News on the Grow
Ralstonia Outbreak
Several U.S.growers can now add a new disease to their repertoire: Ralstonia solanacearum biovar3 race 2. One of the vascular, bacterial agents that causes southern bacterialwilt, R. solanacearum biovar 3 race 2 was recently discovered in a limitednumber of geranium cuttings that were produced offshore, shipped to U.S.rooting stations and eventually rerouted throughout the Eastern, Southern andMidwestern United States.
Because of its inclusion in the U.S. AgriculturalBioterrorism Protection Act of 2002 as “potentially posing a severe threatto plant health or plant products,” this most recent disease importationcaused a reaction from Animal and Plant Health Inspection Service (APHIS) andUnited States Department of Agriculture (USDA) and a temporary quarantine ofhundreds of greenhouses.
How it Happened
The disease originated from a minor infestation of sevenconfirmed ‘Americana Dark Red’ geranium stock plants in Goldsmith Plants’Kenyan facility. According to Goldsmith’s Don Snow, less than 100 cuttings weretaken from the contaminated stock plants and unintentionally introduced into theUnited States in a routine shipment during weeks 44-46 (October 27-November 16)to two U.S. greenhouses, Glass Corner Greenhouse in Michigan and Pleasant ViewGardens in New Hampshire. Plants were rooted for five weeks and subsequentlyshipped to customers during weeks 49-51 (December 1-December 21).
On February 10, the USDA Plant Protection and Quarantine(PPQ) Center officially confirmed the presence of R. solanacearum biovar 3 race2 in samples collected from greenhouses in Wisconsin, Indiana and Illinois.After the February 13 destruction of approximately 50,000 cuttings (total) atGlass Corner and Pleasant View, both operations resumed shipping cuttings thathad not originated in Kenya.
On February 14, the USDA stopped all geranium shipments fromKenya to the United States until further notice. This has impacted Goldsmith,Fischer and Oglevee, which each have stock facilities in Kenya. As of presstime, there have been no reported outbreaks at any of the other breeders, andthis quarantine is not expected to dramatically impact the 2003 seasons.
The last date of importance is the February 27 release ofthe USDA/APHIS action plan. At approximately 35 pages long, the action plangives a detailed account of how to respond to symptoms. As much of thisinformation is of importance only to those greenhouses on the quarantine list,we will not go into the details of the Plan in this article. Those interestedcan find the Action Plan at any of the Web sites listed at the end of thisarticle. You can also find a 12-page summary of the Plan at the Society ofAmerican Florists’ (SAF) Web site.
Because of commingling, and possible cross contamination,during rooting and shipping to and from Glass Corner and Pleasant View, thenumber of greenhouses receiving suspect plants is expected to numberapproximately 150 but could be as many as 800. While these greenhouses arecurrently under quarantine, time and testing have revealed relatively few confirmedcases of R. solanacearum biovar 3 race 2.
It is important to remember that the only greenhouses thatshould be placed under quarantine are those that received geranium cuttingsfrom Glass Corner between November 4, 2002 and January 24, 2003 (weeks 45-4) orfrom Pleasant View between November 4, 2002 and February 14, 2003 (weeks 45-7).
What Happens Next?
The nearly two-week delay between the first notice of thedisease and the follow-up is due to the complexity of the situation and theagricultural security concerns. Ralstonia solanacearum biovar 3 race 2 wasplaced on the bioterrorism list because it is devastating to importantagriculture crops such as potatoes, tomatoes, beans and tobacco, and as such,USDA/APHIS needed to take extra precaution to ensure the protection of thesecrops.
APHIS has worked with states and scientific authorities andgotten information from the industry (most notably Goldsmith, SAF and the twoeffected rooting stations) to develop a plan that will be as workable forgrowers as possible, yet ensure disease eradication. In the interim, the delayhas led to uncertainty for both state regulators and the geranium industry.
Fearing that any introduction of Ralstonia on geraniumcuttings could damage the U.S. potato industry, some have urged that allimported cuttings be banned — a move that was introduced last year and onethat would cause substantial disruption of the nearly $300 million U.S.geranium industry.
“Long term,” explained SAF Senior Director ofGovernment Relations, Lin Schmale, “we are working to get USDA to provideofficial recognition to the Geranium Bacterial Disease Initiative. Currently,the major breeding companies have voluntarily formed a committee for theself-regulation of clean stock facilities and virus indexing to prevent theimportation of diseases such as Xanthamonos and Ralstonia.”
“In the future,” continued Schmale, “we thinkofficial recognition is necessary for the continued importation of cuttings tosustain the geranium market, 50 percent of which originates offshore. APHISrecognizes that the geranium industry is important so they are going to workwith us to solve the problem we have right now, and they are going to continueto work with us to set up a system whereby we can ensure that geranium cuttingswill continue to come into the United States.”
What to Do
Though it is expected that the current outbreak will becontained by publication, growers still need to watch their crops for anygeranium or nicotiana plants that show signs of disease under the warmtemperatures necessary to finish a good geranium crop.
Symptoms of Ralstonia solanacearum biovar 3 race 2 arereportedly similar to those of Xanthamonas, another strain of southernbacterial wilt, and include wilting plants and abnormal yellowing of leaves.This strain of Ralstonia doesn’t spread easily from plant to plant, exceptthrough recirculated irrigation water or stem-to-stem transmission via cuttingknives or manual cleaning and pinching when the laborer has not sanitizedbetween plants. R. solanacearum biovar 3 race 2 can tolerate much coolertemperatures than other strains, though it remains dormant in the cold. It canalso lay dormant in soil and water indefinitely. Growers can easily avoidspreading the disease by simply removing and isolating wilted plants andavoiding subirrigation of geranium and nicotiana plants.
If you suspect you might have R. solanacearum biovar 3 race2, contact Goldsmith Plants at (800) 549-0158, your local university extensionagent or APHIS at (301) 734-3266. Other good sources of information include :APHIS headquarters, www.aphis.usda.gov/ppq; the National Plant Protection Organization’sPhytosan-itary Alert Web site, www.pestalert.org; the Society of American Florists, www.safnow.org;American Nursery and Landscape Association, www.anla.org; OFA, www.ofa.org; andPurdue University, www.ppdl.purdue.edu/ppdl/hor03/02-24.html.
–Bridget White
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