Develop into vegetable (6)
I believe the answer is:
sprout
This clue is a double definition.
'develop' is the first definition.
(sprouting is a kind of developing)
'vegetable' is the second definition.
(sprout is a kind of vegetable)
'into' acts as a link.
(Other definitions for sprout that I've seen before include "Push out new shoots" , "Small cabbage from Brussels?" , "Bud; a type of cabbage" , "Start to grow" , "Germinate" .)