Cucumber Green Mottle Mosaic Virus (CGMMV) in California Seedless Watermelon Fields

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November 17, 2014


Subject:  Cucumber Green Mottle Mosaic Virus (CGMMV) in California Seedless Watermelon Fields


To:  State and Territory Agricultural Regulatory Officials


In July 2014, a grower in San Joaquin County, California, noticed deterioration in seedless watermelon fruit quality in one of his fields. Initial samples were sent to the University of California at Davis for identification; CGMMV was diagnosed from the submission. The California Department of Food and Agriculture (CDFA), in conjunction with the local County Agricultural Commissioner, subsequently sampled the field. CDFA’s Plant Pest Diagnostics Center detected CGMMV, which was then confirmed by the United States Department of Agriculture (USDA) Beltsville laboratory. This virus, which occurs in certain areas of Europe and Asia, is a tobamovirus that affects cucumber and different types of melons. This is a seed-borne virus that spreads in the field in irrigation water or by contact with equipment, people, and animals.


Delimitation surveys were conducted in the area of the positive field and other fields farmed by the grower; four additional fields were found infested in San Joaquin County. Upon confirmation of the virus, CDFA and the Animal and Plant Health Inspection Service (APHIS) immediately initiated trace-back and trace-forward activities. To date, plants from seven different seed lots have been found positive in the field. The seed lots have been tested by CDFA or third party labs, all with negative results. Seed from the seven different seed lots were grown by two separate transplant nurseries and delivered to the growers as seedlings. Transplants were not tested prior to delivery to growers.


Trace-back activities on positive seed lots from San Joaquin County led to the detection of a positive watermelon field in Fresno County and one positive watermelon field in Kern County. Local county agricultural commissioners have implemented containment, eradication, and other abatement measures on all positive fields. As part of these measures, the three growers with positive fields have implemented sanitation procedures for field equipment and are planning to rotate crops to non-hosts for a two-year period. An APHIS working group has been formed and will review options for addressing the virus incident in California. The detections are considered to be transient and under official control.


APHIS confirmed the first U.S. detection of CGMMV in July 2013 in a melon seed field in Yolo County, California. The North American Plant Protection Organization posted an alert on December 6, 2013. The plants were destroyed, and the grower replanted with a non-host crop. The acreage continues to be monitored and volunteer plants tested and destroyed. All volunteer plants that were sampled after harvesting the non-host crop were negative for CGMMV in 2014.


For more information about CGMMV, you may call National Policy Manager Deborah McPartlan at 301-851-2191 or National Operations Manager Robert Bailey at 970-494-7569.




Osama A. El-Lissy

Deputy Administrator

Plant Protection and Quarantine