ARS Releases Iceberg Lettuce Breeding Lines Resistant to
Bacterial Leaf Spot
April 13, 2009
Seven new iceberg lettuce breeding
lines with resistance to bacterial leaf spot (BLS) have been released by
Agricultural Research Service (ARS)
BLS, caused by the pathogen Xanthomonas campestris pv. vitians, is an
important disease of lettuce in California. Iceberg lettuce is the most popular
type of lettuce eaten in America. Nearly all of the lettuce consumed in the
United States is produced domestically. Two states, California and Arizona,
produce more than 90 percent of the country's commercial lettuce.
Occurring on both leaf and head lettuce varieties, BLS thrives in wet, cool
conditions. It is most serious in early spring and late fall, when it is most
likely to rain in California. BLS causes black spots to form on lettuce leaves.
These black spots can merge and create papery, brown-to-black patches on the
head. Upon harvest, farmers must peel and discard the leaves to remove the
patches, resulting in smaller heads that command less money.
BLS is difficult to prevent because the disease is highly dependent on
weather conditions. Farmers can spray their lettuce crops with pesticides, but
the chemicals have to be applied before symptoms develop, which is impractical.
Because BLS is sporadic and unpredictable, these preemptive sprayings would be
unnecessary in most seasons and lead to increased production costs. Therefore,
according to ARS geneticist
Hayes, creating disease-resistant breeding lines is the most efficient and
cost-effective tool to manage BLS in lettuce.
Hayes, along with geneticist Edward Ryder (now retired) and plant
Bull, developed the seven new breeding lines at the
Crop Improvement and Protection Research Unit in Salinas, Calif. Similar in
appearance to the famous ?Salinas' variety created by Ryder, these lines are
the first western shipping-type icebergs with commercially useful levels of
resistance to BLS. ARS provides these lines to seed companies, which in turn
use them to develop new iceberg varieties for commercial use.
Limited samples of seed from these breeding lines are available from the ARS
unit in Salinas to researchers and seed companies.
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.