Bread variety (3)
(Other definitions for oat that I've seen before include "Cereal (singular)" , "Cereal grass" , "Cereal plant" , "Food grain" , "Basis of porridge" .)
'bread variety' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rye that I've seen before include "East Sussex resort" , "Cereal - liquor" , "Grain used in flour and whiskey" , "Gypsy gentleman" , "J D Salinger novel 'The Catcher in the ...'" .)