane, R. Faedda, E. Moralejo, A. Pérez-Sierra, P. Abad-Campos, L. A. Alvarez-Bernaola, J. Bakonyi, A. Józsa, M. L. Herrero, T. I. Burgess, J. H. Cunnington, I. A. Smith, Y. Balci, C. Blomquist, B. Henricot, G. Denton, C. Spies, A. Mcleod, L. Belbahri, D. Cooke, K. Kageyama, S. Uematsu, I. Kurbetli and K. Keğirmenci.  2014.  Phytophthora niederhauserii sp. nov., a polyphagous species associated with ornamentals, fruit trees and native plants in 13 countries.  Mycologia, 106 (3): 431-447.

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

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/

Jo´zsa A, J. Bakonyi, L. Belbahri, ZA Nagy, A. Szigethy, G. Boha´r and S.Woodward. 2010. A new species of Phytophthora reported to cause root and collar rot of common boxwood, Nordmann fir and Port Orford cedar in Hungary. Plant Pathology 59:1166–1167.

Pe´rez-Sierra A, A. Leo´n, LA A´ lvarez, S.Alaniz, M. Berbegal, J. Garcı´a- Jime´nez, P. Abad-Campos. 2010. Outbreak of a new Phytophthora sp. associated to severe decline of almond trees in eastern Spain. Plant Disease 94:534–541.

Robayo-Camacho E, Hwang J, Jeffers SN.  2009.  A diversity of species of Phytophthora found on floriculture crops.  Phytopathology 99:S109, doi:10.1094/PHYTO-99-1-0109

Schmidt, L. S., R. G. Bhat, D. A. Kluepfel and G. T. Browne.  2012.  Resistance to Phytophthora in new rootstocks for almond and stone fruits.  Phytopathology, 102:S4.106.

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

Phytophthora hedraiandra de Cock & Man in’t Veld

California Pest Rating for
Phytophthora hedraiandra de Cock & Man in’t Veld
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

Recently, Suzanne Latham, CDFA plant pathologist, detected Phytophthora hedraiaindra in Arctostaphylos pumila samples that were collected from a nursery in Monterey County during an inspection related to an earlier detection of P. tentaculata.   In December 2014, the pathogen had also been detected in Arctostaphylos plants propagated in a nursery in Alameda County.  This nursery had requested the CDFA Plant Pathology Laboratory to test some Arctostaphylos plants for Phytophthora spp. before they were to be released for planting.  The nursery baited the water flow-through the potted plants with Rhododendron and Oregano tissue that were provided by the CDFA Lab and returned the same for analysis.  Suzanne Latham, CDFA plant pathologist, confirmed the detection of Phytophthora hedraiandra in culture from Rhododendron leaf baits.  The collection of official samples and trace forward investigations are currently in process related to this detection.  Phytophthora hedraiandra was initially detected in San Francisco, California 2013 on Arctopstaphylos plants.  Arctopstaphylos native plants extracted from a natural site in San Francisco were propagated at three different nurseries in San Francisco, Berkley, and Santa Cruz.  Similar to the 2014 incident, the water flow-through of potted Arctopstaphylos plants was baited with plant tissue which was then sent to the CDFA Lab for testing.  Cheryl Blomquist, CDFA plant pathologist, identified P. hedraiandra in the samples.  The detection was confirmed by the USDA Lab in Beltsville, Maryland. All potted plants were eventually destroyed.  Phytophthora hedraiandra currently has a Q rating that is herein reassessed 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. hedraiandra.  Phytophthora hedraiandra was first discovered in 2001 on leaf spots of Viburnum sp. in the Netherlands (de Cock & Lévesque, 2004).

Hosts: The full host range of Phytophthora hedraiandra is yet not known.  Presently, only certain species of Rhododendron (azalea) and Viburnum are reported as susceptible hosts (CABI, 2014; EPPO, 2014).  Fagus sylvatica (common beech) is also listed as a host (CABI, 2014; Hejna, et al., 2014).  According to CDFA Plant Pathology Detection Records (2014-2015), Arctostaphylos spp. appears to be a new host for this pathogen.

Symptoms:  Plant symptoms caused by Phytophthora hedraiandra infections may vary with the infected host.  Symptoms in Viburnum include wilting, leaf spots, stem cankers and root and collar rots, while symptoms in Rhododendron include leaf lesions and shoot dieback (Henricot & Waghorn, 2014; Schwingle, et al., 2006, 2007).  Symptoms in Fagus sylvatica include root rot, leaf chlorosis and wilting (Hejna et al., 2014).

