Ithaca, New York
February 9, 2004
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
By the summer of 2002, more than half of the back-crossed plants
yielded resistance, and more than 94 percent produced onion like
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
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
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.