Cucurbit Yellow Stunting Disorder Virus (CYSDV)

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:

– 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) – 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:

– 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 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:

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) – 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.

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) – 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).

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). 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 .

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.