Damage Potential: Currently, there are no reports on quantitative economic losses in plant production caused by Phytophthora hedraiandra. However, infestations may result in significant damage and loss in production and stands of host plants by causing root and collar rots of infected plants. Nursery ornamentals 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:  Infected soils, plants, nursery and planting stock, seedlings, run-off and splash irrigation and rain water, cultivation equipment and tools that may spread contaminated soil and plant materials to non-infected sites (Yang et al., 2012).

Worldwide Distribution:  Europe:  Italy, Netherlands, Slovenia, Spain, United Kingdom; North America: USA; Oceania: Australia.

In the USA, Phytophthora hedraiandra has been found in California, Minnesota, and Virginia (CABI, 2014; EPPO, 2014).

Official Control:  None reported.

California Distribution:  Alameda, Monterey and San Francisco Counties (see ‘Initiating Event’).

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

The risk Phytophthora hedraiandra 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 hedraiandra has already been detected in few nurseries in California.  Within California, it is likely to establish in cool, wet climates in susceptible hosts.

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 full host range of Phytophthora hedraiandra is yet not known.  Presently, only certain species of Rhododendron (azalea) and Viburnum, and Fagus sylvatica (common beech) are reported as susceptible hosts.  

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) – Phytophthora hedraiandra 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.

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) – Although quantitative economic losses in plant production have not reported, the potential for infected plants to result in root and collar rot, canker, leaf lesions and shoot dieback could decrease stands on non-infected plants, increase production costs and cause loss of market of infected  nursery stocks. The capability of 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 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) – Currently, the host range and geographic distribution of P. hedraiandra 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.  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 hedraiandra:

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 niederhauserii 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 hedraiandra has been detected in three California coastal counties (Alameda, Monterey and San Francisco Counties) on the same host (Arctostaphylos spp.) under similar climate (coastal nurseries).

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 hedraiandra is not currently known.  To date, in California, the pathogen has only been detected from Arctostaphylos plants propagated in nurseries.  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. hedraiandra.  Consequently, the current proposed rating of P. hedraiandra may be affected.  

Conclusion and Rating Justification:

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

References:

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

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

de Cock A. W. A. M. and C. A. Lévesque. 2004. New species of Pythium and Phytophthora. Studies in Mycology 50: 481-487.

EPPO.  2014.  Phytophthora hedraiandra (PHYTHD).  European and Mediterranean Plant Protection Organization PQR database.  http://www.eppo.int/DATABASES/pqr/pqr.htm.

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/ .

Henricot, B. and I. Waghorn.  2014.  First report of collar and root rot caused by Phytophthora hedraiandra on Viburnum in the UK.  New Disease Reports 29:8. http://dx.doi.org/10.5197/j.2044-0588.2014.029.008.

Hejna M., K. Cerny, L. Havrdova, and M. Mrazkova.  2014.  First report of Phytophthora hedraiandra causing Rhododendron dieback and root rot of Common Beech in the Czech Republic.  Plant Disease 98:1,434.2.  http://dx.doi.org/10.1094/PDIS-04-14-0339-PDN

NAPPO.  2006.  Phytophthora hedraiandra de Cock & Man in’t Veld First detection of Phytophthora hedraiandra in the United States and North America.  North American Plant Protection Organization’s (NAPPO Phytosanitary Alert System): http://www.pestalert.org/viewNewsAlert.cfm?naid=4

Schwingle, B. W., J. A. Smith and R. A. Blanchette, S. Gould, and B. L. Blanchette.  2006.  First report of dieback and leaf lesions on Rhododendrons sp. caused by Phytophthora hedraiandra in the United States.  Plant Disease 90:109. http://dx.doi.org/10.1094/PD-90-0109A.

Schwingle, B. W., J. A. Smith and R. A. Blanchette.  2007.  Phytophthora species associated with diseased woody ornamentals in Minnesota nurseries.  Plant Disease 91:97-102.

Yang, X. P. A. Richardson, S. R. Ghimire, P. Kong, and C. X. Hong.  2012.  Phytophthora hedraiandra detected from irrigation water at a perennial ornamental plant nursery in Virginia.  Plant Disease 96:915.3.  http://dx.doi.org/10.1094/PDIS-07-11-0614-PDN.

