Hi Gopal,
You can try to maintain the setting in SPRO.
"Define Objects in Backend System (Purch. Reqs, Reservations, Purch. Orders)"
under the path
SAP implementation guide->Supplier relationship management->SRM server->Cross Application Basic settings->
Depending upon the configuration, it will either create a PO, PR or reservation based on the product category.
Hope it helps
Regards
Bash