It's Time

Doing Something Different with Bacterial Ring Rot

Published in the May 2013 Issue Published online: May 29, 2013 Neil C. Gudmestad, University Distinguished Profes
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Albert Einstein is credited with saying, "Insanity is doing the same thing over and over again and expecting different results." Some question whether he actually said that, but I believe this statement is very appropriate when considering the recurring epidemics of bacterial ring rot suffered by the U.S. potato industry.

During my 36 years in the potato industry I have been involved with no fewer than four major epidemics of BRR, with smaller localized outbreaks here and there. These epidemics tend to occur on an eight- to 12-year cycle. Most epidemics take three to four years to run their course, after which the industry enjoys a four- to eight-year hiatus from the disease.

The last major BRR epidemic began in Western North America about 2003, spreading eastward until finally ending in the Midwest in 2006-2007. A BRR outbreak in the Western U.S. was quite severe in 2012. Whether or not this outbreak will expand into a pandemic (widespread epidemic) has yet to be determined. There are extraordinary measures being taken by the entire industry to assure a pandemic does not occur, but only time will tell us whether these measures are successful. The sad reality is that BRR outbreaks do not need to happen. We have the knowledge and technology to more effectively manage this very manageable potato disease.


Basic Principles

Plant disease management strategies fall under a few basic principles: exclusion, eradication (sanitation), protection and resistance. BRR management strategies fall under only two principles. Ring rot bacteria can be excluded from a farm. An effective method of exclusion is to use certified seed that has been post-harvest tested, providing assurance that it is BRR-free. BRR can be effectively eradicated by using pathogen-tested, tissue culture-derived, limited-generation seed stocks. We can also use sanitizing agents to effectively eliminate or eradicate the pathogen from a farm. An important concept to remember is all certified seed lots begin their lives ring rot-free but become contaminated due to poor sanitation.

While as we can protect plants from blights by using fungicides, we cannot protect potato plants from becoming infected with BRR. And while genetic resistance is effective for managing most potato diseases, resistance to BRR only creates symptomless carriers-"Typhoid Marys"-that can harbor the bacterium and act as sources of inoculum for other susceptible varieties. Varietal resistance to BRR is the bane of the potato industry. Thus, as an industry, we are left with excluding the disease and using sanitation to effectively manage it.


Poor Sanitation

It is my assertion that BRR is a disease of poor sanitation. Although I have no direct evidence of this, the cyclic nature of BRR in the U.S. certainly suggests this to be true. Consider what I stated earlier. BRR occurs in eight- to 12-year cycles, each cycle lasting three to four years. During a BRR pandemic, I believe the potato industry enters into a period of heightened awareness where sanitation-the washing and sanitizing of all potato equipment and storages-occurs with increased fervor. These activities effectively control the disease until it becomes "invisible."

This increased attention to sanitation continues for a time after the pandemic has waned, but eventually the invisibility of the disease creates a false sense of security and the industry returns to a reduced level of sanitation. Corners are cut, and there is an inadvertent intermingling of potato production equipment and vehicles used in the growing and transport of commercial potatoes and seed potatoes. Over time, the pathogen builds up and a BRR outbreak is initiated, starting the cycle all over again. As an industry we need to break this cycle.

Because of the reoccurrence of BRR epidemics I have joined into a collaborative research and outreach effort with two colleagues, Dr. Phil Nolte, University of Idaho and Dr. Jonathan Whitworth, USDA-ARS. Together we propose to perform studies that will potentially improve BRR management.

Many in the industry are already aware that I am a proponent of post-harvest testing of seed potatoes to provide additional assurance that the seed used by the industry is not infected with BRR. However, while we have the technology to effectively do this, the infrastructure to test all seed lots in the U.S. is currently lacking. The logistical constraints in testing tubers that are costly to ship and bulky to store are horrendous and an impediment to implementation. We propose to develop methods that can be used during the growing season to detect the bacterium. This will substantially alleviate the logistical problems associated with the current post-harvest testing while also providing more timely information for the industry.

We also propose to improve the testing of varieties for susceptibility to BRR. Varieties that become infected with ring rot but fail to show symptoms can act as reservoirs of infection for other varieties. In the mid-1980s when I chaired a "National Task Force for the Eradication of BRR," this was of such concern that the task force recommended the industry "characterize the reaction of potential new potato varieties to BRR," which most public breeding programs now do. However, a recent trend in the industry has been the use of varieties developed elsewhere in the world. None of these varieties have ever been tested for their reaction to BRR. We could have dozens of "Typhoid Marys" in the industry and not even know it. This needs to be resolved.

It should be obvious that I firmly believe that BRR is a problem of the entire industry, not just the seed sector. As such, we must work together to solve the problem. As an industry, we can ill afford to continue to operate as we have been and expect a different result. To continue to do so would be, quite frankly, insane. If you agree, my colleagues and I ask for your support of our research and outreach initiatives we believe will have a significant impact on effective management of BRR in the future. PG