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

Bacteria, Plant Pathogens

Rhodococcus fascians

California Pest Rating for
Rhodococcus fascians
 Pest Rating: C 
PEST RATING PROFILE
Initiating Event: 

On April 10, 2014, Dr. Jennifer Randall, Associate Research Professor, New Mexico State University, notified Nick Condos, Director, Plant Health and Pest Prevention Services, California Department of Food and Agriculture (CDFA), of her confirmed identification of the plant pathogen, Rhodococcus fascians associated with abnormal pistachio UCB-1 rootstocks from several orchards in California, as well as from a California nursery in Stanislaus County where the rootstocks had originated. Subsequent communications between CDFA and Craig Kallsen, Citrus and Pistachio Farm Advisor for Kern County, indicated that thousands of pistachio rootstocks obtained from the same nursery and planted in the southern San Joaquin Valley since 2011-2014, were performing poorly and exhibiting similar symptoms to those observed and tested positive for R. fascians by Dr. Randall. The Nursery rootstocks were obtained from the University of California Foundation Plant Services.  Currently, R. fascians is a C rated pathogen by CDFA.  The pest rating for the bacterial pathogen is herein reanalyzed under CDFA’s new pest risk analysis process to reaffirm its permanent rating.

History & Status:

Background: Rhodococcus fascians is a yellow-orange gram positive, aerobic, non-spore forming, non-motile bacteria with cell walls containing mycolic acid.  They may have mycelial growth with fragmentation into rods or coccoid forms. The species was previously known as Corynebacterium fascians, but based on cell wall composition and DNA base composition the species was allocated to the genus Rhodococcus as R. fascians (Goodfellow 1984) in the order Actinomycetales and family Norcardiaceae.

Rhodococcus fascians is a plant pathogen that primarily lives on the exterior surfaces of plants but to a lesser degree, can also be found within plant cells.  However, it is not considered to be systemic in plants.  There are reports of several bacterial isolates identified as R. fascians that were found in various non-plant habitats – including ice and polar seawater, however, none of those isolates have been examined for phytopathogenicity (Putman & Miller, 2007).  To cause plant disease, isolates of R. fascians must contain a plasmid with virulence genes for phytopathogenicity.  Once R. fascians enters a plant, it can produce cytokinin and auxin and alter the normal ratio between the two hormones.  This hormone production can block production of abscisic acid and gibberillic acid in plants.

Hosts: Rhodococcus fascians has a host range that includes 87 genera belonging to 40 plant families (CABI, 2014), however, this is considered a underestimated number.  Putnam and Miller (2007) reported that the number of hosts should be expanded to at least 122 taxa.  They considered several reported hosts as either unconfirmed, without published reports, of uncertain identity, or not naturally infected.  Nevertheless, susceptible hosts include monocots and dicots, woody and herbaceous plants: mostly herbaceous perennial ornamentals, few woody plants, few vegetable crops and strawberry.

In California, detection of Rhodococcus fascians on ornamental plants has been reported (A. M. French: California plant disease host index 2nd edition, updated January 11, 2014). However recently, Stamler et al., (2014) first reported the association of R. fascians on pistachio rootstocks.

Symptoms:  Disease symptoms caused by R. fascians have often been overlooked and attributed to the crown gall bacterium Agrobacterium tumefaciens, viral infection, phytoplasmas, viroids, insect injury, nematodes, genetic causes, chemical substances produced by mixed bacterial populations, hormonal disturbance or crowding of plants in small plants (Putnam & Miller, 2007).

Symptoms caused by R. fascians range from witches’ broom and over-fasciation to leafy gall (Faivre-Amiot, 1967), similar to those caused by growth hormone imbalances.  The level of symptom expression is dependent on the host plant genus, species and cultivar, age of the plant at time of infection (young growing tissue is more sensitive than older maturing tissue), bacterial strain (avirulent or virulent), and on plant growth conditions and the mode of infection. Symptoms in naturally infected plants include, proliferation of buds in leaf axils or at the base of stems; bunches of fleshy thick stems with misshapen and aborted leaves that develop at or below the crown of the host plant; proliferation of partially expanded buds called leafy galls; misshapen thickened leaves or shoots, expanded stems in ribbon-like growth or fasciation (formed when several hypertrophied shoots collapse); adventitious, amorphous growth from veins, petioles, or leaf edges; stunting; abnormal scales on bulbs; infrequent inhibition of root growth (Putnam & Miller, 2007).  Generally, the root system is not affected, although severe infection can result in the main root becoming thickened with the inhibition of secondary roots (CABI, 2014).

