Category Archives: Viruses and viroids

Tomato Yellow Leaf Curl Virus (TYLCV)

June 1, 2015 Admin

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

Plant Pathogens, Viruses and viroids

Pea Seed-borne Mosaic Virus (PSbMV)

April 9, 2015 Admin

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.

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).

-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:

Pest Rating: B

Posted by ls

Plant Pathogens, Viruses and viroids

Pepino Mosaic Virus (PepMV)

April 7, 2015 Admin

California Pest Rating for

Pepino Mosaic Virus (PepMV)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

In January 2015, Tongyan Tian, CDFA Plant Pathologist, detected Pepino mosaic virus(PepMV) in two official tomato samples collected from plants grown in a greenhouse in San Diego County. The virus has been previously reported by researchers who collected non-official samples also from greenhouse tomatoes in Camarillo, Ventura County, California (Ling et al., 2008). The current regulatory status of PepMV and its potential risk of infestation in California are reassessed here for the proposal of a permanent rating.

History & Status:

Background: Pepino mosaic virus was first described in 1980 when it was isolated from pepino (Solanum muricatum) plants that were collected in 1974 from the coastal region of Peru (Jones et al., 1980). Following its original detection, it was not until 1999 that this pathogen was discovered infecting tomato plants grown in many greenhouses in the Netherlands, and later in the early 2000 in the UK, France and Germany. Since then, it initially spread to several countries in Europe but was subsequently eradicated from Croatia, Czech Republic, Norway, and Slovakia (EPPO, 2014a). Soon it was reported worldwide as a significant disease of greenhouse tomatoes in North America, South America, Asia and Africa. In North America, PepMV was first reported in 2001 (French et al., 2001). In their study of a US isolate of PepMV, Maroon-Lango and other scientists first reported the detection of the virus in tomato samples obtained from California (Maroon-Lango et al., 2003).

Pepino mosaic virus belongs to the genus Potexvirus in the family Alphaflexiviridae and RNA viruses group. Two strains of the virus are currently recognized: the pepino strain and the tomato strain (CABI, 2014). Ling (2007) reported that almost all North America PepMV isolates belonged to the European tomato strain. This was confirmed by Ling et al. (2008) in their study of genetic diversity and distribution of PepMV genotypes in North America. These scientists found four major genotypes of PepMV in the North America and only the European (EU) genotype in California.

Hosts: Pepino mosaic virus was originally described on pepino (Solanum muricatum). The natural and experimental host range is limited primarily to Solanceous plants. In addition to pepino, major and main hosts of PepMV are Solanum lycopersicum (tomato), S. melongena (eggplant) and S. tuberosum (potato). Natural infections have not been observed in potato and eggplant crops (EPPO, 2014b). During surveys in Peru the pathogen was found to be naturally present in several wild Lycopersicum species (L. chilense, L. chmielewskii, L. parviflorum, L. peruvianum) (EPPO, 2014b). Ocimum basilicum (basil) is a minor host. A number of wild and weed plants are hosts including, Amaranthus graecizans (tumbleweed/pigweed), A. retroflexus (red-root amaranth), A. viridis (green amaranth), Calendula arvensis, Chenopodium murale, Chrysanthemum segetum, Convolvulus arvensis, C. humilis, Datura stramonium (jimsonweed), Lycopersicon pimpinellifolium (currant tomato), Malva neglecta, M. nicaeensis, M. parviflora, M. sylvestris, Nicotiana glauca (tree tobacco), N. rustica (wild tobacco), Plantago lagopus, P. major, Solanum nigrum (black nightshade), Sonchus asper, S. oleraceus (common sowthistle) and S. tenerrimus (CABI, 2014; EPPO, 2014a, 2014b).

