March 2011
Improving Seed Performance By Bill Schaefer

To cut, or not to cut, that is the question facing many growers as they make their planting preparations. How you prepare and treat your seed stock at planting time are factors that play crucial role in the overall health of your crop and your eventual success at harvest time.

Unlike beans, corn or wheat in which you plant a true, hard seed, potato seed is really just a vegetative clone. True seed comes with a seed coat, a protective barrier to all kinds of pathogens that cannot penetrate the seed coat to infect the nutrients or the embryo. Seed potato tubers, on the other hand are generations removed from their origin as true seed.

Phil Nolte, University of Idaho Extension professor and seed potato specialist, knows that potato growers face a lot of tough decisions when it comes time to plant and he predicates any additional advice for growers with this caveat:

“Certified seed, with all the care it receives, is absolutely necessary,” Nolte said.

Nolte, along with Amy Charkowski, University of Wisconsin at Madison seed specialist and director of the Wisconsin Seed Potato Program, and Jonathan Whitworth, research plant pathologist at the USDA Agricultural Research Station in Aberdeen, Idaho, presented on seed potato performance at the 2011 University of Idaho Potato Conference.

All three began their individual presentations by advocating that growers use only certified seed in their operations.

Nolte’s presentation focused on how to maintain healthy seed after it’s been cut. North American growers generally cut seed tubers to create seed pieces, whereas in Europe and some areas of the United Staes they use whole seed, also called single drop seed, Nolte said.

Cut and uncut seed present their own set of advantages to growers.

Advantages to using whole seed include:

  1. high vigor
  2. increased stem counts
  3. increased tuber set
  4. tuber size tends to be uniform due to heavier set
  5. less disease.

The advantages to using cut seed include:

  1. reduce cost by extending your seed stock to meet acreage demands
  2. smaller, more uniform seed pieces
  3. less stem counts, smaller set and larger tubers.

Generally, in the United States, growers use cut seed and that creates a litany of potential problems for the health of the seed piece.

When you cut the potato seed you’ve created an open wound, an area that gives all kinds of pathogens unimpeded access to the potato. Soft rot and fusarium dry rot are the two major diseases affecting cut seed potatoes.

After cutting seed you want the wound to heal to prevent these pathogens from infecting your seed stock.

Suberization is a process that creates a protective seal over the wound protecting it from infection.

It’s a kind of corky substance that forms over the cut.

“At this point in time, about 48 hours after the seed has been cut, that suberin barrier will probably stop soft rot but it won’t stop dry rot. You have to have five or six days of healing before you get proof against fusarium,” Nolte said.

It takes between 14 and 21 days to form a permanent wound barrier.

“I recommend using seed piece treatment for cut and healed seed for several reasons,” Nolte said.

Advantages include dry rot and late blight prevention as well as management of silver scurf and rhizoctonia. In addition seed treatments change the environment at the seed piece surface, they soak up sap preventing pieces from sticking together and preventing anaerobic conditions, thereby encouraging better movement of air among the seed pieces.

Nolte said that placing the cut seed back into storage slows the healing process down.

“We usually recommend temperatures at 50° F to 55° F for suberization. Favorable temperatures are a compromise. Warm enough to let wound healing take place and cool enough to keep pathogens from getting out of hand,” Nolte said.

“This is an aerobic process, it needs oxygen. If stuff is piled too deep there may be places that aren’t getting adequate oxygen and that will stop the process (suberization) from taking place,” he said.

Nolte said that you want to maintain a relative high humidity of 90 perecnt to 95 percent.

“If you have a marginal storage facility you may be best advised to just cut it and plant it,” he said.

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