Understanding continues to increase

Published in the January 2009 Issue Published online: Jan 27, 2009
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Don Henne looks for potato psyllids, the insect that carries the zebra chip bacteria.

Don Henne spends a lot of time standing by a deep fryer waiting for potato slices to turn brown.

But it's not tasty snacks he's looking for. He's conducting research into zebra chip disease and he says the research team hopes to have some management suggestions on how to help alleviate the zebra chip problem for growers by the end of this year.

Henne, an assistant research scientist in the Texas AgriLife Research plant pathology program in Amarillo, is one of many trying to find answers about zebra chip, the latest disease to plague the potato industry-especially those in the chipping business.

Zebra chip alters the sugar levels in the potato. The sugar caramelizes and turns the chip brown when it is fried, giving it an off taste and burnt appearance. While it is not harmful, it is a cosmetic and taste concern for consumers.

Crops have been affected in Guatemala, Mexico, Texas and as far north as Colorado.

AgriLife Research plant pathologist and program leader Charlie Rush began working on the project at the request of local producers in early 2007. His work later became a part of the zebra chip state initiative through the Texas Department of Agriculture.

Rush says the initiative brought together researchers from throughout the state and country to try to find answers for zebra chip.

"When we first began working on it, the pathogen and vector were unknown," he says. "Only recently have researchers begun pinning those down."

Rush says Henne was brought into the program in May because of his experience and background. His primary responsibility is to help understand the factors that impact disease onset and spread.

Growers have had to abandon entire infected fields, costing as much as $2 million a year in damage.

Henne, who has a degree in entomology, is chasing the potato psyllid, the insect that likely carries the pathogens causing the disease.

He is trying to find out what makes it move through a field, as well as when it moves and how fast.

He has visited grower fields this year and has made contact with other zebra chip researchers around the U.S. to familiarize himself with this new chipping potato disease.

Zebra chip first appeared in Mexico and Guatemala in the early 2000s. It has been found in potato fields through South Texas and the Rio Grande Valley and now up into the South Plains and Panhandle regions.

Henne says the disease presents itself as curled leaves and stunted growth in the plant itself, and then the tubers exhibit a brown striped or mottled pattern when sliced.

AgriLife Research and other scientists around the country have studied the vector or insect that transmits the pathogen, he says. Others are trying to identify the pathogen or bacteria that actually cause disease in the plant when the psyllid feeds on it.

Henne and other Amarillo-based researchers are working with commercial growers to monitor the movement of the insect and disease appearance. At the same time, they have established potato plots at the Texas AgriLife Research Station at Bushland and are doing some greenhouse work.

"We're focusing on the epidemiological aspects of the disease," Henne says. "We are trying to understand how the disease progresses in a potato field over time. We are looking at canopy structure, edge effect and how the insects are landing in fields and distributing the disease."

Henne and Fekede Workneh, an AgriLife Research quantitative plant disease epidemiologist, are growing six acres of potatoes at the Bushland station where they are looking at planting dates, canopy structure and insect dispersal.

Potatoes are planted in late March to early June in the Panhandle, so they are experimenting with planting dates-May 2, May 28 and June 16-to see if there is a relation between insect movement and disease severity.

"We are also working in the lab to graft diseased portions onto healthy plants to understand the movement of the disease through the plant," Henne says.

"We want to understand how the disease progresses so we can focus management practices on specific areas," he said. "Do the insects move up the plant, down or out from the stem? Some varieties have more canopy than others and is that acting as a natural bridge for insect movement?"

There is no adequate control for the insect or the disease at this time, he says.

Because there are other diseases that have similar symptoms as zebra chip, one of the challenges researchers face is being able to correctly identify diseased plants in the field.

"When we find plants that appear to be infected, we bring the tubers back to the lab where they are sliced and fried to make the final determination," he says.