Warts develop on tube (5)
I believe the answer is:
straw
'tube' is the definition.
(I know that straw is a type of tube)
'warts develop' is the wordplay.
'develop' is an anagram indicator.
'warts' with letters rearranged gives 'STRAW'.
'on' is the link.
(Other definitions for straw that I've seen before include "remnant of harvest" , "Cornstalks (often the last)" , "Dried stalks for fodder" , "Thin tube; yellow" , "Plant fibre used as fodder" .)