Monsanto has acquired WestBred LLC, a company specializing in wheat germplasm. Currently, the big seed companies specialize almost entirely in corn and soybeans, largely thanks to demand driven by subsidies. Wheat, one of the world's most important crops, was historically maintained and improved almost exclusively by public sector plant breeders.
Wheat was originally neglected by the private seed industry due to its lack of heterosis. Heterosis, or hybrid vigor, is the poorly understood process whereby the hybrid offspring off two different varieties of a crop is stronger and more high-yielding than its parents. This effect does not extend to the 3rd generation. This effect is so strong that farmers several decades ago began purchasing hybrid seed instead of saving their own as the increased yield was worth more money than the cost of seed plus any risk of dependence on the seed salesman. This didn't happen with wheat though. Without hybrid vigor, no company could quickly produce a new product valuable enough for a farmer to buy. Besides, prior to current patent laws, there was nothing to stop a farmer from buying expensively-bred seed and illegally propagating it himself.
Maize DOES benefit from heterosis, and it was the new business of selling hybrid maize seed that launched the private seed industry and the private plant breeder. The private seed industry made incredible progress improving maize varieties and farmers have eagerly bought the newest, hottest seeds each year ever since.