Figure 1. Cross section of tubers with BRR infection showing complete deterioration of the vascular tissues. Photo courtesy of UI.
Figure 2. Cross section of tuber being squeezed to express the bacteria in the vascular tissues. Photo courtesy of UI.
As we go forward into the harvest season and whirlwind of activities that this hectic time of year entails, many of you may have forgotten about an important potato disease that often begins to show up during harvest. The disease is bacterial ring rot (BRR). We are currently doing our best to eliminate this disease from potato production not only in Idaho but throughout the rest of North America.
One of the most important activities in this crusade involves identifying the disease when and where it occurs and taking measures to eliminate it from affected farming operations. Something else the industry is doing that has not been attempted on a large scale before is the use of real-time PCR to test seed lots for BRR before planting.
Bacterial Ring Rot (BRR) may begin showing up in affected fields during and even before harvest.
The foliar symptom is a wilt that will become more and more difficult to differentiate from other types of wilt as the season draws to an end. Tuber symptoms range from a slightly yellow discoloration of a portion of the vascular tissues to the complete deterioration of the vascular ring (Figure 1).
Secondary invaders such as bacterial soft rot can rot out the entire center portion of the tuber, leaving behind a hollow shell consisting only of the intact tissues from the vascular ring outward. Surface cracking on tubers is frequently observed as well but not always. In both infected stems and infected tubers, the vascular tissues become clogged with large numbers of the BRR bacterium and squeezing the tuber or stem to look for "bacterial ooze" is a field diagnostic technique that is used routinely (Figure 2).
We are encouraging any growers or consultants who find samples that they suspect are BRR to bring these samples to University of Idaho personnel for further testing. You should contact Phillip Nolte at Idaho Falls (208) 529-8376, Nora Olsen at Kimberly (208) 423-6634 or Mike Thornton at Parma (208) 722-6701. Please do not bring any suspected BRR samples to the Aberdeen or Tetonia stations! Upon confirmation of a BRR-positive sample, we will follow up with information on how to properly clean up and disinfect the affected farming operation to avoid future self-inflicted outbreaks of the disease in those operations.
For seed testing, the Idaho Crop Improvement Association Laboratory in Idaho Falls, with the combined help of several concerned companies from both the processing and fresh potato industry, has purchased a real-time PCR machine to perform BRR testing. Many growers will elect to have their seed lots tested due to contract conditions that limit the amount of BRR their buyers will allow into their packing or processing facilities. We would encourage anyone who has concerns about the BRR status of seed they are considering for planting to have the seed tested. You can arrange for testing by calling Sherry Laug (ICIA) at (208) 522-9198. There are several other labs around the country that can perform this testing, including the diagnostic lab at North Dakota State University in Fargo and Agdia's lab in Indiana among others.
Dr. Neil Gudmestad from NDSU, Dr. Jonathan Whitworth from the USDA-ARS breeding project in Aberdeen and I, Phil Nolte, University of Idaho in Idaho Falls, recently received an NPC grant to perform research on BRR. Our work will focus on improved detection using PCR methods, but we will also be determining the BRR reaction of new varieties. This is important because growers and certification officials need to know whether or not these varieties express symptoms, what the symptoms look like and when they begin showing up in the field. This information will help the certification people to do a better job of recognizing the disease in these newer varieties.