Wildcard support in search in haystack with whoosh

Wildcard support in search in haystack with whoosh

Could anyone help me with implementing the wildcard search in haystack
with whoosh. I have tried to search over google but couldn't found any
concrete example of it. I want to have following behavior over search for
our end user.
When user enters let's 'Crop', the search result should be return all the
records where its one of field is containing this word. The result could
contains all of the following.
Crop and seeds
Crop Types
Types of crops.
I have tried with _startswith, but its only returning records which are
starts with given value. e.g. tag_startswith='xxx'.
Environment Detail:
Django v1.5.3
Haystack v2.1.0
Whoosh v2.5.3

Could someone provide me a concrete example? Any help would be much
appreciated.