For onion growers battling botrytis leaf blight, a crop-decimating disease, relief is on the way. Cornell University
plant scientists have breached the plant's tough sexual barrier to cross two species and develop a first draft of a botrytis-resistant onion. The way is now paved for scientists to bring the onion to commercial quality and, perhaps, make it resistant to other diseases as well.

Martha Mutschler, Cornell professor of plant breeding, will unveil her research team's results Feb. 11 at 2 p.m. at the 2004 Empire State Fruit and Vegetable Expo in the Riverside Convention Center's Bausch Room, Rochester, N.Y. Her research collaborators were Jim Lorbeer, Cornell professor of plant pathology; research associate Edward Cobb; and graduate student Pablo A. Goldschmied.

Mutschler's team obtained the resistance from A. roylei, a wild plant species related to the onion and held at the U.S. Department of Agriculture's germ plasm cold-storage facility at Fort Collins, Colorado. She describes this rock-garden plant as a "treasure trove of resistances." The major obstacle was breaking down the onion's sexual
barriers to cross the two species. Strong sexual barriers reduced the onion plant's fertility and seed quantity. "Without seeds, a breeding program is stuck," she says.

In 2001 Mutschler and her colleagues concentrated on obtaining seed from botrytis- resistant back-cross plants, their progeny and other resistant plants, but sexual barriers limited seed production from zero to 20 seeds per plant. However, three back-crossed plants produced more than 100 seeds. "This segregation for superior seed production shows that the sexual barriers are under genetic control and that fecundity is probably a recessive trait derived from the onion parent," she says.

By the summer of 2002, more than half of the back-crossed plants yielded resistance, and more than 94 percent produced onion like bulbs.

Last spring a total of 112 resistant onion plants sprouted. Mutschler says bulbs were retested for botrytis resistance, evaluated for pollen production and used in seed production. About 20 of the botrytis-resistant, back-crossed plants had adequate pollen fertility and produced good seed levels.

"To put these results in perspective, we produced considerably more seed from botrytis- resistant plants in one year than we had produced in all prior years on the project combined," says Mutschler. "This is evidence that the inter-specific barriers between onions and A. roylei have been fully overcome in some of our selections and that completion of the transfer of the dominant botrytis resistance to the onion should proceed far more readily."

The seed will be grown in 2004 and screened for resistance. Mutschler says that with greater availability of seed, greater selection for plant type also should be possible, accelerating completion of the transfer. Over the next growing season, she hopes to improve the onion's firmness, size and number of centers. Botrytis-resistant onions could be ready within a few years.

The research was funded by the New York State Onion Growers Association's check-off program, administered through the New York State Department of Agriculture and Markets.