Symptoms: Symptoms may depend on climate conditions and become more distinct under low light conditions. Because of the variable influence of climate, leaf symptoms may be weak and difficult to observe thereby enabling PepMV-infected plants to escape unnoticed. Initial symptoms on tomato plants include small yellow leaf spots. However later, older, mature leaves may exhibit mottling, while top leaves may show slight curling. Fruit may show orange mottling which may differ between trusses (cluster of small stems bearing flowers and fruit) in a single plant. In Peru, young leaves of infected pepino exhibited yellow mosaic, while in the Netherlands affected tomato plants showed yellow spots, mild interveinal chlorosis and sometimes minor malformation (enation) of leaves. In UK, affected plants showed leaf distortion, chlorosis and bubbling of leaf surfaces, stunted and distorted plants (EPPO, 2014b; Mumford & Jones, 2005).

Damage Potential: Tomato plants infected with PepMV do not always result in significant economic damage since fruit symptoms may be absent. On the other hand, fruit setting may be delayed and yield affected. The virus can cause significant crop losses if early infections are not eliminated (EPPO, 2014b). Greenhouse-grown plants are particularly affected by the virus.

Transmission: Pepino mosaic virus is a very contagious pathogen that is transmitted mainly through mechanical means including contaminated tools, hands, clothing, direct plant to plant contact, grafting, cuttings, and seeds. High concentrations of the virus can be present in plant materials, leaves, fruits and roots of infected plants. The virus can be present in the seed coat of immature and mature tomato seeds, but not within the seed (embryo) (Ling, 2008). Damage or death of roots may release the virus in soil and drainage/irrigation water. Experimentally the virus has been shown to be spread by contact with bumble bees (Bombus terrestris, Bombus spp.) used as pollinators of tomato plants (EPPO, 2014b; CABI, 2014).

Worldwide Distribution: Asia: Syria, Turkey; Africa: South Africa; Europe: Austria, Belgium, Bulgaria, Cyprus, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, Netherlands, Poland, Spain, Switzerland, United Kingdom; North America: Canada, Mexico, USA; South America: Chile, Ecuador, Peru (EPPO, 2014a, CABI, 2014).

The recorded absence of Pepino mosaic virus from China, Taiwan, Madagascar, Morocco and Guatemala is considered unreliable (EPPO, 2014a; CABI, 2014).

In the USA it is present in Alabama, Arizona, California, Colorado, Florida, Maryland, Minnesota, Oklahoma, and Texas.

Official Control: Currently, Pepino mosaic virus is on the ‘Harmful Organism List’ for 45 countries: Albania, Austria, Belgium, Brazil, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Guatemala, Holy See (Vatican City State), Honduras, Hungary, India, Ireland, Italy, Japan, Republic of Korea, Latvia, Lithuania, Luxembourg, Malta, Monaco, Montenegro, Netherlands, New Zealand, Poland, Portugal, Romania, San Marino, Serbia, Slovakia, Slovenia, SPaid, Sweden, Switzerland, Taiwan, Turkey and United Kingdom (PCIT, 2014).

In California, PepMV is currently a Q-rated, quarantine pathogen.

California Distribution: Greenhouse environments within San Diego and Ventura Counties.

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

The risk Pepino 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 High (3) – PepMV is likely to establish wherever its hosts are cultivated or grow naturally in California. Tomato, the primary host, is a major crop that is widely cultivated in the State.

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

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

Risk is Low (1) – The host range is limited primarily to Solanaceous plants of which tomato is the primary host that is cultivated over significant acreage throughout California. Eggplant and potato are also affected, although natural infection of both crops has not been reported.

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) – Pepino mosaic virus is a very contagious pathogen that is artificially spread mainly through mechanical means including contaminated tools, hands, clothing, direct plant to plant contact, grafting, cuttings, and seeds. It is externally seed-borne, and is also spread through infected planting materials. Experimentally, it has been transmitted by contact with bumble bees. Since symptoms are not always readily recognized, there is the potential for this virus to spread rapidly and unnoticed within nursery greenhouse environments as well as to outdoor field environments.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

– 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) – PepMV could lower tomato yield, value and marketability particularly when infected fruit are symptomatic. Due to its contagious nature soil and irrigation water may become contaminated when infected roots and plant residue in soil are damaged or break down, thereby causing changes in normal cultivation practices.

