First man made cereal is

The first man-made cereal is Triticale.
Triticale is a hybrid of wheat (Triticum) and rye (Secale) first bred in laboratories during the late 19^th century in Scotland and Germany.
Triticale is almost always a second-generation hybrid, i.e., a cross between two kinds of primary (first-cross) triticales. When crossing wheat and rye, wheat is used as the female parent and rye as the male parent (pollen donor).