Fruit star trained with food writer Mary (10)
I believe the answer is:
strawberry
'fruit' is the definition.
(I know that strawberry is a aggregate fruit)
'star trained with food writer mary' is the wordplay.
'trained' is an anagram indicator (to train can mean to grow something into a shape).
'with' becomes 'w' (abbreviation).
'food writer mary' becomes 'Berry' (Mary Berry, food writer, chef and TV presenter).
'star' is an anagram of 'stra'.
'stra'+'w'+'berry'='STRAWBERRY'
(Other definitions for strawberry that I've seen before include "Soft red fruit" , "Sort of blonde" , "Eleven [NAEVUS]" , "Summer fruit" , "Hill building Gothic" .)