Tube where growths come up (5)
I believe the answer is:
straw
'tube' is the definition.
(thesaurus)
'growths come up' is the wordplay.
'growths' becomes 'warts'.
'come up' shows that the letters should be reversed in order.
'warts' in reverse letter order is 'STRAW'.
'where' acts as a link.
(Other definitions for straw that I've seen before include "Pale yellow colour" , "Bedding material for horses etc" , "Remains of corn" , "What a sucker gets given" , "politician" .)