In California, pistachio rootstocks associated with R. fascians exhibited symptoms that included shortened internodes, stunted growth, swollen lateral buds, bushy/bunchy growth pattern, twisted roots with virtually no lateral branching, and stem galls (Stamler et al., 2014).

Wounding of a plant host is not necessary for R. fascians infection and the pathogen does not preferentially enter the plant through natural opening.  Symptoms can be produced when the bacteria are on the plant surface (CABI, 2014). However, R. fascians may have a prolonged epiphytic phase prior to symptom expression.   As mentioned earlier, the presence of a plasmid with virulence genes is essential for phytopathogenicity (Putnam & Miller, 2007; Stamler et al., 2014).  Symptoms are more severe and develop more rapidly when wounding occurs.

In nature, plant diseases caused by R. fascians requires moist conditions and moderate temperatures commonly occurring during late fall, mild winters and early spring, and can occur in acidic to slightly alkaline soils (Faivre-Amiot, 1967).

Transmission:  The primary means of introduction of the bacterial pathogen to new, uninfested areas – fields or greenhouses, is most likely through contaminated planting material (Putnam & Miller, 2007; CABI, 2014).  Putnam and Miller (2007) isolated pathogenic R. fascians from symptomatic in vitro plant tissue cultures. The pathogen is also known to be externally seed borne in some hosts including pea, nasturtium, greenhouse geranium, Marguerite daisy and carnation.  Also, the pathogen is spread by irrigation water, water splash or rain and contaminated soil.  The role of insects in natural disease transmission is not known, however under artificial conditions, transmission of R. fascians by aphids (Myzus persicae, M. ascalonicus) leading to disease has been reported (CABI, 2014).

Survival:   It is not known if R. fascians truly resides in soil as do other members of the genus.  However, it has been reported to survive in soils for 3 months or for longer periods of 4-5 years.  Putnam & Miller (2007), hold that R. fascians survives in soil only as long as host tissue remains.  Long term survival in natural environments is due to the ability of the pathogen to tolerate prolonged nutrient starvation. The detection of R. fascians in ice and polar seawater indicates that it can survive for very long periods at low temperatures, which further indicates that periods of chilling temperatures that are often required for certain plants will not kill the pathogen. The pathogen is also able to survive on rotation crops (CABI, 2014).

Worldwide Distribution: Rhodococcus facians is distributed in 22 countries in Europe, Asia (India, Iran, Israel), Africa (Egypt), Guatemala, Canada (British Columbia, Manitoba, Ontario, Saskatchewan), Mexico, Australia (New South Wales), New Zealand, and the USA (19 states, including California).

Official Control: R. fascians is a quarantine pest in Japan, Argentina and Peru (CABI, 2014).

California Distribution: While there has not been a statewide survey for R. fascians, early CDFA detection records of 1950-1983 document the pathogen being widespread in northern and southern, coastal counties, and northern mountain and foothill counties of California.  The 2014 detection of the pathogen on pistachio includes fields and nursery in the Southern San Joaquin Valley (Kern, Tulare and Stanislaus Counties).

California Interceptions:  CDFA records indicate detections of R. fascians in herbaceous ornamental plants grown in nurseries.  It is quite likely that disease symptoms induced by R. fascians were either overlooked or attributed to other pathogens, chemical, hormonal or cultural factors and therefore, never recorded or recorded to a lesser extent than the actual impact caused by the pathogen.

The risk Rhodococcus fascians 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) – Given the already widespread distribution of R. fascians in California.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

Risk is High (3) – R. fascians has a very broad host range of monocots and dicots, woody and herbaceous plants: mostly herbaceous perennial ornamentals, few woody plants, few vegetable crops and strawberry.

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) – As a bacterial pathogen, under optimal growth conditions of high moisture and moderate temperature, R. fascians primarily resides epiphytically on plants, has a high reproduction rate and readily spread through contaminated planting propagative material, seed, soil, and water.

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) – Serious recurring economic losses due to R. fascians can be incurred by the nursery industry. R. fascians infestations could lower crop yield and crop values thereby increasing production costs; infestation of  nursery herbaceous plants and field crops could result in great loss in markets and alter normal cultural practices to insure pathogen-free propagative plant material.

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) – R. fascians may significantly impact ornamental cultivation and home/urban gardening and cultivation practices.

Consequences of Introduction to California for Rhodococcus fascians:

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 R. fascians to California = (14).

