Tropical Environments, Biodiversity, and the Origin of Crops

Plants play an important, but often insufficiently recognized. role in human societies, chiefly as providers of food, feed, and fiber, but for other uses as well such as drugs and building materials. In those cases where demand for a particular plant product exceed natural supply, humans initiated cultivation of those plants 10,000 years ago, resulting in the domestication of a limited number of species in several areas of the world, generally located in tropical and subtropical areas. Tropical and subtropical areas consist of several ecozones defined by climate, soil, and vegetation and fauna. One of the major factors distinguishing tropical ecozones is the distribution of rainfall and particularly the length of the dry season, if any. From a biological standpoint, most of biodiversity is concentrated in tropical areas. This may explain in part why the majority of crops discussed in this volume originated in either tropical or subtropical ecozones with summer rains or in the tropical ecozone with year-round rains. The fundamental contribution of genomics to plant breeding is to provide information on the genotypic basis of phenotypic variation. Based on this information, marker-assisted selection systems can be developed that can increase the efficiency at identifying agronomically useful diversity and transferring it into improved cultivars. In turn, marker-assisted selection is expected to increase the efficiency of plant breeding. To achieve this goal, however, genomic resources have to be developed, not only in model species, but especially in target species as illustrated in this volume. Having access to a diverse set of improved crops is a critical element of strategies to alleviate food insecurity and poverty, which affect disproportionately rural populations. Recently, the goal of increasing crop productivity has taken added urgency because of the combined impact of the focus on biofuels and global warming. Genomics is a crucial tool in raising crop productivity for the foreseeable future.