Sugar beet virus mutation requires Texas touch

05/17/05

AMARILLO – The only sugar beets growing in Texas are in the laboratory. But those few plants are getting to the root of problems throughout the sugar beet industry.

The sugar beet industry moved out of Texas in 1997 after the close of the processing plant at Hereford. But the growing research program within Texas Agricultural Experiment Station's plant pathology lab here didn't die.

Just the opposite, said Dr. Charlie Rush, professor and director of the plant pathology labs in Bushland and Amarillo.

"We do all of our work in the greenhouse and laboratory," he said. "Here, we have to have an understanding of everything, from the crop growing in the field to the molecular aspects of the pathogen. That makes our program totally unique."

Outside research dollars began pouring in and Rush's program was reinvigorated in 2002 when a new strain of beet necrotic yellow vein virus emerged.

The new strain threatened sugar beet production in California and Minnesota. Getting answers was important because the affected area in California holds records for production and Minnesota boasts the most concentrated sugar beet growing region in the world, Rush said.

Beet necrotic yellow vein virus, which causes the disease known as rhizomania, was found near Hereford in 1986 by a California researcher. A similar virus, beet soil borne mosaic virus, also was found about the same time.

The two viruses are closely related, Rush said. But rhizomania is devastating and found worldwide, while the mosaic virus is not as destructive and is limited to the United States.

Growers, breeders and industry officials from Colorado, Nebraska, Wyoming, Idaho, Minnesota, Michigan and North Dakota began looking to Texas and Rush for help.

They would see rhizomania in isolated spots in a few fields, but within a few years, it would spread across entire production areas, Rush said. His team responded by studying the ecological and epidemiological aspects of the pathogen and disease – what could producers do to reduce the incidence and severity of the disease.

"We started doing a lot of work with both of the viruses, and by default, I ended up with more experience than anyone else," he said. Strong genetic resistance to rhizomania was bred into sugar beet varieties and until 2002, that was effective, Rush said. But with only one gene selected for resistance, the plant virus mutated and overcame the resistant gene.

"We're going in now and looking at the molecular makeup of the plant virus," he said.

Making trips to the Imperial Valley in California and the Red River Valley growing region in Minnesota and North Dakota, Rush said his team works with growers and sugar company representatives at harvest time.

Soil samples and infected beets are brought back to the lab at Bushland. Sugar beets are planted in the contaminated soil and the virus is purified from the infected plants, he said. The virus isolate is cultured in test tubes, and the plants are no longer needed.

"We're trying to find out why this genetically mutated pathogen is able to overcome the resistance in the plant," he said. "We're looking at new crosses by seed companies and challenging them with each of these two viruses, as well as a combination of the two."

By measuring the effect of the disease on the plant, as well as purifying the virus and quantifying how much is actually present, they can determine if resistance is expressing itself, Rush said.

Breeders have good indications they may have some resistance in some wild relatives of sugar beets, he said. Advanced lines identified with potentially high levels of resistance will be planted in test plots in the sugar beet growing regions.

When these lines become available to producers and allow them to grow beets at a profit, that's when the research has come full circle, Rush said.

Source: Eurekalert & others

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