It does not appear to be currently supported. Here is the relevant source:
http://trac.edgewall.org/browser/trunk/trac/ticket/templates/query_results.html?marks=77-86,91,101#L65So you'd have to submit an enhancement request. Here is a patch against r11100 of the Trac trunk which I think does the job. It has been very lightly tested ;)
Index: trac-trunk/trac/ticket/templates/query_results.html
===================================================================
--- trac-trunk/trac/ticket/templates/query_results.html (revision 11100)
+++ trac-trunk/trac/ticket/templates/query_results.html (working copy)
@@ -80,6 +80,7 @@
<py:when test="name == 'reporter'">${authorinfo(value)}</py:when>
<py:when test="name == 'cc'">${format_emails(ticket_context, value)}</py:when>
<py:when test="name == 'owner' and value">${authorinfo(value)}</py:when>
+ <py:when test="name == 'description'">${wiki_to_html(ticket_context, value)}</py:when>
<py:when test="name == 'milestone'"><a py:if="value" title="View milestone" href="${href.milestone(value)}">${value}</a></py:when>
<py:when test="header.wikify">${wiki_to_oneliner(ticket_context, value)}</py:when>
<py:otherwise>$value</py:otherwise>