concatenar datos de una tabla en un combobox en visual c#

[beyaco21cl]

Les coloco mi codigo

private void cbb_Cadena_SelectedIndexChanged(object sender, EventArgs e)
{
if (flag == 0){ }
else
{
open_DB();

using (SqlCommand cmd2 = new SqlCommand())
{
DataSet DsComercio = new DataSet();
cmd2.CommandText = @"select CodComercio, NombComercio from sip.dbo.comercio where codcadena=" + cbb_Cadena.SelectedValue;
cmd2.CommandTimeout = 16000;
cmd2.Connection = connDB;
SqlDataAdapter DaRec2 = new SqlDataAdapter(cmd2);
DaRec2.TableMappings.Add("Table", "Customers2");
DaRec2.Fill(DsComercio);

cbb_Comercio.DataSource = DsComercio;
cbb_Comercio.DataSource = DsComercio.Tables[ 0].DefaultView;
}
cbb_Comercio.DisplayMember = "NombComercio";
cbb_Comercio.ValueMember = "CodComercio";
flag = 1;
cbb_Comercio.Enabled = true;
flag1 = 1;
}
}