Food mum fed to Dorothy's dog (6)
I believe the answer is:
tomato
'food' is the definition.
(tomato is a kind of food)
'mum fed to dorothy's dog' is the wordplay.
'mum' becomes 'ma' (ma can mean mother).
'fed to' means one lot of letters goes inside another.
'dorothy's dog' becomes 'toto' (Dorothy's dog in The Wizard of Oz).
'ma' placed into 'toto' is 'TOMATO'.
(Other definitions for tomato that I've seen before include "It's also known as a love apple" , "Part of a BLT sandwich" , "that's suitable to eat" , "Shiny red fruit" , "A glossy red fruit eaten as a vegetable" .)