Analytical testing and laboratory determination for analyte or quality constituent shall be based upon the appropriate standards promulgated by the U.S. Department of Agriculture, applicable standards prescribed by the laws of the State where the particular product was produced, specifications of any governmental agency, written buyer and seller contract specifications, or any written specifications by an applicant which is approved by the Administrator; Provided, That, if such product is regulated pursuant to the Agricultural Marketing Agreement Act of 1937, as amended (7 U.S.C. 601 et seq.), or the comparable laws of any State, such testing and determination shall be on the basis of the standards, if any, prescribed in, or pursuant to, the marketing order and/or agreement effective thereunder.