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Poster Presentations

Poster Presentations


Effects of post-dew period temperature and relative humidity on urediniospore production

Presenter: M. Bonde

All authors and affiliations: M. BONDE (1), D. Berner (1), S. Nester (1). (1) USDA ARS, Frederick, MD

Soybean plants, cv. Williams, were inoculated with urediniospores of Phakopsora pachyrhizi, incubated overnight in a 20C dew chamber, and transferred to temperature-controlled growth chambers mimicking day/night temperature profiles representative of the U.S. soybean production areas during spring, summer, and fall. At 3-day intervals beginning 14 DAI, urediniospores were collected from each plant and counted. At the end of each experiment, numbers of lesions and leaf areas were determined for each leaf. Numbers of lesions per cm2 and urediniospores per plant and per lesion were calculated for each temperature profile. Leaflets from each plant were stained, and average numbers of uredinia per lesion and uredinium diameters were determined. The most urediniospores per lesion were produced when the day temperature peaked at 25C and the night temperature dipped to 12C. When day temperatures peaked at 29, 33, or 37C, urediniospores per plant were reduced to 41, 7, and 0.1%, respectively, of that at the optimum. The most lesions were produced when the temperature peaked at 25C and uredinia per lesion, at 25 or 29C. Daily temperature data were obtained from NOAA for a 4-year period for selected areas of the United States. While temperatures of the Midwestern states were usually conducive for urediniospore production during May through September, temperatures for the southern states commonly peaked above 33C during July and August, suggesting that high day temperatures limit sporulation. Post-dew period relative humidity had limited effect on urediniospore production.

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