Advantage in seed germination (4)
I believe the answer is:
edge
'advantage' is the definition.
(I've seen this before)
'in seed germination' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EDGE' can be found hidden inside 'seed germination'.
(Other definitions for edge that I've seen before include "Bite" , "The part farthest from the middle" , "Border - advantage" , "Rim - move gradually" , "Border or cutting side of knife" .)