Cause of bean spot baffles experts

It’s nice to find a simple cause and a simple solution to a crop disease, but with cranberry bean marsh spot that’s probably not going to happen.

Instead, researchers are reaching toward an understanding and building a complex response.

“There’s a big environmental component to this disease,” said Bob Conner, an Agriculture Canada researcher at the research centre in Morden, Man. “It’s probably a little more complex than just being one micronutrient.”

Cranberry bean marsh spot isn’t easily visible in the field, but it leaves an obvious mark in the middle of beans.

“You don’t really know you have a problem until the seeds are split,” said Conner.

Because people don’t want to eat it, processors generally won’t buy affected beans, even though marsh spot is not a health concern. The disease is also believed to affect germination rate and seedling vigour.

Cranberry bean marsh spot is not caused by a pathogen, a type of parasitic life form. It is more similar to a health condition.

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But researchers don’t know what causes it.

At one point, they thought it was caused by manganese deficiency, but tests showed mixed results, with no definite cause and effect.

A similar disease that appears in peas is caused by manganese deficiency.

Researchers are trying to develop resistant varieties, but aren’t focused on a particular gene or genetic solution.

Some varieties have high susceptibility, while others are only slightly vulnerable to the disease. Researchers at Morden and elsewhere have been combining the best commercial types with the most resistant types.

Most say that creating resistant varieties that are also commercially valuable is possible.

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