Sunflowers to Resist Parasitic Plant

An exotic weed, broomrape, so far hasn’t threatened U.S. sunflowers. But if quarantine efforts ever fail to keep out the weed, scientists with USDA’s Agricultural Research Service are tapping into genetically diverse sunflower relatives for backup protection.

Broomrape, Orobanchecumana, ranges from pink, orange-red, purple to tan depending on its environment. It’s a parasitic plant that has no chlorophyll of its own, meaning it can’t capture the sun’s energy and make its own food. Instead, it steals nourishment from sunflower roots, stunting or killing its host. Presently, it infests sunflower crops in China and countries bordering the Mediterranean and Black Seas.

As new broomrape races evolve, international researchers, in customary treadmill fashion, develop new sunflower lines with resistance genes. But ARS scientists at Fargo, N.D., and their colleagues in el Instituto de Agricultura Sostenible CSIC, in Cordoba, Spain, have developed technology called interspecific hybridization for sunflowers to avoid such “treadmills.” Interspecific hybrids are crosses between cultivated sunflowers and their distant relatives that were until now difficult--if even possible--to cross. Some, nearly ready for release to the seed industry, are not just resistant but immune to the broomrape race F, the newest race.

Broomrape became a progressively worse problem in Spain in the early 1990's. Yields of sunflowers that were susceptible to races E and F often fell by 40 to 50 percent. Urgently, ARS and Spanish scientists conventionally derived seven new resistant sunflower germplasms by crossing between USDA lines and race E-resistant lines from Russia, Romania and Turkey. New conventional hybrids from these lines are being grown in Spain where they suffer yield losses of only 10 to 15 percent. And researchers are finding that some individual plants from the seven parental lines are resistant to race F.

ARS is USDA's chief research agency.

Scientific contact: Chao C. Jan and Jerry F. Miller, ARS Oilseeds Research, Red River Valley Agricultural Research Center, Fargo, ND, phone (701) 239-1319 (Jan), (701) 239-1321 (Miller); fax (701) 239-1349, [email protected], [email protected].