A petition filed pursuant to section 2-1816 shall be prima facie evidence that (1) it has been properly circulated, (2) the signatures thereon are genuine, (3) the signatures thereon reflect the correct representation of the number of acres specified, (4) the land described therein was devoted to potato production in the last preceding crop year, (5) such petition represents fifty-one percent or more of the commercial acreage in the area designated therein, and (6) each and every other allegation contained therein is true. Any fact contained therein may be rebutted at the hearing before the director.