Upon receipt of the petition, the board of supervisors shall immediately refer the petition to the agricultural commissioner who shall examine it by reference to the register of cottongrowers, and shall, within 15 days after receiving the petition, return the petition to the board of supervisors with his or her certificate attached thereto certifying from the cottongrowers register that the petition qualifies as valid. The certificate of the agricultural commissioner shall be conclusive as to the sufficiency of the signatures on the petition.