Dispersal and mating pattern of two plant pathogens. In part as: Spatial and temporal dynamics of Puccinia andropogonis on Comandra umbellata and Andropogon gerardii in a native prairie and inbreeding levels of two Ustilago maydis populations

Plant pathogenic fungi cause billions of dollars of damage to agricultural crops annually. Understanding pathogen genetic variability and dispersal are two important questions that need to be addressed in controlling plant disease. This research looked at both questions, but in two different organisms. The first project utilized a naturally-occurring disease of a native prairie grass to look at basic questions of pathogen dispersal. The second project used a well-characterized disease of corn to investigate genetic variability.; Most of our knowledge about dispersal of plant pathogenic rust fungi comes from their study in agricultural systems. To better understand the pathogen, this study utilized a naturally-occurring rust fungus that infects two common prairie plants, Andropogon gerardii (big bluestem) and Comandra umbellata (comandra). Mean rust severity on big bluestem was regressed on the number of aecia on comandra within eight distance intervals (aecial density) from big bluestem plants, where greater distances included aecia at shorter distances. There was a significant positive relationship between aecial density on comandra and rust severity on big bluestem that decreased with increasing distance in accordance with the power law model, becoming non-significant at distances >40m.; Smut fungi, like other basidiomycetes, are capable of both outcrossing and inbreeding through mating of compatible haploid progeny. Determining the level of inbreeding in Ustilago maydis, a smut fungus infecting maize, may be helpful in evaluating pathogen dispersal and the maintenance of genetic variability in this smut fungus. To estimate the level of inbreeding in U. maydis, two cornfields were sampled, one in North America (Le Sueur, Minnesota) and one in South America (Tarariras, Uruguay). The fields were selected because of their geographic isolation and host management differences. The results of this study demonstrate that smut infections in both cornfields were predominately from outcrossing U. maydis populations, suggesting that teliospores are infrequently dispersed and isolated as single infection units. Genetic diversity within and between the two cornfields was high, with total genetic diversity mostly attributable to diversity within populations.