APS Abstracts of Presentations

The effects of solar radiation on the mortality of Phakopsora pachyrhizi urediniospores
N. S. DUFAULT (2), S. A. Isard (2), M. R. Miles (3), G. L. Hartman (3), E. D. De Wolf (2), W. Morel (1)
(1) Centro Regional de Investigation Agricola, Capitan Miranda, Itapua, Paraguay; (2) Pennsylvania State University, University Park, PA, USA; (3) University of Illinois, Urbana, IL, USA
Phytopathology 96:S31

Solar radiation, especially ultraviolet radiation, is an important factor associated with the mortality of fungal spores during long distance transport. A more complete understanding about the effect of solar radiation on the viability of Phakopsora pachyrhizi urediniospores may increase the accuracy of current transport models in the U.S. To examine the relationship of solar radiation on urediniospore viability, spores were exposed to solar radiation for varying lengths of time in a natural environment. Exposed spores were incubated on water agar for 18 h in darkness at 20°C, and the proportions of germinating spores were normalized to the germination of un-exposed spores. A linear relationship (R(^2) = 0.83) was observed between solar irradiance and the normalized proportion of germinating spores. Spores did not germinate after being exposed to doses of less than or equal to 28MJ m(^–2). Spore viability was confirmed with a bioassay that included inoculating soybean plants with both exposed and unexposed urediniospores. The proportion of pustules observed per trifoliate, relative to unexposed spores, was 0.82 and 0.29 for the solar irradiance doses of 10 and 23 MJ m(^–2) respectively. These values were similar to the germination proportions estimated by the model at the same exposure levels.

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