Wheat (Triticum aestivum)

Poaceae family

Wheat is the most important crop worldwide, in terms of acreage and human food. It is an allohexaploid (2n=6x=42, AABBDD genomes), meaning it is descended from three ancestral Near Eastern diploid species. First, T. monococcum (A genome-second from left above) and a T. speltoides relative (B genome-center above) crossed to give rise to AABB tetraploid T. turgidum, emmer wheat (second from right above). Later, emmer and Aegilops tauschii (D genome-right above) crossed to give rise to common wheat.

This genealogy is graphically depicted in the supplemental lecture section of Chapter 4. Winter wheats are commonly grown in the Central and Lower Midwest, where they are sown in the fall, go dormant during the coldest part of winter, resume growth in spring, and mature before the heat of the summer arrives. Spring wheats are commonly grown in the Upper Midwest and the Ukraine, in regions where heat during the summer ripening period is not so severe. Hard wheats, which are the source of high-quality bread flour, are grown in drier areas such as the Great Plains in both spring and winter wheat zones. Soft wheats, the source of all-purpose flour for cookies and cakes, are grown in more humid areas of the eastern and southern U.S.

The hard and soft wheats come in both red and white varieties. Macaroni or durum wheats (T. turgidum var. durum) are grown in the extreme northern U.S.; these tetraploid wheats have harder endosperm and lack the D genome. A closely-related tetraploid, emmer wheat (T. turgidum var. dicoccum), is the primitive ancestor of common hexaploid bread wheat. Wheat belongs to the tribe TRITICEAE.