Strides Made In Bacterial Leaf Spot-Resistant Lettuce

By Growing Produce Staff|April 15, 2009

Seven new iceberg lettuce breeding lines with resistance to bacterial leaf spot (BLS) have been released by USDA-Agricultural Research Service (ARS) scientists. 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 U.S. is produced domestically. Two states, California and Arizona, produce more than 90% 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. Growers 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 Ryan 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 pathologist Carolee Bull, developed the seven new breeding lines at the ARS Crop Improvement and Protection Research Unit in Salinas, CA. 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.