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

Score the pest for Environmental Impact. Score:

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

Risk is Low (1) – Several Solanaceous weeds have been experimentally shown to be hosts of PepMV. Natural infestations of such hosts could serve as reservoirs for the pathogen – although this would need to be confirmed through further research. The virus could negatively affect home/urban gardening and cultivation of tomato and eggplant in particular.

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 PepMV to California = (11).

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 = 10

Uncertainty:

The presence and distribution of PepMV in California agricultural field production and environmental sites is not known. Such information would be obtained through periodic surveys and may affect the current proposed rating. Due to the nature of its transmission, it is possible for the virus to escape detection and spread to non-infected sites.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pepino mosaic virus is B.

References:

CABI 2014. Pepino mosaic virus full datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/1695

EPPO, 2014a. Pepino mosaic virus (PEPMV0). New PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://newpqr.eppo.int

EPPO. 2014b. Pepino mosaic virus. European and Mediterranean Plant Protection Organization. http://www.eppo.int/QUARANTINE/Alert_List/viruses/PEPMV0.htm (Panel review date 2014-03).

Ferguson, G. 2001. Management of Pepino mosaic virus in greenhouse tomatoes – factsheet. Modified November 13, 2013. Ontario Ministry of Agriculture, Food and Rural Affairs. http://www.omafra.gov.on.ca/english/crops/facts/01-017.htm .

French, C. J., M. Bouthillier, M. Bernardy, G. Fergusen, M. Sabourin, R. C. Johnson, C. Masters, S. Godkins and R. Mumford. 2001. First report of Pepino mosaic virus in Canada and the United States. Plant Disease 85:1121.

Jones, R. A. C., R. Koenig, D. E. Lesemann. 1980. Pepino mosaic virus, a new potexvirus from pepino (Solanum muricatum). Annals of Applied Biology, 94(1):61-68

Mumford, R. A., and R. A. C. Jones. 2005. Description of Plant Viruses: Pepino mosaic virus. Association of Applied Biologists 411 (DPV 350 revised version). http://www.dpvweb.net/dpv/showdpv.php?dpvno=411 .

Ling, K. S., 2007. The population genetics of Pepino mosaic virus in North America greenhouse tomatoes. Phytopathology 97:S65.

Ling, K. S., 2008. Pepino mosaic virus on tomato seed: virus location and mechanical transmission. Plant Disease, 92:1701-1705.

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

Responsible Party:

Pest Rating: B

Posted by ls

Plant Pathogens, Viruses and viroids

Potato Spindle Tuber Viroid

March 16, 2015 Admin

California Plant Pest Rating for

Potato Spindle Tuber Viroid

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

On December 16, 2013, CDFA was notified by USDA APHIS of the detection of potato spindle tuber viroid (PSTVd) in three Cestrum samples that were shipped under federal permit from California to Illinois. The detection was made by Ball Horticultural Company Plant Pathologist, and communicated to USDA APHIS as per federal permit requirement that APHIS is notified within 10 days on receipt of permitted materials if the permitee detects a pathogen that is not widely prevalent in the State from which the infected material was obtained.” The Cestrum plant samples came from plants raised in a Nursery greenhouse in San Diego County, CA. Subsequently, there is a need to reevaluate the current status and pest rating of PSTVd as a necessary step toward dealing with the current and future detections of this pathogen in California.

History & Status:

Background: Potato spindle tuber viroid is the first recognized viroid that was discovered in 1971 as the causal agent of the potato spindle tuber disease. The disease itself was first discovered in potato fields in New Jersey, USA (Martin, 1922). The 1971 study led to discovery of viroids which are small naked single-stranded, covalently closed, circular molecule of infectious RNAs that multiply autonomously in plant cells and lack a coat protein as they are too small to coat for a single protein. They infect plant cells and are replicated within the plant nucleus. PSTVd consists of 359 nucleotides and is the type species of the genus Pospiviroid.

