Potato diseases may lurk on imported tulip bulbs

NIAGARA FALLS, Ont. — It’s bad enough that the disease that causes blackleg in potatoes and carrots, Pectobacterium, is widespread in North America.

Now two closely related anaerobic bacterial diseases, more virulent in nature, pose an added threat.

Vikram Bisht, a plant pathologist with Manitoba Agriculture, said Dickeya dianthicola has already found its way to North America from Europe. Dickeya solani, which is commonly isolated from seed tubers in the Netherlands, could do the same.

“We import a lot of flower bulbs from Holland. You just need one bulb out of a million that’s infected and has favourable weather conditions, and then we have an issue,” he told the Ontario Fruit and Vegetable Convention in Niagara Falls Feb. 22.

“There’s a risk, but I won’t say it’s being exported without checks.”

Few if any Dutch tubers find their way to North America, but flower bulbs do. Bisht cited a peer-reviewed paper written by Scottish researcher Ian Toth showing these can carry the disease.

Dickeya dianthicola has been identified in Maine, a major producer of seed potatoes in North America, and other U.S. locations. There’s also a report of it being found in a commercial field of processing potatoes in Ontario.

In Israel, losses of up to 25 percent have been attributed to Dickeya infections.

Bisht emphasized the importance of obtaining clean seed. Unfortunately, the testing procedures for seed are expensive and flawed. Not all the seed tubers in lots are evaluated under existing protocols.

For example, he said that when tests in the Netherlands find no Dickeya or Pectobacterium, there’s a three to four percent chance of blackleg developing the following year in the field where they are planted.

Blackleg is the term used to describe damage caused by the several Pectobacterium species, but the same type of symptoms can develop with a Dickeya infection. That includes plants dying because of damage to their vascular system.

An important difference between Pectobacterium and Dickeya is that Dickeya species thrive under warmer temperatures.

Infected tubers placed in storage can develop soft rot, especially if storage protocols are poorly managed.

Bisht saw the results in one storage location last year in which both late blight and Pectobacterium were likely present.

“I was knee deep in liquid in a ventilation gutter,” he said.

“It basically makes a soup out of your potatoes in storage, especially if there’s poor air circulation.”

There are no chemical controls for Pectobacterium or Dickeya. Poorly drained fields are especially susceptible.

The best way to manage the diseases once they find their way to a field is to rotate away from potatoes and other host crops, including carrots and onions, Bisht said.

With Pectobacterium, non-host crops should be grown for at least two years after an infection is identified. With Dickeya, a one-year rotation away from host crops is recommended because the pathogen doesn’t survive well in the soil.

Climate change may be contributing to increasing insect and disease pressure, including Dickeya, in more northerly growing areas, he said.

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