MySqlCommand _comandoDados = new MySqlCommand(String.Format(
              "select EMGroot.id, EMGroot.lbs_net, EMGroot.lbs_gross_aai, EMGroot.price_brazil, sum(AAIest.qtd_venda) " +
              "from eaglemo4_eaglemotorsg.tb_products_root EMGroot " +
              "inner join eaglemo4_americai.tb_estoque AAIest " +
              "on AAIest.id_produto = EMGroot.id " +
              "where EMGroot.manupart = '" + txtManuPartInserir.Text + "'"), conexao_aai);

        MySqlDataReader Open_readerteste = _comandoDados.ExecuteReader();
        Open_readerteste.Read();

if(Open_readerteste.HasRows)
   {
     root_id = Open_readerteste.GetInt16(0)
     ....
   }