How to add table columns in a dropdownlist (ASP.NET)

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["testConnectionString"].ConnectionString))
            {
                con.Open();
                   //Change with your select statement .
                using (SqlCommand cmd = new SqlCommand("select * from test1", con))
                {
                    DataTable dt = new DataTable();
                    SqlDataAdapter adpt = new SqlDataAdapter(cmd);
                    adpt.Fill(dt);
                    Dictionary<int,> lst = new Dictionary<int,>();
                    foreach (DataRow row in dt.Rows)
                    {
                        //Add values to Dictionary
                        string val = row[1].ToString() + " , " + row[2].ToString() + " , " + row[3].ToString();
                        lst.Add(Convert.ToInt32(row[0]), val);
                    }
                    DropDownList1.DataSource = lst;
                    DropDownList1.DataTextField = "Value";
                    DropDownList1.DataValueField = "Key";
                    DropDownList1.DataBind();
                }
            } 
        }
    }

<asp:DropDownList ID="DropDownList1" runat="server">
</asp:DropDownList>