2006 Annual Report 4d.Progress report. This report documents research conducted under trust fund agreement between the ARS and the Arizona Iceberg Lettuce Research Council. Additional details can be found in the report for the parent project 5305-21000-011-00D; Evaluation, Enhancement, Genetics & Breeding of Lettuce, Spinach, Melon & Closely Related Species. Our objectives are to incorporate disease resistance into crisphead lettuce cultivars and breeding lines adapted to low desert production conditions. Major breeding efforts targeted resistance to lettuce big vein, Fusarium root rot, lettuce drop (Sclerotinia sclerotiorum), tipburn, and powdery mildew. In 2005, we confirmed resistance of previously identified germplasm to big vein, lettuce drop, and powdery mildew; we obtained preliminary data on inheritance of resistance to Fusarium root rot. Advanced breeding lines were evaluated and selections were made for resistance to bolting, tipburn, big vein, powdery mildew, and lettuce drop.