Hosts: Potato is considered the main host of PSTVd large due to the presence of serious symptoms and large scale outbreaks. Other symptomatic hosts include tomato and pepper. Symptomless infections have been reported on Persea americana (avocado) and mainly solanaceous ornamentals: Brugmansia spp., Chrysanthemum sp., Calibrachoa sp., Cestrum spp., Dahlia sp., Datura sp., Lycianthes rantonnei, Petunia sp., Physalis peruviana, Solanum pserdocapsicum, Streptosolen jamesonii, Solanum jasminoides, Solanum muricatum, Ipomoea batatas (sweet potato) and wild Solanum spp.

Symptoms: In potato, symptom expression is influenced by potato cultivar, viroid strain, environmental conditions and method of inoculation (Pfannenstiel and Slack, 1980; Diener, 1987; Owens and Verhoeven, 2009). Symptoms include severe or barely distinct growth reduction, smaller vines, plants appear more erect and with smaller leaves than healthy, non-infected ones. Also, leaflets are darker green, sometimes with rolling and twisting. Tubers may be small, elongated (spindle-shaped), misshapen and cracked. Tuber eyes are pronounced and sometime borne on knob-like protuberances.
Infected tomatoes show growth reduction which may develop into permanent stunting with occasional death or recovery. Top grow is chlorotic sometimes turning to reddening and/or purpling causing leaves to become brittle. Flowers and fruit fail to develop as stunting begins. Very mild symptoms are produced on infected peppers in the form of slight distortion or ‘waviness’ of the leaf margins near the top of infected plants (Lebas et al., 2005). Infected solanaceous ornamentals do not exhibit any symptoms.

Damage Potential: PSTVd attacks all potato varieties causing severe losses. Up to 24% reduction in tuber yields are reported with mild strains of PSTVd and 64% with a severe strain (Singh et al., 1971). According to Pfannenstiel and Slack (1980) reduction of tuber weight depended on the potato cultivar and length of time they were infected with PSTVd. Plant age at the time of infection and the number of infected plants are factors that determine the amount of yield loss in tomatoes, reportedly from a few to 10% of plants (CABI International, 2013).

Transmission: PSTVd can infect all or most parts of susceptible plants. The viroid is mechanically transmitted and spread mainly through knives used for cutting infected and healthy tubers. Other means by which infected sap of diseased plants is transmitted to healthy plants include normal cultivation equipment and practices. Also, it is readily transmitted by infected plant material, namely cuttings, tubers, and micro-plants. Symptomless ornamental plants may serve as a source of inoculum. It is also transmitted by pollen, seed – especially for crops propagated by botanical seed, and by contaminated mouth parts of several insect vectors including aphids (Agrios, 2005, CABI International, 2013).

Worldwide Distribution: PSTVd is present in several countries in Europe, although in few occurrences for certain countries. Erratic outbreaks have been reported in tomato and substantial infections of ornamental plants have been reported. Effective measures have reduced the incidence of PSTVd in those crops but it has not been eradicated. However, the viroid was eradicated from Finland and France (CABI International, 2013). It has also been reported in Asia: China, Turkey, India, Iran, Israel, Japan, Afghanistan, Azerbaijan, Bangladesh, and the Republic of Georgia; Africa: Egypt, Nigeria, (absent from Kenya & South Africa – unreliable record according to CABI International 2013); Costa Rica; South America: Peru, Venezuela, Brazil, and Uruguay (it was eradicated from Argentina); Oceania: New Zealand, (it was eradicated from Australia); North America: Mexico, USA. It was successfully eradicated in seed potato production in the USA and Canada.

Official Control: Countries that require phytosanitary certification of PSTVd-free plant commodities imported from the USA include: Israel (tomato and petunia seeds), Austria (solanaceous seeds), Bosnia and Herzegovina (potato tubers), Chile (sweet potato and potato seeds and in vitro plantlets), Columbia (potato plantlets and seeds), India (tomato seeds), Macedonia (potato tubers), Mexico (tomato seedlings and potato in vitro plantlets), Morocco (potato tubers for propagation and consumption), New Caledonia (potato tubers for propagation) and Yemen (pepper and tomato seeds). At least 78 countries worldwide consider PSTVd an actionable pathogen but do not require phytosanitary certification. It is quite probable that these countries may require official certification in the event that PSTVd becomes further established within the USA.

