Vegetable as incentive (6)
I believe the answer is:
carrot
This clue is a double definition.
'vegetable' is the first definition.
(carrot is a kind of vegetable)
'incentive' is the second definition.
(as in a carrot and stick)
'as' is the link.
(Other definitions for carrot that I've seen before include "Orangey vegetable" , "Incentive (but not the stick)" , "Obstacle in race" , "Vegetable - incentive" , "Pointed vegetable" .)