<select class='slds-select ranklevel' name='Rank Level'  multiple="false" value="{!v.selectedField}">
 <aura:iteration items="{!v.fieldsList}" var="columnsList">
      <option value="{!columnsList.fieldName}" text="{!columnsList.fieldName}"></option>
  </aura:iteration>
</select>

var $j = jQuery.noConflict();
        $j(".ranklevel").chosen({
        width: '95%', create_option: true, persistent_create_option: false, skip_no_results: true});