It is possible to set dependencies between two tickets: either depends on or blocked.
In theory blocked might be a typo because JSONs imported with pgimport has attributes blocks and depends. And I tried that attribute depends is mapped to the field depends on.

I will describe steps which I done in staging instance https://stg.pagure.io/dependencies-test/i
1. Create a tracker ticket 1 which must be closed as last one. Title "Tracker bug" https://stg.pagure.io/dependencies-test/issue/1
2. Create 2nd ticket which should be implemented before ticket1. " Implement sub-feature1" Title https://stg.pagure.io/dependencies-test/issue/2
3. Jump back to ticket1 and set depends on. I added "#2" to the field.
4. Jumb back to ticket 2 and try to close it.

Expected result:
Ticket will be closed without any problem; because ticket1 depends on ticket2 and ticket 2 does not depend on anything.

Actual result:
Ticket cannot be closed and error is printed in the top of page:
**You cannot close a ticket that has ticket depending that are still open. **