Browsing by Subject "Puccinia coronata"

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    Genetic and ecological constraints to the evolution of virulence and reproduction in a plant pathogen
    (2012-12) Bruns, Emily Louise
    Hosts and pathogens are engaged in an ongoing evolutionary struggle. In humanmanaged systems, rapid evolution of pathogen populations can reduce the effectiveness of important control methods such as antibiotics and genetic resistance in crop species. My thesis research investigates potential constraints to pathogen evolution by examining genetic and ecological factors affecting the evolution of infection and reproduction in the plant pathogen Puccinia coronata. I first investigate genetic variation underlying three pathogen life history stages within the host and show that variation in pathogen life-history stages within the host is affected by both the pathogen and host genotype. Next, I evaluate the relationship between pathogen infection and reproduction and show evidence of a trade-off between the number of resistant host genotypes infected and two key pathogen life history traits. Finally, I quantify the variation in infection and reproduction among eight different agricultural populations of P. coronata and ask whether the genetic diversity of the host population affects the evolution of pathogen infection and reproduction. While I do not find conclusive evidence that host genetic diversity affects the evolution of these traits, I do I find significant variation among populations that is not explained by pathogen population structure, indicating that selection structures pathogen populations.
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    A "Pan American" approach to durable crown rust resistance in oats : evaluation of a seedling resistance covariance method.
    (2010-04) Junior, Adolar Freitag
    Crown rust, caused by Puccinia coronata, is the most important disease of oats worldwide. Methods of control have usually been based on single major genes that confer complete resistance, but with the emergence of new races this resistance is easily overcome. Thus, partial resistance is believed to be more effective in controlling the disease because it promotes coexistence of host and pathogen and thus slows the evolution of pathogen virulence. Therefore, creating durable resistant lines depends on several aspects and choosing parental lines is one of the most important. However, methods to predict the best parental combinations and their progeny performance are not reliable. Since the University of Minnesota oat breeding program began in 1889, many cultivars have been released. On average 150 new lines are selected every year for multiple location yield trials. With the number of lines available and the necessity for reducing the number of crosses to save labor, time, money and space, we attempted to identify a method to predict the superior test cross combinations involving parental lines with genetic diversity between resistance genes. We used a covariance analysis based on the results from the seedling rust tests of parental lines, where the original data based on rust reaction types (HR – highly resistant; R – resistant; MR – moderately resistant; MS – moderately susceptible and S – susceptible) were transformed to numbers (5, 3, 1, -1 and -3), respectively. Every possible pairing combination was done with all parental candidates. A large negative covariance indicated that the parents had substantial genetic diversity between them, which was preferred because then a resistant gene in one parent could match the deficiency in another parent. Eleven populations from different crosses iii were evaluated for crown rust resistance. The covariance between parents for these crosses varied from -0.5864 to +0.5304, which indicated more and less genetic diversity among parents. The most similar parental pair was used as a control to test our hypothesis. In our study covariance analysis was not able to predict the best parental combination for maximum potential crown rust resistance in progenies, but crossing parental lines with higher resistance levels produced lines with consistently lower disease infection and a higher proportion of resistant individuals.