Take a look at this line:
string query = "select distinct convert(varchar,Item_GenName) from ItemMasterlistTable where datalength(Item_GenName) != 0";
This returns something like:
(No column name)
. So, change it as follow:
string query = "select distinct convert(varchar,Item_GenName) AS Item_GenName from ItemMasterlistTable where datalength(Item_GenName) != 0";
then you'll be able to refer to column
Item_GenName