Zebra chip discovery in Pacific Northwest spuds raises questions

11/18/2011 05:58:00 PM
Vicky Boyd

Until this year, no zebra chip had been reported in the Pacific Northwest.

“Why this year the psyllids are hot, I don’t know,” Munyaneza says.

Psyllids overwinter and reproduce in northern Mexico and the desert Southwest.

Starting in late spring, they migrate north on the wind as temperatures warm.

Munyaneza theorizes that psyllids also migrate into the Pacific Northwest annually and don’t overwinter. If they did spend the winter, he says he’d expect to begin catching them in April when the potatoes emerge.

One of the questions Munyaneza says he hopes to answer by examining psyllid DNA is from where they are originating. Are they moving up from California or from Texas?

“My lab is trying to connect the dots and trying to trace the origin of the insects,” Munyaneza says.

Once the origin is known, then researchers can monitor psyllids in that region to try to predict insect and zebra chip outbreaks elsewhere.

Read about the 2010 potato psyllid season and how growers learned from it by clicking here.

The psyllid-zebra chip connection

Zebra chip gets its name when the Candidatus Liberibacter organism causes part of the starch in the tubers to convert to soluble sugar. As the potatoes are cooked—such as during chip frying—the sugar caramelizes, forming undesirable dark, zebra-like stripes.

The discoloration is harmless to humans or animals but renders the potato product unmarketable.

Potato psyllids spread Liberibacter as they feed, but only a small percentage of psyllids actually carry the pathogen.

As few as one psyllid per plant is enough to cause zebra chip, according to research conducted by Joe munyaneza, a research entomologist with the Agricultural research Service in Wapato, Wash.

Infected plants in the field die over a period of several weeks. vines of infected plants are yellow and may have swollen nodes, aerial tubers, axial bud elongation and wilting.

These are similar to foliage symptoms associated with psyllid yellows, which can affect tuber production but doesn’t affect internal tuber quality. It is probably caused by the saliva toxin the nymphs, or immature psyllids, inject during feeding.

Zebra chip was first confirmed in mexico in 1994 and in the United States in Texas in 2000. It has since been found in Kansas, Nebraska, New Mexico, california, Arizona, Wyoming, colorado and recently in Idaho, Washington and Oregon.

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