<apex:pageblockSectionItem >
            <apex:outputLabel value="Status"/>
            <apex:outputText value="New"/>
        </apex:pageblockSectionItem>

        <apex:pageblockSectionItem >
            <apex:outputLabel value="Priority"/>
            <apex:selectList size="1" value="{!priority}">
                <apex:selectOptions value="{!priorities}"/>
            </apex:selectList>
        </apex:pageblockSectionItem>
        <apex:pageblockSectionItem >
            <apex:outputLabel value="State"/>
            <apex:selectList size="1" value="{!state1}">
                <apex:selectOptions value="{!states1}"/>
                <apex:actionSupport event="onchange" reRender="a"/>
            </apex:selectList>
        </apex:pageblockSectionItem>
        <apex:outputPanel id="a">
        <apex:pageblockSectionItem >
            <apex:outputLabel value="City"/>
            <apex:selectList size="1" value="{!city1}" id="a1">
                <apex:selectOptions value="{!cities1}"/>
            </apex:selectList>
        </apex:pageblockSectionItem>
            </apex:outputPanel>
        </apex:pageBlockSection>