2005 Annual Report 4d.Progress report. This report serves to document research conducted under a trust fund between ARS and the California lettuce Research Board. Additional details of research can be found in report for in-house project 5305-21000-011-00D, Evaluation, Enhancement, Genetics, and Breeding of Lettuce, Melons and Closely Related Species. Our objectives are to incorporate resistance to several diseases and insects into crisphead and mixed lettuce cultivars and breeding lines. In FY2004/2005, major efforts targeted resistance to lettuce big vein disease, downy mildew/Bremia, lettuce drop/Sclerotinia minor, Verticillium wilt, Fusarium root rot, lettuce mosaic virus, lettuce dieback/tombusviruses, bacterial leaf spot, corky root, leafminer, lettuce aphid, and multiple disease resistance. Minor programs addressed adaptation to low desert conditions, nutritional content, as well as resistance to Phoma basal rot and powdery mildew. In all programs, horticultural traits, adaptation, and resistance to tipburn are considered essential. In FY2004, we identified new candidate sources of resistance to big vein disease, Verticillium wilt, and lettuce drop. We confirmed resistance of previously identified germplasm to corky root, big vein disease, powdery mildew, and lettuce aphid. Additionally, cultivars, primitive lettuce, and wild Lactuca species were evaluated for nutritional content. Advanced breeding lines were evaluated for resistances to big vein disease, lettuce mosaic virus, corky root, downy mildew, powdery mildew, bacterial leaf spot, lettuce drop, Verticillium wilt (crisphead), dieback (romaine), and tip burn. Genetic studies concurrent with breeding programs are being conducted to determine the inheritance of resistance to big vein disease, lettuce mosaic virus, and lettuce drop, field resistance to DM, powdery mildew, Fusarium root rot, and Verticillium wilt.