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Rice Researchers Fight Straighthead Disease and Improve Grain Quality

By Jim Core
October 28, 2005

Rice breeding lines that resist a costly disease, as well as lines with desirable grain characteristics, have been identified by Agricultural Research Service (ARS) scientists in Arkansas.

Wengui Yan, a research geneticist at the ARS Dale Bumpers National Rice Research Center in Stuttgart, Ark., leads efforts to analyze the U.S. Department of Agriculture (USDA) Rice Core Collection. With 1,791 entries, this genebank has been estimated to contain more than 70 percent of the genetic variation in the National Small Grains Collection's 18,408 rice accessions.

Utilizing the core collection, Yan and his ARS colleagues identified germplasm accessions that are very resistant, or even immune, to straighthead, a plant disease that causes the entire rice head to remain upright at maturity with sterile florets and reduced grain yield.

There is no straighthead resistance in commercial U.S. rice cultivars, but Yan has identified 26 indica and japonica rice lines that are resistant. Breeders at the University of Arkansas and Louisiana State University have incorporated some of these germplasm lines into their programs.

Straighthead yield losses can reach almost 100 percent if a highly susceptible variety is planted in the wrong conditions. The germplasm recently discovered to be resistant is diverse in origin, maturity and plant height. According to Yan, it can be used to improve straighthead resistance in rice breeding in the southern United States.

Stuttgart researchers are also addressing undesirable amylose content levels in indica rice. Amylose content is the characteristic used to describe the difference between dry, flaky rice (which indicates a high amylose content, typical for U.S. long grain rice) and moist, sticky rice (which indicates a low amylose content, typical for U.S. medium grain rice).

Germplasm of foreign indica rice, the principal type grown worldwide, usually has higher grain yields than U.S. cultivars. However, it is considered to have poorer grain quality.

Through hybridization and induced mutation breeding, J. Neil Rutger, a lead ARS scientist in Stuttgart, and Yan have developed numerous indica lines with ideal amylose content for the U.S. rice industry.

ARS is the USDA's chief in-house scientific research agency.