Maize landraces (Zea mays L.): A new prospective source for secondary metabolite production

Maize (Zea mays L.) is a staple food for millions of people in the world and its grain is converted into well-accepted local food products, including gruels, porridges, pastes and infant weaning food. Maize landraces synthesize a myriad of secondary metabolites and these compounds play important roles throughout the plant's life cycle as mediators in the interaction of the plant with its environment such as plant-insect, pi ant-micro organism and plant-plant interaction. Secondary metabolites determine important aspects in human food quality. Moreover, several plant secondary metabolites are used for the production of medicines, dyes, insecticides, flavors and fragrances. The extensive genetic and chemical diversity of maize results from a long domestication process carried out since Pre-Colombian civilizations. More than 250 maize varieties are known worldwide and their origin is linked directly or indirectly to the maize domestication and breeding processes performed by ancient civilizations. One of the properties of maize is the spectacular diversity in morphology among its races, which is seemingly paralleled by an extensive allelic variation as detected by molecular methods. On the other hand, despite the fact that modern farming techniques have greatly increased the yield of maize, the genetic breeding programs adopted have led to a greater genetic uniformity and a meaningful loss of diversity. In fact, nowadays very few of the world's maize germplasm consist of local and Creole varieties (landraces), showing the genetic vulnerability of that species. In this context, small farmers in some regions of the world still cultivate maize landraces that are populations with high genetic variability and represent a valuable source of potentially useful traits such as resistance or tolerance to biotic and abiotic stress factors. In this review, a few of the major issues that should be taken into consideration in approaching maize landraces as source of secondary metabolites of interest for human health and nutrition will be briefly discussed.