For the initial board any wheat producer may be elected only if he first has his name placed on the ballot by filing with the Director a petition containing a number of signatures equal to the lesser of 50 or 5% of those producers in his district qualified to vote on the referendum. All candidates shall be natural persons who are producers and residents in the district for which they are nominated. Notice of the initial election of members of the board shall be given in trade publications, the public press, and statewide newspapers at least 2 weeks prior to the election. Vacancies on the wheat development board during the term of office shall be filled by the wheat development board with a producer from the district for the balance of the unexpired term. In subsequent years, an election shall be held to fill any expiring term on the board. Elections shall be in the same fashion as for initial board members. The election procedure shall be as provided in this Section unless otherwise provided for in the wheat development program. Candidates receiving the greatest number of votes at any election shall be elected.