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Poster Presentations


Poster Presentations


Effects of night length and shade on the initial establishment of Asian soybean rust

Presenter: A. P. S. Dias

All authors and affiliations: A. P. S. DIAS (1), X. B. Yang (1), P. F. Harmon (2), and C. L. Harmon (2). (1) Iowa State University, Department of Plant Pathology, Ames, IA; and (2) University of Florida, IFAS Plant Pathology, Gainesville, FL

Field observations have suggested the association of Asian soybean rust (ASR) development with shade. Unlike many other rusts, ASR infection is initially observed on the abaxial surface of lower canopy leaves. In kudzu, the disease is more frequently observed on shaded plants compared to open-field ones. Regional outbreaks in Brazil are correlated to rain days during the previous month, which is possibly related to the shade effect by rain clouds. In Asia, the disease is more prevalent in long-night seasons (fall and spring). We hypothesize that a longer night period is necessary for infection, especially when complemented with shade in the following days. Studies were carried out at the University of Florida (Gainesville, FL, 2006) to determine the effects of night length after inoculation and daytime shading on ASR. One-month-old soybeans were inoculated at three times during the night (INOCTIME: 21 h, 00 h, and 02 h). The plants were covered with a shade cloth in different mesh sizes to obtain four light intensity levels (LIL): 100% (L1), 70% (L2), 50% (L3), and 20% (L4) of natural sunlight for 12 days until evaluation. There was no effect of INOCTIME on ASR incidence and severity. Treatments receiving partial light (L2, L3, and L4) had an incidence and severity higher than those in full light (L1). These results suggest that sunlight may affect ASR infection and initial establishment. ASR outbreaks may be related to cloudiness due to the reduction in light intensity.

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