King Edward, say, initially took over in Germany (5)
I believe the answer is:
tuber
'king edward' is the definition.
(King Edward is a type of potato)
'initially took over in germany' is the wordplay.
'initially' suggests taking the first letters.
'over in germany' becomes 'uber' (German for 'over').
The first letter of 'took' is 't'.
't'+'uber'='TUBER'
'say' is the link.
(Other definitions for tuber that I've seen before include "Thickened underground stem" , "Thickened fleshy root" , "traveller down in London?" , "Fleshy underground stem (eg of the potato)" , "Rhizome, as of potato" .)