Ann Romney, the wife of Republican presidential nominee Mitt Romney, is to substitute for ailing Robin Roberts as co-anchor on \"Good Morning America.\" The Hollywood Reporter said Romney is to appear on Wednesday\'s edition of the morning program alongside Roberts\' co-anchor, George Stephanopoulos, and correspondents Lara Spencer, Josh Elliott and Sam Champion. ABC News is in discussions with first lady Michelle Obama to pull a shift as co-host of \"GMA,\" the entertainment industry trade newspaper said. Stephen Colbert, Oprah Winfrey, Diane Sawyer, Katie Couric, Barbara Walters and Jessica Simpson have all signed up to help with the broadcast in Roberts\' absence. Roberts, a breast-cancer survivor, left the show temporarily during the summer to undergo a bone-marrow transplant to battle myelodysplastic syndrome, a rare blood disease that can be caused by chemotherapy.