California Distribution: There are no reports of PSTVd being established in field or natural environments within California – that would indicate an established distribution. However, PSTVd was reported for the first time in 2010 in tomatoes grown in commercial greenhouses in Ventura County (Ling, et al., 2010). The 2013 detection of PSTVd was made from infected Cestrum spp. nursery stock (C. fasciculatum Newellii, C. elegans Smithii, and C. elegans) also grown in greenhouses. It is likely that the 2010 PSTVd infected plants were destroyed and appropriate sanitary measures led to the eradication of the pathogen in the affected greenhouses. Similar eradicative measures will most likely be taken against the recent 2013 detection.

California Interceptions: There are no state reports of PSTVd detections in plant materials intercepted within or at points of entry in California.

The risk Potato spindle tuber viroid 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) as shown by the 2010 and 2013 detections of PSTVd in California greenhouses. Suitable climates for potato, tomato and other host plants would also favor the establishment of PSTVd.

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). Potato and tomato are grown in significant acreages throughout the State. Ornamental plants appreciably increase the host range of this pathogen.

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): PSTVd multiply autonomously in infected plant material and are easily transmitted through various means.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

– 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): PSTVd infected potato tubers could lower crop yield, crop value, trigger loss of market through the imposition of quarantine regulations by other countries and states, can influence normal cultural practices and is vectored by insects.

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

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): Incidence of PSTVd could require additional official and private treatments, impact cultural and horticultural practices, at the very least.

Consequences of Introduction to California for potato spindle tuber viroid:

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 = 14 (High).

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: PSTVd is not established in California (0). PSTVd has only been detected in nursery plants contained in greenhouses. Those detection would have led to eradicative and greenhouse sanitary measures. They do not indicate the establishment of the pathogen in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 14 (High).

Uncertainty:

Information of the source of the pathogen is not known. The pathogen has not been reported from environments outside greenhouses.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Potato spindle tuber viroid is A.

References:

Agrios, G. N. 2005. Plant Pathology. Fifth edition. Elsevier Academic Press. 922 p.
CABI International. 2013. http://www.cabi.org/cpc/?compid=1&dsid=43659&loadmodule=datasheet&page=868&site=161

Diener TO, ed., 1987. The Viroids. New York, USA: Plenum Press.

Martin WH, 1922. “Spindle tuber”, a new potato trouble. Hints to Potato Growers, New Jersey State Potato Association, 3:8.

Lebas BSM, Clover GRG, Ochoa-Corona FM, Elliott DR, Tang Z, Alexander BJR, 2005. Distribution of potato spindle tuber viroid in New Zealand glasshouse crops of Capsicum and tomato. Australasian Plant Pathology, 34(2):129-133.

Ling, K. S. and D. Sfetcu. 2010. First report of natural infection of greenhouse tomatoes by Potato spindle tuber viroid in the United States. Plant Disease, 94:1376.

Owens RA, Cress DE, 1980. Molecular cloning and characterization of potato spindle tuber viroid cDNA sequences. Proceedings of the National Academy of Sciences USA, 77:5302-5306.

Owens RA, Verhoeven JTJ, 2009. Potato spindle tuber. External factsheets. Minnesota, USA: APSnet, unpaginated. http://dx.doi.org/10.1094/PHI-I-2009-0804-01.

Pfannenstiel MA, Slack SA, 1980. Response of potato cultivars to infection by the potato spindle tuber viroid. Phytopathology, 70(9):922-926.

Singh RP, Finnie RE, Bagnall RH, 1971. Losses due to the potato spindle tuber virus. American Potato Journal, 48:262-267.

