Organizing Committee


Poster Presentations


Poster Presentations


Analysis of cloud effects on the development of Asian soybean rust in Brazil and South Africa

Presenter: A. P. S. Dias

All authors and affiliations: A. P. S. DIAS, X. B. Yang, and X. Li. Iowa State University, Department of Plant Pathology, Ames, IA

Our other studies suggest that Asian soybean rust (ASR) is sensitive to light. Disease was more severe with a period of shading compared to no shading. ASR outbreaks in Brazil were correlated to the number of rain days, particularly in regions where continuous cloudiness follows rainfall. The disease was overestimated by rainfall-based models in regions where short-duration storms are common. Those evidences suggest that adding shade effects from clouds may improve the prediction of ASR epidemics. This study was to determine the cloud effects on ASR outbreaks by simulating disease development in Brazil and South Africa. Daily disease increments were calculated, assuming fixed initial inoculum and variable rates as a function of cloudiness. In sunny days, the disease rates are reduced to 5% of those in cloudy days (days with >8 h of overcast sky). Final disease estimates were compared to field observations. The simulations were consistent with field reports (Pearson’s correlation -r > 0.9). The unusual epidemic years in Bahia, Brazil, and North KwaZulu Natal, South Africa, were successfully predicted by the cloudiness-based model. In general, severe ASR outbreaks occurred when >15 cloudy days were reported in 2 months within the growing season. Nonepidemic years were associated with less than 10 cloudy days. Similar estimations for the United States depend on reliable estimations of inoculum availability and cloudiness.

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