Shrub with blight in seed (6)
I believe the answer is:
protea
'shrub' is the definition.
(protea is a kind of shrub)
'blight in seed' is the wordplay.
'blight' becomes 'rot' (both are a type of plant disease).
'in' is an insertion indicator.
'seed' becomes 'pea' (I've seen this before).
'rot' placed into 'pea' is 'PROTEA'.
'with' acts as a link.
(Other definitions for protea that I've seen before include "South African shrub" , "Ascend" , "South African evergreen" , "South African plant" , "S.African flowering shrub" .)