Responsible Party:

Pest Rating: A

Posted by ls

Plant Pathogens, Viruses and viroids

Cucurbit Yellow Stunting Disorder Virus (CYSDV)

March 16, 2015 Admin

California Plant Pest Rating for

Cucurbit Yellow Stunting Disorder Virus (CYSDV)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

The risk of infestation of Cucurbit yellow stunting disorder virus in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background: Cucurbit yellow stunting disorder virus CYSDV belongs to the genus Crinivirus in the family Closteroviridae. As indicated by its name, the pathogen causes cucurbit yellow stunting disorder which is primarily a disease of cucurbits such as, watermelon, melon and squash. CYSDV isolates have been reported from different countries and can be divided into two distinct groups. One group contains isolates from Spain, Lebanon, Jordan, Turkey and North America while the other group contains isolates from Saudi Arabia (EPPO, 2014; CABI, 2014).

Cucurbit yellow stunting disorder virus was originally discovered in the Middle East. In North America, the disease was first discovered in 2006 in southern California’s Imperial Valley, near Yuma, Arizona, and Sonora, Mexico infecting various types of squash including cantaloupe, honeydew, melon and watermelon. In 2007, the virus was also discovered in Florida – although it is not clear how the virus spread to California and Florida. Isolates of CYSDV from Florida and California are genetically identical (Durham, 2011).

The life cycle of the virus is dependent on its whitefly vector, Bemisia tabaci. In tests using melon plants, the vector required 18h or more to acquire the virus during feeding on CYSDV-infected plants and inoculations periods of 24 hours or more to achieve transmission rates of over 80% (CABI 2014).

Hosts: The natural hosts are restricted to Cucurbitaceae: watermelon, melon, cucumber, and ornamental gourd (Cucurbita pepo). Incidental host plants include Cucurbita maxima, Lactuca sativa and Medicago sativa. Cucurbit maxima and Lactuca sativa are also experimental hosts. Other hosts include weeds belonging to Amaranthaceae, Chenopodiaceae, Malvaceae, Solanaceae, Brassicaceae and Asteraceae. The virus is capable of infecting plants in seven plant families besides Cucurbitaceae (Durham, 2011).

Symptoms: Symptoms can take 3 to 4 weeks to develop following infection. Symptoms in CYSDV-infected cucumber and melons initiate as an inter-veinal mottle on older leaves and intensify as leaves age (Abou-Jawdeh, 2000). Infected cucumber plants show chlorotic mottling, yellowing and stunting while yellowing and severe stunting is exhibited on infected melon plants. Symptoms on Cucurbit pepo have not been reported. Several CYSDV-infected weeds and alternate plants such as alfalfa and lettuce can be symptomless.

Damage Potential: The virus can cause serious damage to cucurbit production resulting in complete loss in fruit yield and quality and plant death, especially in regions where the whitefly vector is well established during the growing season Durham (2011). Serious economic problems occur in countries that have Mediterranean climates. Melons produced from CYSDV infected plants have reduced sugar levels, even though they may appear healthy.

Transmission: CYSDV is spread by the whitefly, Bemisia tabaci as it feeds and carries the virus from plant to plant. All biotypes of B. tabaci known to exist in North America can transmit the virus, including biotypes A, B and Q. The virus is transmitted over long distances through the movement of infected plants (particularly cucurbit plants). As symptoms develop in 3 to 4 weeks following infection, it is possible for the virus to be transported in symptomless plants. Also, it is possible to spread CYSDV over long distances through virus-carrying whiteflies that may accompany transported plant materials. All stages of the whitefly vector can be carried on plants for planting. Also, virus-carrying whiteflies can move long distances with high winds. The virus is infectious within whiteflies for up to 9 days. CYSDV is not transmitted mechanically and is not seed-borne (Davis et al., 2012).

Survival: Even with a relatively narrow host range, CYSDV was able to overwinter in California and Arizona in 2006-07. While the incidence of the virus was low in spring planted melons in 2007 it was high in fall-planted melons in the Imperial and Yuma Valleys in both years (Davis et al., 2008).

