Edible bulb used in canneloni only (5)
I believe the answer is:
onion
'edible bulb' is the definition.
(I've seen this before)
'in canneloni only' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ONION' is hidden within 'canneloni only'.
'used' is the link.
(Other definitions for onion that I've seen before include "Bulb used as a vegetable" , "Plant with edible bulb" , "The tear-inducing vegetable" , "associated with 26 [TRIPE] ?" , "Bulbous vegetable" .)