This hexaploid called T. aestivum . Has a hard endosperm and best for bread making. Hexaploid wheat is not known to occur in the wild. Winter and spring wheat. Most of our good wheat cultivars are derived from wheat brought to the U.S. by Mennonites in late 1800's from the Russia and the Ukraine.
Wheat has lots of disease problems.
Puccinia graminis , or wheat rust, is one of the worst of these. Production of cultivars with resistance is very important. They tend to last about three years before disease catches up. Difficult to make hybrids. Wheat grown in cool, dry climates most.