Spray a 9x9x2-inch baking pan with nonstick spray; set pan aside.
In a large mixing bowl combine the 2 cups flour, granulated sugar, 1/4 cup brown sugar, wheat germ, baking powder, orange peel, cinnamon, baking soda, and nutmeg. In another bowl combine the milk, egg, egg whites, yogurt, and oil. Beat until smooth. Add liquid ingredients to flour mixture, stirring just until combined. Combine 1-1/2 cups blueberries and 1 tablespoon flour; stir into batter. Pour batter into prepared pan.
For the Crumb Topping, in a small bowl combine walnuts, 1/4 cup all-purpose flour, 1/4 cup packed brown sugar, and melted margarine. Mix until crumbly. Sprinkle over batter.
Bake in a 375 degree F oven for 35 to 40 minutes or until a toothpick inserted near the center comes out clean. Serve warm or cool in pan on a wire rack. Garnish with additional fresh blueberries and mint, if desired. Makes 9 servings.