Tropical maize: Exploiting maize genetic diversity to develop a novel annual crop for lignocellulosic biomass and sugar production

Maize (Zea mays L.) is truly a remarkable crop species, having been adapted from its tropical origins to a wide diversity of environments and end uses. According to the Food and Agriculture Organization of the United Nations FAOSTAT webpage, 792 million metric tons of maize were produced worldwide in 2007, making it the world's highest yielding grain crop (http://faostat.fao.org/site/ 339/default.aspx). When maize varieties adapted to tropical latitudes are grown in temperate environments such as the US Corn Belt, they flower later and produce little or no grain, but have higher total biomass yields compared to modern commercial corn grain hybrids (Fig. 1). Further, tropical maize also accumulates high amounts of extractable stalk sugar (sucrose, glucose, and fructose) because of reduced grain formation. Although offering potential benefits as a feedstock for biofuels, the direct use of tropical maize germplasm in temperate environments is hampered by greater lodging, less stress tolerance, and susceptibility to disease and insect pests - traits that have been greatly improved in modern US corn grain hybrids. However, hybrids derived from crossing temperate-adapted and tropical parents successfully combine the high biomass potential of tropical maize with the genetic improvements from the past century of corn breeding for high grain yields in temperate environments. Named tropical maize, these tropical x temperate hybrids produce greater biomass and sugar compared to current US corn hybrids using at least 50% less nitrogen (N) fertilizer inputs (Table 1)