Sub-Saharan staple (3)
I believe the answer is:
yam
'sub-saharan staple' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for yam that I've seen before include "vegetable plant" , "Tropical tuber" , "Edible tuber" , "May be a sweet potato" , "Tropical climber" .)