Overwintering survival of stem rust on perennial ryegrass : construction of a simulation model, and effects of the mycoparasite Sphaerellopisis filum Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6w924g00s

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  • Stem rust, caused by the fungus Puccinia graminis subsp. graminicola, can cause yield reductions exceeding 90% on perennial ryegrass (Lolium perenne L.) crops grown for seed if not treated with fungicide in the spring. There is evidence that late-spring stem rust epidemics are initiated by populations that survived the winter. In addition, a previously developed stem rust severity model indicates that the late-spring epidemic severity is proportional to the stem rust population that overwintered. In this study, a mathematical model was constructed to describe the biological processes of stem rust overwintering as a function of meteorological conditions. The model was validated with two years of stem rust severity data collected at two field sites. After model validation, the effects of changing the sporulation or daily infection conditions on overwintering stem rust foci were quantified. The model indicated that reducing the infection conditions or sporulation rate over the winter would reduce the stem rust population in the spring. A mycoparasite of stem rust, Sphaerellopsis filum (Biv.-Bern ex Fr.) Sutton (teleomorph Eudarluca caricis (Fr.) Eriksson), is known to infect the uredinia of other rust species and to lower spore production capacity. The effects of S. filum on individual stem rust uredinia and on overwintering populations were quantified. S. filum and stem rust were inoculated under controlled conditions in the glasshouse. In the field, S. filum was applied to plots that were naturally infected with stem rust at two sites in two years. S. filum infected stem rust uredinia in the glasshouse and field under conditions typical of an Oregon winter, and reduced spore production capacity. Furthermore, winter applications of S. filum or one winter application of a fungicide reduced the stem rust overwintering population at several field sites on first-year stands of perennial ryegrass. Treatment effects were not observed on second-year stands of perennial ryegrass, which had lower levels of disease severity than first-year stands during both years. These studies suggest several IPM strategies that could be utilized to reduce the severity of stem rust epidemics on perennial ryegrass. These strategies might include lowering the spore production capacity of stem rust by introducing effective strains of S. filum, or applying a fungicide to first-year stands over the winter.
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