Worldwide Distribution: Asia: China, Iran, Israel, Jordan, Lebanon, Saudi Arabia, Syria, Turkey, United Arab Emirates; Africa: Egypt, Morocco, Tunisia; Europe: Cyprus, Greece, Portugal, Spain; North America: Mexico, USA (Arizona, California, Florida, Texas) (CABI, 2014; EPPO, 2014).

Official Control: Presently, Georgia, Honduras, Japan and the Republic of Korea list CYSDV have included CYSDV on their ‘Harmful Organism lists’ (USDA PCIT, 2014). In 2004, CYSDV was added to the A2 action list by the European and Mediterranean Plant Protection Organization (EPPO) and member countries are encouraged to regulate it as a quarantine pest, however, there are no specific measures against the pathogen in Europe (EPPO, 2005, 2014).

California Distribution: Imperial Valley, Imperial County.

California Interceptions: There are no official records of CYSDV intercepted in incoming plant material shipments to California.

The risk Cucumber yellow stunting disorder 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:

Risk is Medium (2) – CYSDV is established in the Imperial Valley, southern California. Its further spread to non-infected sites is limited by the distribution of its vector, Bemisia tabaci which to date, has not been found in natural cooler climates of northern California counties.

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) – The natural host range is restricted to Cucurbits in the family Cucurbitaceae (which are grown extensively in the lower Sacramento Valley and in limited production in San Joaquin and Imperial Valleys). Additional hosts include plants in seven families other than Cucurbitaceae that can serve as source plants for the whitefly vector which then can carry the virus back to cucurbits.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

Risk is High (3) – The virus is able to thrive in climates that are favorable for its vector. Its potential for spread is always artificial being completely dependent on the distribution of its vector and infected plant materials. Therefore, factors that increase movement and activity of the vector and infected plants will also influence that of the virus.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

– 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) – CYSDV infections could lower crop yield and value, increase production costs, trigger loss of market, and the virus is vectored by the whitefly, Bemisia tabaci which would require implementation of management strategies to minimize the risk of the introduction and establishment of the virus in non-infected regions within California.

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

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) – Infestations of CYSDV could significantly impact home/urban gardening of cucurbits and non-cucurbit host plants resulting in the imposition of additional official or private treatment programs in order to prevent spread of the virus and virus-carrying whitefly vector.

Consequences of Introduction to California for Cucurbit yellow stunting disorder 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 CYSDV to California = (12).

Evaluation is Low (-1). CYSDV is established in one suitable climate/host region (Imperial Valley) in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11

Uncertainty:

While CYSDV is established in the Imperial Valley and there have been no further reports of its spread to other intrastate regions, targeted surveys for the pathogen have not been conducted in other cucurbit production sites. The distribution and establishment of the virus is largely dependent on the distribution and established infestations of virus-carrying Bemisia tabaci. Subsequently, detections outside the Imperial Valley may alter the proposed rating for this virus pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Cucurbit yellow stunting disorder virus is B.

References:

CABI. 2014. Cucurbit yellow stunting disorder virus datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/17070 .

Davis, R. M., T. A. Turini, B. J. Aegerter and J. J. Stapleton. 2008. Cucurbit yellow stunting disorder. University of California Agriculture & Natural Resources, UCIPM Online, Statewide Integrated Pest Management Program.
http://www.ipm.ucdavis.edu/PMG/r116100211.html .

Durham, S. 2011. Combating Cucurbit yellow stunting disorder virus. http://www.ars.usda.gov/is/pr/2011/110309.htm .

EPPO. 2005. Cucurbit yellow stunting disorder crinivirus – European and Mediterranean Plant Protection Organization data sheet on quarantine pests. OEPP/EPPO bulletin 35:442-444.

EPPO. 2014. Cucurbit yellow stunting disorder virus (CYSDV0). European and Mediterranean Plant Protection Organization PQR database. http://www.eppo.int/DATABASES/pqr/pqr.htm .

USDA PCIT. 2014. United States Department of Agriculture, Phytosanitary Certificate Issuance & Tracking System (PCIT). https://pcit.aphis.usda.gov/PExD/faces/ViewPExD.jsp .