Summer fruit (4)
'summer fruit' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for plum that I've seen before include "Prize" , "Very desirable thing" , "Dark bluish-red - fruit" , "Damson-like fruit" , "Dark reddish-purple colour: especially valued" .)
(Other definitions for melon that I've seen before include "Type of fruit" , "Cantaloupe fruit" , "Ogen or cantaloupe, for instance" , "Member of the gourd family" , "Large vine fruit" .)