Warts develop on the tube (5)
I believe the answer is:
straw
'the tube' is the definition.
(thesaurus)
'warts develop' is the wordplay.
'develop' indicates an anagram.
'warts' is an anagram of 'STRAW'.
'on' acts as a link.
(Other definitions for straw that I've seen before include "Stalk - tube for drinking" , "Remains of corn" , "Residue of cereal crop" , "Warts (anag.)" , "remnant of harvest" .)