Resistance Offers Best Solution For Rice Diseases

Donald Groth, Schultz, Bruce, Rush, Milton C.  |  12/15/2006 12:54:29 AM

News Release Distributed 12/14/06

Developing disease-resistant varieties is the best approach to help farmers fight diseases that afflict rice, said Don Groth, LSU AgCenter plant pathologist at the Rice Research Station in Crowley.

"That’s been our primary objective from the beginning," he said. "It’s more effective in the field."

The two main diseases that hurt Louisiana rice production are "blast" and "sheath blight." If these diseases break out in a field, the treatments with fungicides can get expensive, Groth said.

Funding from the Louisiana Rice Research Board is being used to develop resistant varieties, he said. That process has been improved by using genetic markers to identify disease-resistant genes of potential varieties, he said.

"It’s making evaluation much easier," he said. "Right now, we can screen for blast resistance, and we’re close to having markers for sheath blight resistance."

Developing a variety with total immunity from disease is not feasible, Groth said. That’s because a plant that uses its energy toward warding off disease will often have a low yield potential, he said. The secret is obtaining the right match of genetic resistance and inherent yield potential.

Blast has the capability of destroying an entire crop, and sheath blight losses can amount to 25 percent.

"We have not had a bad blast year in seven to eight years," Groth said.

Individual rice fields have blast problems, Groth said, but it is not widespread. Nevertheless, he said the likelihood exists that blast eventually will adapt to current rice varieties, causing an outbreak.

Blast has become more of a problem for the Cypress rice variety, introduced by the LSU AgCenter in 1992, although in its first few years that was not the case. It is not that the variety becomes more susceptible, but that the disease organism begins to adapt to be more damaging.

This year, narrow brown spot caused by the fungus cercospora has plagued many fields. Groth said it usually doesn’t become a problem until a second crop of rice is grown.

"It’s probably one of the worst diseases we see in the second crop," he said.

Work is under way with screening for disease resistance and fungicide experiments, funded by the Rice Research Board, to help farmers.

"We will have data this year, and we will have a pretty good idea on best control methods for next year," Groth said.

Bacterial panicle blight is an important disease that is more of a problem in certain years and under certain environments. With funding from the Rice Research Board, work is progressing on a screening for disease resistance to this seed-borne disease.

Chuck Rush, LSU AgCenter pathologist, said Rice Research Board funding helped the discovery in 1996 that panicle blight is actually caused by a pathogenic bacterium. Some chemicals are being tested as seed treatments against the disease, he said, and six sources of partial resistance to bacterial panicle blight have been identified.

Several lines have been developed with resistance against the bacterium by crossing resistance sources with commercial varieties.

Bacterial panicle blight can cause losses of 500-600 pounds per acre without a farmer knowing his field has been afflicted, Rush said.

The disease thrives during unusually warm nights, he said, recalling that the worst years for bacterial panicle blight were during the heat waves of 1995, 1998 and 2000.

Rush said after years of making crosses, the breeding program has several lines with good disease resistance, including sheath blight resistance and the potential to be varieties.

"We have generated a large number of lines with partial resistance to sheath blight," he said. "A good number have performed well, and we are getting to the point in our yield tests where we have lines that out-yield commercial varieties."

Groth said he was the first full-time pathologist at the Rice Research Station when he started his career in 1984. Rice Research Board funding provided equipment, a vehicle and personnel to conduct his research. As state budget cuts became more frequent, the board’s funds helped reduce that impact, he said. Rice Research Board funds have also been needed to do work on fungicides because chemical manufacturers are sometimes unwilling to pay for work that would affect rates and timing of applications, he said.

The Rice Research Board gets most of its funding through a check-off program for rice farmers. This program is up for renewal, and a referendum will be held Jan. 30, 2007. If approved, the check-off amount would remain at 5 cents per hundredweight for the next five years. The self-assessed fee has been continuously approved since it was first approved in 1972.


Don Groth at (337) 788-7531, or
Chuck Rush at (225) 578-1393, or
Bruce Schultz at (337) 788-8821, or

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