ajaxpartialpagerendering for the dropdownlist control created using html tag select

<div>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
      <ContentTemplate>
       <asp:TextBox  ID="tb1" runat="server" ></asp:TextBox>      
        <asp:Label ID="Label1" runat="server"></asp:Label>
        <asp:DropDownList ID="ddl" runat="server" AutoPostBack="true">
              <asp:ListItem>1</asp:ListItem>
              <asp:ListItem>2</asp:ListItem>
        </asp:DropDownList>
        <select id="ddl2" name="ddl2" onchange="submit()" runat="server" />
        
       <asp:Button ID="btnChangeText" runat="server"  OnClick="Button1_Click" Text="submit"/>
        </ContentTemplate>
      </asp:UpdatePanel>
    </div>

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class test10 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            ddl2.Items.Add(new ListItem ("0", "a"));
            ddl2.Items.Add(new ListItem("1", "b"));
          
          
        }
    }
    protected void Button1_Click(Object obj, EventArgs e)
    {
        Label1.Text = tb1.Text;       
       
    }
}