Lettuce With Corky Root Resistance

The Agricultural Research Service (ARS) has released three new leaf lettuce breeding lines with resistance to corky root. A disease of lettuce, corky root is caused by a bacterium called Sphingomonas suberifaciens. The bacterium lives in the soil and feeds on the plant’s roots, causing the roots to enlarge and develop yellow to brown lesions and longitudinal cracks, taking on a cork-like appearance.

Once infected, the roots are unable to effectively absorb water and nutrients, resulting in smaller lettuce heads and yield loss. Because cultural practices and fumigation techniques used to treat the disease are costly and labor-intensive, the development of lines with genetic resistance is still the optimal way to combat the disease. Additionally, growers have increased production of this type of lettuce, further highlighting the need for leaf lettuces with resistance to corky root.

The three leaf lettuce breeding lines were developed by ARS geneticist Beiquan Mou. The disease-resistant lines include one red leaf lettuce and two green leaf lettuces. This follows his and colleagues’ previous work in developing corky-root-resistant iceberg lettuces. Mou crossed disease-resistant iceberg lettuce Glacier with popular leaf lettuce varieties. The offspring were tested at the ARS Crop Improvement and Protection Research Unit’s research farm in Salinas, CA.

The new breeding lines are the latest to be released by the Salinas lab. Their plant weight is comparable to or higher than commercial cultivars. The breeding lines also showed little to no tipburn in test trials.


The adaptation of these breeding lines to other lettuce-growing regions has not been evaluated. However, leaf lettuce has less environmental requirements than iceberg lettuce, allowing leaf lettuce to adapt to a wider geographical area. The new lines can be used commercially for production of fresh lettuce or to develop new cultivars.

Source: ARS news report

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