Dissertation Research: The Role of Pathogens in the Maintenance of Host Genetic Variation

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Agricultural crops, which are usually planted as genetic monocultures, are notoriously prone to disease. Natural plant populations, by contrast, are rarely as infected by disease; they are also typically genetically variable. Recently, biologists have postulated that the genetic diversity typical of natural populations may be a product of natural selection exerted by disease organisms, but few studies have tested this hypothesis. The investigators will examine the role of disease in maintaining host genetic variation by comparing resistance of closely related species in the mustard family to a rust disease. Some of these mustard species have no genetic variability, whereas other species are genetically variable. For disease to be capable of promoting genetic variation, the disease must exert strong selection on its hosts; that is, it must decrease survival and/or reproduction of the hosts, and resistance must be inherited. The goals of this study are to determine whether these conditions are met, as well as to determine whether the genetically uniform species are less resistant to disease than the genetically variable species, and whether the composition of natural vegetation is different in places with and without this disease.