A fiduciary acting as the guardian of a minor, or as the guardian or committee of an insane person must file a return for such minor or person, unless the minor himself makes a return or causes such return to be made. A return must be filed for a minor or insane person who is single where adjusted gross income of such person exceeds the limits set forth in Section 18505 of the Revenue and Taxation Code. Returns must be filed for such married couples where their adjusted gross income exceeds the limits set forth in Section 18505 of the Revenue and Taxation Code. Regardless of net income, a return must be filed for all persons, whether married or single, if their gross income exceeds the limits set forth in Section 18505 of the Revenue and Taxation Code. The return which must be filed for the persons described above is Form 540 if such persons are residents, and Form 540NR if such persons are nonresidents.

For the purpose of determining the liability of a fiduciary to render a return under the provisions of the preceding paragraph in cases where the minor or the incompetent is married, it is the aggregate gross income or the aggregate net income of both husband and wife which is controlling. (See Section 18501 of the Revenue and Taxation Code)