Fossil docs says that markdown can be used in tickets as well. But I do not manage to turn it on.
https://www.fossil-scm.org/xfer/tktview/35343257ffd02ba47880 reports a similar problem.
I read a solution in the Fossil-scm mail list but I cannot find the exact email now. However I put my TH1 templates for ticket in the following snippet:
https://bitbucket.org/snippets/ivzhh/GeL9pq
The basic idea is to set $mutype to markdown (x-markdown or x-fossil-markdown). Then add the redering code on line 75~82 in ticket-edit.tcl (the original solution is this post). The markdown rendering returns two values instead of one (default fossil wiki command). Please check the snippet.