I have bee trying to render a field based on lead status value like 'Cancel/Rejected'. if i select Cancel  value it should display field A, if i select value Reject it should display field B. please take a look at my visualforce page. What am i missing ?

vfpage

                    <apex:actionRegion >
                        <apex:selectList id="chooseColor" value="{!str}" size="1">
                            <apex:selectOption itemValue="Approved" itemLabel="Approved"/>
                            <apex:selectOption itemValue="Rejected" itemLabel="Rejected"/>
                            <apex:selectOption itemValue="Cancel" itemLabel="Cancel"/>
                            <apex:actionSupport event="onchange" reRender="col"/>
                        </apex:selectList> 
                    </apex:actionRegion> 
                    </apex:column>
                    <apex:column id="col" headerValue="Cancel Reason" > 
                        <apex:inputField value="{!le.Lead_Cancel}" />  
                     </apex:column>
                     <apex:column id="col2" headerValue="Reject Reason" > 
                         <apex:inputField value="{!le.Rejected_Details__c}" />  
                     </apex:column>