Bring 4 quarts water to a boil in a large Dutch oven. Add rutabaga; return to a boil, and cook for 3 minutes. Add potatoes; return to a boil, and cook 1 minute. Drain well, and return to pan; set aside.
Place flour, salt, and pepper in a medium saucepan. Gradually add skim milk, stirring with a wire whisk until blended. Bring to a boil over medium-high heat, and cook 1 minute or until thickened, stirring constantly. Remove from heat, and add the cream cheese and Worcestershire sauce, stirring constantly until cream cheese melts. Pour over rutabaga and potatoes; toss gently to coat.
Spoon mixture into an 11 x 7-inch baking dish coated with cooking spray. Cover and bake at 350° for 45 minutes. Sprinkle breadcrumbs and parsley over casserole, and bake, uncovered, an additional 15 minutes.