The Effect of
Solar Irradiance on the Mortality of Phakopsora pachyrhizi
Urediniospores |
|
| The objective of this study was to determine the relationship between soybean rust urediniospore viability and exposure to solar radiation. Our aim is to improve the accuracy of aerobiology-based modeling systems (e.g., USDA Soybean Rust Information System) and facilitate predictions of P. pachyrhizi dispersal to soybean fields in the middle latitudes of North America from overwintering habitats in the subtropics. The field portion of the research was conducted by Nick Dufault (CEAL Ph.D. student) and Scott Isard (CEAL) during February and March 2005 on the Centro Regional de Investigatión Agrícola station in Capitán Miranda, Paraguay. Drs. Monte Miles and Glen Hartman from the ARS National Soybean Research Laboratory provided advice in the field and Erick DeWolf and Joe Russo helped with planning the study and analyzing our field data. |  Irradiance measurements |
 Spore exposure |
Nick and Scott exposed urediniospores of P. pachyrhizi in a courtyard to determine the deleterious effects of sunlight. Concomitant total solar (0.285-2.8 µm) and ultraviolet (0.295-0.385 µm) irradiance measurements were used to predict urediniospore germination. They found that urediniospores exposed to doses of solar and ultraviolet (UV) radiation = 28 MJ m-² and =1 MJ m-², respectively, did not germinate. The proportions of the urediniospores that germinated, normalized with respect to the germination proportion for unexposed urediniospores from the same collections, were a linear function of solar irradiance (R² = 0.83). UV measurements predicted normalized germination proportions equally well. Results of inoculation experiments that we conducted in the stations greenhouse with exposed P. pachyrhizi urediniospores supported the results of the germination trials. The relationship between urediniospore viability and exposure to solar radiation has been incorporated into the soybean rust aerobiological model that provides North American soybean growers with decision support for managing soybean rust. |
| Isard, S. A., Dufault, N. S., Miles, M.
R., Hartman, G. L., Russo, J. M., De Wolf, E. D., and Morel, W. 2006. The effect of solar irradiance on the mortality of Phakopsora pachyrhizi urediniospores. Plant Dis. 90:941-945. |
|