Agricultural epidemics occur when novel strains of fungi appear that are virulent on monocultures of plants. Little is known about how these strains arise or where they come from. Hypotheses of mutation, recombination, or horizontal gene transfer of a virulence factor are proposed to explain the former question. The latter question is usually addressed by invoking host jumps from surrounding plants (e.g. weeds) that may be closely or distantly related, or by long-distance dispersal from distant populations. As a model system, this research focuses on the fungi that occur on wild population of teosinte in Mexico, where this progenitor of maize is endemic, and compare these fungi to those that are found on descendent cultivated populations of maize. Two speices of Fusarium that are significant pathogens of maize have already been found on teosinte. These and other fungi may serve as models for the co-evolution of fungus and host, in terms of pathogenicity and virulence factors, which may include secondary metabolites, and in terms of their population genetics, which may feature broader genetic diversity in the fungi in wild populations cf. agricultural populations and thus exist as reservoirs for novel virulent strains.