Culture expert to call back conclusively, nurseryman claims (10)
I believe the answer is:
folklorist
'culture expert' is the definition.
'to call back conclusively nurseryman claims' is the wordplay.
'conclusively' indicates one should take the final letters (the letter which concludes the word).
'nurseryman' becomes 'florist' (flowers may be grown in a nursery).
'claims' indicates putting letters inside.
The last letters of 'to call back' are 'olk'.
'olk' put into 'florist' is 'FOLKLORIST'.
(Another definition for folklorist that I've seen is " One versed in traditional customs".)