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Rice researchers breeding for multi-race blast resistance

California rice growers have two blast resistant varieties to choose from, the latest being M-208, released commercially to growers last season.

M-208 is an early maturing, semi-dwarf, Calrose medium grain rice variety that has gene resistance to the only blast race found in California, IG-1.

However, Jeff Oster, California Cooperative Rice Research Foundation plant pathologist, told those at the recent Rice Experiment Station annual rice field day in Biggs, Calif., that history tells plant pathologists that resistance to one blast gene, while effective, can be a short-lived solution.

That is why the foundation is funding a rapid backcross program to incorporate more than one gene for resistance and other forms of resistance to avoid this problem.

This disease-resistance breeding uses only non-adapted varieties and is very time consuming, Oster explains.

That is why the station is setting up a molecular marker-aided selection lab to identify other genes and develop resistant varieties quicker. “This would allow screening for resistance without the presence of the fungus. It would also allow detection of more than one resistance gene in a single variety, which is not possible by screening with the one race now present in California,” the pathologist explained.

Varieties selected for this rapid backcrossing work were imported from the International Rice Research Institute in the Philippines and other rice-producing areas of the world. Five of the six targeted backcrosses have been completed, said Oster. Within the next six months, seven broad-spectrum resistance genes will be transferred into an M-206 background.

“Resistance genes will then be stacked to prevent the blast pathogen from overcoming the major gene resistance so easily,” he said. With the aid of the new molecular marker process available at the Biggs station, this stacking technique should be accomplished in two years.

A similar, immediate backcross program has been started to transfer stem rot resistance from exotic varieties to a medium grain California rice variety. Oster said plant breeders have successfully bred stem rot resistance into long and short grain California rice varieties, but not medium grain.

A similar program is being used to develop sheath blight resistance, which is similar to sheath spot disease found in California.

Hopefully, this breeding work will be as successful as the program to minimize bakanae disease, first discovered in California about eight years ago. The disease spread quickly throughout California, but just as quickly it has been turned back over during the past four years. Since 2003, less than one percent of seedlings have been affected by bakanae.

Since this disease is seed-borne, the most effective means of control is the use of non-infected seed.

“Using bleach as a seed treatment can greatly reduce seed lot infestations,” he explained. Rice researchers have found that soaking seed for 2 hours in a premixed solution of 5 gallons of sodium hypochlorite (Ultra Clorox Germicidal Bleach) to 100 gallons of water, then drained and soaked in fresh water virtually eliminates any chance of the disease in the planting seed.

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