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 (-3).  R. fascians is ubiquitous and already established in diverse climate areas throughout 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:

While there currently remains much unknown regarding the biology of R. fascians (Putnam & Miller, 2007), as well its pathogenic relationship with several hosts including pistachio (Stamler et al., 2014), it is not likely that additional information will qualify the pathogen for a higher rating.  Indeed, revelation of further plant hosts, plasmid-borne virulent strains, and detection localities will only strengthen the C-rating of this already widespread pathogen, nevertheless, emphasizing its importance as a bacterial plant pathogen causing serious economic losses to plant production.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Rhodococcus fascians is C.

References:

CABI.  2014.  Rhodococcus fascians datasheet. http://www.cabi.org/cpc/datasheet/15332

Faivre-Amiot A, 1967. Quelques observations sur la presence de Corynebacterium fascians (Tilford) Dowson dans les cultures maraicheres et florales en France. Phytiatrie-Phytopharmacie, 16:165-176.

Goodfellow M, 1992. The family Nocardiaceae. In: Balows A, Trnper HG, Dworkin M, Harder W, Schleifer KH, eds. The Prokaryotes. Berlin, Germany: Springer-Verlag, 1188-1213.

Kallsen, C.  2014.  Rhodococcus fascians associated with some UCB-1 rootstocks.  Kern Pistachio News, University of California Cooperative Extension, April, 2014.

Kallsen, Craig, University of California Cooperative Extension Bakersfield: email to Duane Schnabel, California Department of Food and Agriculture, April 22, 2014.

Randall, Jennifer, New Mexico State University: email to Nick Condos, California Department of Food and Agriculture, April 10, 2014.

Putnam, M.  2014.  Demystifying Rhodococcus fascians.  Digger, February, 2014: 33-37.

Putnam, M. L. and M. L. Miller.  2007.  Rhodococcus fascians in herbaceous perennials.  Plant Disease, 91 (9): 1064-1076.

Stamler, R. A., J. Kilcrease, R. J. Heerama, C. E. Kallsen, and J. J. Randall.  2014.  Rhodococcus sp. associated with Pistachio Bushy Top Syndrome in California and Arizona.  Plant Disease (submitted).

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: C

Posted by ls

Plant Pathogens, Viruses and viroids

Pea Seed-borne Mosaic Virus (PSbMV)

California Pest Rating for
Pea Seed-borne Mosaic Virus (PSbMV)
Pest Rating: B
PEST RATING PROFILE
Initiating Event: 

There is no initiating event.  The risk of infestation of Pea seed-borne mosaic virus in California is evaluated and a permanent rating is proposed.

History & Status:

Background: In 1966 a virus disease of pea was first reported in Europe.  The same virus was also described in Japan as Pea seed-borne mosaic virus. During the early 1980s the virus was also discovered in New Zealand and England and is now known to be widespread throughout the globe due to the movement of infected pea seeds through high international trade.  In California, the pathogen was first discovered in 2004 on pea cultivated in a field in Monterey County.

Pea seed-borne mosaic virus belongs to the genus Potyvirus in the family Potyviridae and RNA viruses group.  The nucleic acid consists of a positive-sense single stranded RNA.  The virus consists of several strains or pathovars that are serologically closely related.  Three strains of PSbMV (P1, P2 and P4) have been identified and the most common strains include P-1 and P-4 from pea and the L-1 from lentil. Usually, differential hosts have been used to identify specific strains (Larsen, 2001).

Hosts: The host range for PSbMV includes at least 47 plant species belonging to 12 families.  However, only three hosts are considered to be economically important, namely, Pisum sativum (pea), Lens culinaris subsp. culinaris (lentil), and Vicia faba (bean).  Chickpea is also a susceptible host however, there is no evidence that it transmitted through contaminated seed.  Other hosts include a wide range of experimental hosts.

Symptoms:  Symptoms on peas are affected by age of plant at the time of infection, temperature, virus strain or pathotype and plant genotype.  Symptoms may develop in as few as 3 days after infection.  Certain pea cultivars never express symptoms (Khetarpal & Maury, 1987). Symptoms may be more severe on plants germinating from infected seed.  Symptoms include general stunting, leaf mild chlorosis, shortening and downward rolling of leaflets, vein clearing and swelling, rosetting (due to reduction of internodal growth), mosaic, distorted flower or seed pods and failure to set pods. However, symptoms disappear soon after infection.  Seed coats of PSbMV-infected seed may become cracked, split or banded and often serve as indicators of possible PSbMV infection although these symptoms may also be caused by physiological or environmental factors.  Contrarily, healthy appearing seeds with normal seed coats may also bear the virus pathogen (CABI, 2014; Larson, 2001).

