Corky root of lettuce (Lactuca sativa L.) has been found in major lettuce-producing regions of the world, including North America, Western Europe, Australia, and New Zealand. Roots of infected plants develop yellow to brown lesions that later become longitudinal corky ridges. Yield losses from reduced head size can reach 30% to 70% in severely infested fields in California and Florida (van Bruggen, 1997). The pathogen most commonly isolated from diseased roots is the bacterium Sphingomonas suberifaciens (Yabuuchi et al., 1999), formerly Rhizomonas suberifaciens, although several other bacterial species have also been isolated (van Bruggen, 1997). The incidence of corky root can be reduced by soil fumigation (O’Brien and van Bruggen, 1990) and by using lettuce transplants instead of directseeding (van Bruggen and Rubatzky, 1992). However, these practices may not be economically feasible for the Salinas Valley, CA, the major lettuce production area in the United States (Patterson et al., 1986). The use of cultivars resistant to S. suberifaciens has been an important management strategy for corky root. The resistance to corky root is controlled by a recessive allele (cor) at a single locus (Brown and Michelmore,1988), which has been deployed in most resistant lettuce cultivars. Although corky root resistance has been transferred into many crisphead lettuce cultivars, there are few leaf lettuce varieties with the resistance, especially for publicly released cultivars. With increasing consumption and production of leaf lettuce, there is a need for public germplasm that facilitates the research and development of new cultivars and germplasm. In this article, we describe two green leaf breeding lines with resistance to corky root and adaptation to the major lettuce production areas of the central coast of California. Origin