Zero Tolerance Policy
Bacterial ring rot (BRR) is a “zero tolerance” disease, which means that if a single positive plant is found in a field the entire seed lot can be rejected. Due to recent changes in Idaho, all seed lots are now lab tested for BRR. It’s the first state to take such drastic measures, but experts say the move is necessary.
“The change that Idaho’s made is a very big step in the right direction,” said Phil Nolte, University of Idaho Extension seed specialist. “Idaho’s move to begin testing is kind of leapfrogging ahead of the other seed programs in the U.S. This rather dramatic gesture that they’ve just made in instituting a testing program for bacterial ring rot is a very big step and we think it will go a long way toward making sure that we don’t have a repeat anytime in the near future.”
“The bacterium is very easily spread during seed cutting and handling processes,” said Neil Gudmestad, potato pathologist at North Dakota State University. “If a tuber goes through a mechanical cutter and it has ring rot it can spread to literally hundreds of other seed pieces. You can go from having a very small incidence of the disease to a catastrophic epidemic in a specific field in a very short period of time.”
BRR is further exacerbated by the fact that the disease can remain in a latent or symptomless state for two to three years, depending on the cultivar, Gudmestad said.
“The fact that this pathogen can remain symptomless for a long period of time makes it very difficult to manage in a seed field,” he said.
Making the issue further complicated is the fact that the bacterium infects the potato’s vascular tissue, specifically the xylem, which is responsible for moving water and nutrients from the soil up the roots to the leaves. Because it affects the xylem the primary symptom it produces is wilt.
“There are lots of different things that cause wilt,” Gudmestad said. “So when it does manifest itself, it’s not necessarily distinguishable from a lot of other diseases. They decided to make this zero tolerance because a lot of these types of factors.”
Alan Westra, Idaho Crop Improvement Association’s southeast area manager, manages the largest seed potato program in the United States. He said the zero tolerance policy is particularly timely, since Idaho is currently experiencing a flare-up of the disease.
“The disease flares up every decade or so – it’s always around, but we get these flare-ups – and everyone gets concerned because the disease can cause pretty severe economic losses,” Westra said.
“In the case where you have a disease that is seedborne, and it’s not spread by insects or by the wind or rain or anything else, and it doesn’t survive in the soil, a very effective way of controlling it is to put zero tolerance on the presence of the disease in seed potatoes,” he said.
The traditional approach to managing BRR is through field inspections. Inspectors walk the fields evaluating seed crop health. One of the things they check for is BRR. Since the disease can be symptomless it is sometimes impossible to detect. Infected potatoes, unfortunately, can slip through the cracks.
“Bacterial ring rot is stealthy,” Westra said. “It’s very good at hiding.”
“When it was first described in North America, it threatened the whole industry,” he said. “If we’d not done anything about it there probably wouldn’t be a potato industry. So we’ve gone from a total calamity to imposing that zero tolerance in seed and so now we’ve got this down to a flare-up every 10 or so years.”
In previous decades a flare-up might not have been a big deal because farms were smaller.
“Now the industry is consolidated. So we have bigger seed growers with bigger seed potato lots, selling to bigger customers,” Westra said. “Now, when it happens, it might only be a single seed lot, but the economic impact could be in the millions of dollars because everything is just so much bigger than it used to be 20 or 30 years ago.”
Under the new rule changes, all seed lots are lab tested for BRR – an added cost that growers must shoulder. Field inspections have been tightened up, too, Westra said. Basically, if the inspector stops in the field to look at what they think is potentially a problem, it must immediately be sent in for testing.
“The whole idea behind the testing program right now is to demonstrate that our seed farms in the state here are clean, that our program as a whole is clean, and to reassure the industry that we’re on top of this and restore the confidence in seed potatoes being free from ring rot,” Westra said.
In North Dakota, Gudmestad and his colleagues have recently received federal funding for postharvest testing of the disease. “We do that for a lot of other pathogens. The problem is that the methodology that’s currently used involves sampling tubers – it’s quite a few you have to sample,” Gudmestad said. “You have to test like 4,600 of them. It gets very expensive and so my colleagues and I are looking at developing an in-season test that can be used to screen potatoes during the growing season in the field as opposed to harvesting tubers and sending them off to a lab, which is very expensive just in the shipment alone.”
Although the in-season test isn’t ready this year, the results have been promising, he said.
The second project the team is working on is evaluating specialty potatoes.
“Most of those have come from Europe,” he said. “They’re Dutch varieties, they’re English varieties, they’re German varieties… and because they supposedly don’t have ring rot in Europe anymore, those have never been tested for their ability to express bacterial ring rot.”
The team is now evaluating those varieties for BRR, as well.
“After two years of testing, we have five varieties that we know have high population of the ring rot bacterium in the plant, but we’ve never seen them express any symptoms,” Gudmestad said. “But it’s there.”
“Those kinds of scenarios might very well be where we have a reservoir of ring rot that could be contributing to our inability to get rid of the problem,” he said. “Some states have more specialty potatoes certified in their system than others. “Those states tend to be the ones also having more of a problem, just in my casual observation. If this turns out to be true, then we are going to have to, as an industry, look at the seed certification policies and probably mandate that varieties that are known not to express bacterial ring rot have to be postharvest tested in order to find the bacterium.”