Damage Potential:  The loss of market due to infected seed is a significant factor in the estimated economic loss caused by the virus.  As much as 36% reduction in pea seed yields are estimated to be due to PSbMV infection (Khetarpal & Maury, 1987).  Seed infections greater than 30% have been reported (CABI, 2014).

Transmission:  The most common means of long-distance transmission of PSbMV is through infected seed.  The virus infects seed internally and all parts of inflorescences from infected plants contain the virus.  Infected seed is an important means of introducing the virus into new, non-infected areas.  Spread from plant to plant is brought about mainly by aphid vectors and mechanical transmission. The virus can be transmitted in a non-persistent manner by 21 aphid species.   The pea aphid (Acyrthosiphon pisum), green peach aphid (Myzus persicae), and cotton aphid (Aphis gossypii) are the most common vectors.  Natural aphid vectors are the pea aphid, cowpea aphid (Aphis craccivora), black bean aphid (Aphis fabae), Dactynotus escalanti, mint aphid (Ovatus crataegarius), and bird cherry-oat aphid (Rhopalosiphum padi). If aphid populations are high and uncontrolled during a growing season, then only a few PSbMV-infected seeds can result in spreading the disease over a large percentage of a field.  Typically, the aphid vector can acquire the virus in 5 min and transmit it after a single probe of one minute or less (Larsen, 2001).  Hampton and Mink (1975) reported that aphids acquire PSbMV and inoculate it in 10-90 sec feeding periods without requiring a latent period.  High aphid populations are favored by cool growing seasons thereby enabling effective spread of PSbMV.

Worldwide Distribution:   PSbMV is distributed worldwide largely due to the distribution of pea germplasm infected with the seed-transmitted virus (Larsen, 2001; Hampton et al., 1993).  It is distributed in Asia: India, Iran, Israel, Japan, Jordan, Lebanon, Nepal, Pakistan, Syria, Taiwan, Turkey, Yemen; Africa: Algeria, Egypt, Ethiopia, Libya, Morocco, South Africa, Sudan, Tanzania, Tunisia, Zambia, Zimbabwe; North America: Canada, USA; South America: Brazil; Europe: Belgium, Bulgaria, Czech Republic, former Czechoslovakia, Denmark, Finland, France, Germany, Netherland, Poland, Romania, Russian Federation, Serbia, Slovakia, Sweden, Switzerland, United Kingdom, Yugoslavia; Oceania: Australia, New Zealand.

In the USA is it has been found in California, Idaho, Maryland, Minnesota, New York, Oregon, Vermont, Washington, and Wisconsin (CABI, 2014; EPPO, 2014).

Official Control:  Since 1995, PSbMV has been listed by Argentina and Brazil as an A1 quarantine pathogen (EPPO, 2014).  The pathogen is on the ‘Harmful Organism List’ for nine countries: Australia, Costa Rica, Georgia, Japan, Nambia, Nauru, South Africa, Taiwan and Uruguay (PCIT, 2014).

California Distribution: Monterey County, California.

California Interceptions:  There are no official records of PSbMV detected in incoming plant shipments to California.

The risk Pea seed-borne mosaic virus 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) – The establishment of PSbMV within CA is closely related to the establishment of its major hosts and associated aphid vector. Cultivation of pea and bean plants requires cool and humid climate – such as is found mainly along the California’s coastal regions.  Already PSbMV is established in Monterey County, California.

2)  Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

Risk is Medium (2) – PSbMV has a moderate host range of 47 plant species belonging to 12 families.  However, the main hosts of economic importance are pea, bean and lentil.  The former two crops are in limited commercial production 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 spread of PSbMV is through infected seed and several (21) Aphid species.  The combination of both agents, plus the high rate of multiplication of the virus within an infected host render the pathogen a high risk potential for spread to non-infected sites.

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) –Incidence and spread of PSbMV could adversely affect pea and bean production in California by lowering crop yield, value, increasing production costs, affecting local and international  markets, negatively change normal cultivation practices to prevent incidence of further occurrence and spread of the virus and its whitefly vector.

