Seed industry representatives are urging California growers to get their cucurbits seed certified as free of the Cucumber Green Mottle Mosaic Virus (CGMMV) before planting because of several outbreaks that have occurred over the past two seasons.
Ric Dunkle, senior director of seed health and trade for the American Seed Trade Association (ASTA), told WG&S this is a serious concern, and if the virus is found in a field, the crop has to be destroyed. He said it is incumbent upon growers to have their seed tested before planting to prevent the spread of this virus.
The ASTA executive said the current issue surfaced in California in the summer of 2013. “It was initially detected in July of 2013 in several fields of cucumbers and melons that were being grown for seed production in the Central Valley,” he said.
Those fields were destroyed and barred from growing cucurbit seed for the following two years. “We thought it had been discovered and eradicated before it spread,” said Dunkle.
However, a year later, in July 2014, the virus was again found in several fields of seedless watermelon in the San Joaquin Valley, most notably in Kern County. Dunkle said those fields were transplants that came from a nursery. In the seedless watermelon, the virus took the shape of destroying the watermelon from the inside out. “When you cut open the watermelon, it was rotten inside,” said Dunkle.
Again fields had to be destroyed.
Dunkle said the seed industry and nursery industry have been alerted to the problem and seed is being tested and certified as virus free before it is sold and grown. But he said growers also need to be vigilant as seed sometimes comes from alternate sources and is not certified.
Betsy Peterson, associate director of technical services and programs for the California Seed Association, Sacramento, CA, said the statewide group is helping to eradicate the virus by reaching out to growers and publicizing the issue. A brochure developed by ASTA is available on the California Seed Association's website (calseed.org) that explains the issue and informs growers as to what they should do. She urged growers to download the nine-page pamphlet, which has step-by-step advice as to testing seed, recognizing infected fields and eradicating the virus.
The brochure states that the virus itself was first described in 1935. It has long caused problems in Europe, Asia, the Middle East and more recently in Canada. The 2013 discovery in the San Joaquin Valley was its first noted presence in the United States.
The brochure describes the disease in the following manner: “Cucumber green mottle mosaic is caused by the cucumber green mottle mosaic virus (CGMMV), which is a rod-shaped, microscopic (300 nm long x 18 nm wide) particle. The virus is easily sap and seed transmissible, and it survives for long periods in infected crop debris. Transmission in seed has been most frequently reported in cucumber but it can occur in other species as well. The virus can be introduced into a crop production in many ways, but contaminated seed and soil are among the most common.”
While CGMMV is a cousin of the far-reaching Tobacco Mosaic Virus (TMV), which has many host plants, CGMMV has a narrow host range limited primarily to cucurbit species, including watermelon, melon, cucumber, pumpkin, squash and gourds, according to the ASTA brochure.
The biggest concern is that the disease is easily transferred. “In some environments and production cultures, CGMMV can be especially problematic due to the ease with which it is transmitted and its stability and long viability in plant debris, in soil or on greenhouse or equipment surfaces,” reads the literature about the virus. “The damage it causes to the host plant and fruit can be extensive, resulting in substantial yield losses.”
The virus does present itself in leaf disfiguration and there are field tests that can detect it, but the seed association executives say the best way to combat it, is to use seed free of the problem. All sources of seed, according to the brochure, should be tested and certified with a “negative” or “no evidence” of CGMMV.
Unfortunately that step does not end the grower’s due diligence. Though it is a great first step and a negative test offers assurance that the virus does not exist in that seed, it is not a guarantee that the entire seed lot is free from the virus. “Regularly inspect seedlings, beginning at about the two true leaf stage of growth,” cautions the brochure. “Note that symptoms of CGMMV most likely will be subtle and difficult to recognize when plants are small.”
If the virus is detected, the impacted area needs to be destroyed. In addition, the virus can be spread from workers’ clothes and tools, plant trays and any mechanical equipment that was used with the infected plant. Anything that came in contact with the virus should be destroyed or sterilized.
The brochure notes that while there is only limited information on cultivars that are resistant to the virus, there is a seed treatment available for seed found to be infected.
Both the American Seed Trade Association and the California Seed Association are conducting seminars and other outreach programs to spread the word and educate the seed industry, nurseries and growers as to the problem, its causes and solutions. ASTA is holding an accredited workshop in Florida in late January, in association with an industry conference, and is urging people to attend to help spread the word. Information about this program is available on the ASTA website (amseed.org).
Closer to home, the 2015 National Watermelon Association Convention will be held in La Quinta, CA, in February and will have some type of session devoted to the problem (nationalwatermelonassociation.com).