2005 Annual Report 4d.Progress report. This project serves to document research conducted under a Specific Cooperative Agreement between ARS and Texas A&M University. Additional details of research can be found in the report for the parent CRIS 6202-22000-024-00D Control of Bacterial, Fungal, and Nematode Pathogens of Cotton. This is a new project. The reniform nematode is a major cause of cotton yield losses, and there is no known source of resistance within Upland cotton (Gossypium hirsutum); however, the wild cotton (G. longicalyx) is immune to the reniform nematode. This immunity has been introduced into Upland cotton utilizing a triple species hybrid. However, tracking this immunity is slow and requires the extensive manual labor of growing plants in environmental chambers, adding nematodes to the soil, and counting nematodes in plant roots. If molecular markers could be identified that are tightly linked to the resistance gene, these could be utilized by breeders to select plants that exhibit this trait without extensive laboratory tests. In FY 2005, cytochrome configuration studies were conducted on 10 cells each from 203 plants representing five backcross generations (BC1-BC5). Overall, 66% of the plants in the first three generations were normal, and at least 10% recombination was observed at the BC2 generation. All of the resistant BC4 plants had normal chromosome configuration for Gossypium hirsutum (n=52).