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) – Several weeds may be hosts of PSbMV and serve as sources of inoculum acquired by aphids against economically important hosts. However, several weed hosts may be asymptomatic and it is not known how well the whitefly vector will acquire the virus from such infected hosts that may comprise natural environments.  The effect on these hosts in nature is not known.  Nevertheless, PSbMV infections may impact home/urban gardening and cultivation of ornamentals.

Consequences of Introduction to California for Peas seed-borne mosaic virus

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 PSbMV 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 (-1). 

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:

Current field data is always needed on the probable establishment and spread of PSbMV beyond the known infested regions of Monterey County.  Such information would be obtained through periodic surveys.  Also not known is the distribution of the virus in natural environments and the potential that infected natural hosts may play in its possible spread to legume fields.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pea seed-borne mosaic virus is B.

References:

CABI   2014.  Pea seed-borne mosaic virus full datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/1695

EPPO, 2014.  Pea seed-borne mosaic virus (PSBMV0).  New PQR database.  Paris, France:  European and Mediterranean Plant Protection Organization.  http://newpqr.eppo.int

Hampton, R. O and G. I. Mink. 1975. Pea seed-borne mosaic virus. CMI/AAB Descriptions of Plant Viruses. No. 146, 4pp. Wellesbourne, UK: Association of Applied Biologists. http://www.dpvweb.net/dpv/showdpv.php?dpvno=146.

Hampton, R. O, J. M. Kraft, F. J. Muehlbauer. 1993. Minimizing the threat of seedborne pathogens in crop germ plasm: elimination of pea seedborne mosaic virus from the USDA-ARS germ plasm collection of Pisum sativum. Plant Disease, 77(3):220-224

Khetarpal R. K. and Y. Maury. 1987. Pea seed-borne mosaic virus: a review. Agronomie, 7(4):215-224

Larsen, R. C.  2001.  Pea Seedborne mosaic virus.  In: Compendium of Pea Diseases and Pests Second Edition.  St.Paul, USA: APS Press, 37-38.

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

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

Fungi, Plant Pathogens

Kweilingia divina (Syd.) Buriticá 1998

California Pest Rating for
Kweilingia divina (Syd.) Buriticá 1998
Pest Rating: A
PEST RATING PROFILE
Initiating Event: 

In December 2014, Kweilingia divina was detected in a quarantine interception of bamboo leaves showing symptoms of rust, imported from Florida to California.  The detection was made by Contra Costa Agricultural Commissioner’s office inspector and the associated pathogen was identified by Suzanne Latham, CDFA plant pathologist. This rust fungus had also been intercepted in 2006 by Los Angeles County in a similar shipment of bamboo from Hawaii.  All infected plants were destroyed.  The risk of introduction and establishment of Kweilingia divina in California is evaluated here and a permanent rating is proposed.

History & Status:

Background:  The bamboo rust fungal pathogen, Kweilingia divina was originally ascribed as the type species of the genus Dasturella (D. divina) which was detected in infected bamboo leaves (Bambusa sp.) in 1943 (Mundkur & Kheswalla, 1943).  However, in 1998, Dasterulla divina was renamed Kweilingia divina.

Kweilingia divina requires two different kinds of hosts to complete its life cycle (heteroecious), producing two types of specialized spores on each host, namely urediniospores and teliospores on bamboo and spermatia (pycniospores) and aeciospores on its alternate host, Catunaregam spinosa (mountain pomegranata). The pycnial and aecial state are not known in the New World (Farr & Rossman, 2015).

Hosts: Several species of bamboo including, Bambusa balcooa, B. bambos, B. domestica, B. multiplex, B. mutabilis, B. oldhami, B. polymorpha, B. tulda, B. shimadai, B. tuldoides, B. vulgaris, Dendrocalamus brandisii, D. hamiltonii, D. latiflorus, D. longispathus, D. strictus, Ischurochloa stenostachya, Ochlandra scriptoria, O. travancorica, Oxtenanthera sp.,O. abyssinica, O. nigrociliata, Phyllostachys bambusoides,Pleioblastus sp., Pseudoxytenanthera ritcheyi, Pseudosasa japonica var. usawai, P. usawai, Shibataea kumasaca,  Thyrsostachys oliveri, T. sianensis, and the alternate, non-bamboo host Catunaregam spinosa (Blomquist et al., 2009; Cummins, 1971; Nelson & Goo, 2011; Farr & Rossman, 2015).

