AJAX :: Update Panel With DropDownList With AutoPostBack="True" Dont Want To Postback It?

IAm using ASP.NET Ajax.
Iam having a Update Panel with DropDownList with AutoPostBack="True"
I dont want to postback it, but it going postback, i dont want AutoPostBack="false"
.

Here my code:
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering ="true" >
</asp:ScriptManager>
<br />
<br />
<div>
</div>
<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack ="true" OnSelectedIndexChanged ="DropDownList1_SelectedIndexChanged" >
<asp:ListItem Value="0">----Select----</asp:ListItem>
<asp:ListItem Value="101">General Admin</asp:ListItem>
<asp:ListItem Value="102">Admin Assistant</asp:ListItem>
<asp:ListItem Value="103">Software</asp:ListItem>
<asp:ListItem Value="104">Recruiting</asp:ListItem>
</asp:DropDownList>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode ="Conditional" >
<ContentTemplate >
<asp:DropDownList
ID="DropDownList2" runat="server">
<asp:ListItem Value="0">----Select----</asp:ListItem>
<asp:ListItem></asp:ListItem>
</asp:DropDownList>
</ContentTemplate>
<Triggers >
<asp:AsyncPostBackTrigger ControlID ="DropDownList1" EventName ="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
</form>