New Lettuce Lines Offer Improved Shelflife, Disease Resistance

In an effort to control economic losses to California and Arizona’s vital lettuce industry, scientists are being challenged to develop new Romaine lettuce breeding lines that provide genetic resistance to dieback, a disease indicated by symptoms including mottling, yellowing, and death of older leaves, and stunting and eventual death of lettuce plants. Dieback disease, caused by two soilborne viruses, affects romaine and leaf-type lettuce, often leading to crop loss of 60% or more.


Add in another challenge for researchers: some recently developed Romaine cultivars that are resistant to dieback have limited shelflife, decaying quickly when processed for salad. Three Romaine-type breeding lines with resistance to the disease were previously released by USDA’s Agricultural Research Service (ARS) in Salinas, CA. Now, the Salinas breeding program has introduced new romaine breeding lines that prove praiseworthy in terms of both disease resistance and shelflife. Ivan Simko and Ryan J. Hayes from the USDA-ARS in Salinas, Krishna V. Subbarao of the Department of Plant Pathology at the University of California, and Rebecca Grube from the University of New Hampshire introduced the new romaine lines in a recent issue of HortScience.

SM09A and SM09B are F8 Romaine breeding lines of lettuce (Lactuca sativa L.) resistant to the dieback disease and with good shelflife. SM09B was selected from a cross between ‘Darkland’ and PI 491224. SM09A was developed from ‘Green Towers’ (‘Darkland’ x PI 491224). “In replicated field trials, the two breeding lines showed complete resistance to dieback. Testing of salad-cut lettuce in modified atmosphere packaging indicated slower decay in the two breeding lines compared with other dieback-resistant romaine varieties,” noted Simko.

Limited samples of seeds are available for distribution for research purposes, including the development and commercialization of new cultivars. Samples are deposited in the National Plant Germplasm System under numbers PI 658678 and PI 658679. Address written requests to Simko at [email protected].

The complete study and abstract are available on the ASHS HortScience electronic journal web site:

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