Symptoms: On bamboo, initial symptoms of infection are the presence of water-soaked, pinhead-sized flecks on the lower surface of leaves.  Soon yellowish-orange to brown, elongate, interveinal, linearly aligned fruiting structures (uredinia) develop and produce urediniospores.  On the corresponding side of the upper leaf surface, grayish-brown to dark brown lesions with yellowish halos for along the parallel veins.  Numerous lesions may develop on a leaf surface or coalesce to form larger areas of tan-colored necrotic blight. Over time, brownish black linear structures (telia) develop within the lesions on the lower leaf, either inside old, degenerating uredinia or separately.  Severely infected leaves defoliate prematurely (Nelson & Goo, 2011).  The alternate host, Catunaregam spinosa is not present in California but is native to tropical Southeast Asia and tropical Africa.

Damage Potential:  Bamboo is not a main cultivated crop in California.  However, bamboo plants are grown and sold mainly as nursery ornamentals and commercial plantings in private residences, public parks, amusement parks, and other environments.  The bamboo rust disease is a threat to these limited yet economically important regions where bamboo is grown in California.  Rusted bamboo leaves are not only aesthetically unsightly but also negatively impact plant growth.  Severe infestations of bamboo rust can result in defoliation and reduction in plant growth, vigor and stand.  Once established in California, containment and management of the rust pathogen will 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: Asia: India, China, Hong Kong, Japan, Pakistan, Taiwan, Malaysia; Africa: Cote d’Ivoire, Ghana, Nigeria,    North America: Mexico, USA; Oceania: Australia, New Calendonia, Samoa; Caribbean Islands: Cuba, Dominican Republic, Jamaica, Puerto Rico, Trinidad and Tobago, West Indies, Virgin Islands; Central America: Costa Rica; South America: Brazil, Guyana, Colombia, French Guiana (Farr & Rossman, 2015).

In the USA it has been reported from the Hawaiian Islands (Oahu, Hawaii, Kauai, and Maui).  The detections in California resulted in the eradication of the disease (Blomquist et al., 2009; Nelson & Goo, 2011).

Official Control: None reported.

California Distribution:  Bamboo rust pathogen, Kweilingia divina, is not established in California.  All 2006 and 2014 intercepted shipments of infected bamboo plants were destroyed (see ‘Initiating Event’).

California Interceptions:  Kweilingia divina was intercepted in Los Angeles in 2006 and in Contra Costa County in 2014.

The risk Kweilingia divina 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) – Kweilingia divina is able to establish a widespread distribution in California wherever bamboo is grown.

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 Kweilingia divina is mainly limited to several species of bamboo. The alternate host does not exist 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 infective spores of Kweilingia divina 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 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) – Severe infestations of the bamboo 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 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 the criteria below.

A.  The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B.  The pest could directly affect threatened or endangered species.
C.  The pest could impact threatened or endangered species by disrupting critical habitats.
D.  The pest could trigger additional official or private treatment programs.
E.  The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.

Risk is High (3) – Outbreaks of the disease could have significant impact on established bamboo ecosystems. Commercial bamboo plantings in public parks, resorts and plantings in private residences may be impacted by the bamboo rust pathogen subsequently triggering additional treatment programs.

Consequences of Introduction to California for Kweilingia divina

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 Kweilingia divina 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: Kweilingia divina is not established in California (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 = 13

Uncertainty:

Future detection surveys for Kweilingia divina in nurseries and established bamboo groves 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 Kweilingia divina is A.

References:

Blomquist, C. L., J. M. McKemy, M. C. Aime, R. W. Orsburn and S. A. Kinnee.  2009.  First report of bamboo rust caused by Kweilingia divina on Bambusa domestica in Los Angeles County, California.  Plant Disease 93: 201. http://dx.doi.org/10.1094/PDIS-93-2-0201A

Cummins, G. B. 1971.  The rust fungi of cereals, grasses and bamboos.  Springer-Verlag New York Inc.  570 p.

Farr, D. R., and A. Y. Rossman.  2015.  Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved March 18, 2015, from http://nt.ars-grin.gov/fungaldatabases/

Johnson, G. I.  1985.  Rust (Dasturella divina) of Bambusa spp. in Australia.  Australasian Plant Pathology 14:54-55.

Mundkur, B.B., and K. F. Kheswalla. 1943. Dasturella: A New Genus of Uredinales. Mycologia 35:201–206.

Nelson, S., and M. Goo.  2011.  Kweilingia rust of bamboo in Hawaii.  College of Tropical Agriculture and Human Resources, University of Hawaii at Mānoa. Plant Disease PD-74.

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: A

Posted by ls