Technical Abstract: The Agricultural Research Service, United States Department of Agriculture (USDA) announces the release of two breeding lines of green leaf lettuce (Lactuca sativa L.). The lines 06-831 and 06-833 look similar to ‘Waldmann’s Green’ and related cultivars. The lines may be suitable for commercial production, and are suitable for use as sources of resistance to corky root in the development of cultivars and germplasm. They were developed at the United States Agricultural Research Station in Salinas, California by Beiquan Mou. Corky root infected plants develop yellow to brown lesions on the roots and the lesions later become longitudinal corky ridges. In severely infested fields in California and Florida, yield losses from reduced head size can reach 30-70%. The breeding lines were derived from a cross between a green leaf cultivar ‘Waldmann’s Green’ and a crisphead cultivar ‘Glacier’ that has a resistant gene. The corky root disease of the breeding lines was not significantly different from ‘Glacier’, but was significantly less than nine susceptible leaf lettuce cultivars in field trials. In the limited trials grown, 06-831 and 06-833 have performed well in the Salinas Valley, Calif., producing a high percentage of plants of adequate size, shape, and uniformity. Limited samples of seed are available for distribution to all interested parties for research purposes, including the development and commercialization of new cultivars.