Textures cannot be assigned to individual symbols directly through the Object Info palette. Textures must be applied to the separate components of the symbol. This can be done using the Edit Symbol command as described here, or by Applying Object and Component Textures by Class. Complex objects can contain more than one class. Texture changes affect all instances of that symbol.
To apply a texture to the symbol components:
Select the symbol to edit.
Select Modify > Edit Symbol.
The Edit Symbol window opens; see Editing Symbol Definitions for more information on the Edit Symbol window.
Select the first component that requires a texture.
On the Attributes palette, select any Fill Style other than None (otherwise the texture will not render).
Click the Render tab from the Object Info palette.
Select the desired Texture from a library or the current file, and then edit the mapping parameters as described in Applying and Mapping Textures.
Repeat steps 3–6 for each component of the symbol.
Select Modify > Exit Symbol once all changes have been applied.