Develop into a vegetable (6)
I believe the answer is:
sprout
I believe this clue is a double definition.
'develop' is the first definition.
(I know that sprout is a kind of develop)
'a vegetable' is the second definition.
(sprout is a type of vegetable)
'into' is the link.
(Other definitions for sprout that I've seen before include "Burgeon" , "Put out shoots for a brassica" , "Develop new growth" , "Grow like Proust" , "Put forth shoots" .)