Possible Clues:

• Dangling incentive
• Orange treat for horses
• Vegetable grown underground
• Orangey vegetable
• Would the car go to ruin if this was the root of the trouble?
• Vegetable - incentive
• You'd be an ass to accept such a bribe to make the motor decay
• Subject of a myth about night vision
• The vegetable to induce
• Enticement; vegetable