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11

Epidemiology of soybean rust (Phakopsora pachyrhizi) in soybean (Glycine max) sentinel plots in Florida

Presenter: H. M. Young

All authors and affiliations: H. M. YOUNG (1,2), J. J. Marois (2), D. L. Wright (2), D. F. Narvaez (3), G. K. O’Brien (2). (1) University of Florida, Gainesville, FL; (2) University of Florida, NFREC, Quincy, FL; (3) Monsanto, St. Louis, MO

Since the discovery of soybean rust (SBR) in 2004 in the southeastern United States, its severity has been variable from year to year. Still, it is important to understand the epidemiology of the pathogen in Florida as it may serve as an inoculum source for other areas of the country. This study examined the incidence and severity of SBR in relation to prevailing weather data, growth stage, and maturity group (MGIII, MGV, MGVII) in soybean plots (15 m square) across the Panhandle of Florida that were part of the national sentinel plot network from 2005 through 2008. Of the three maturity groups, the MGIII soybean became infected first the least often. Plots became infected first at growth stage R4 (full pod) or later. On average, plots became infected 40 days earlier and 30 days closer to planting in 2008 than in 2005. Precipitation was the principle factor affecting disease progress, in which disease increased rapidly after rain events and was suppressed during dry periods. The area under the disease progress curves (AUDPC) for incidence was the lowest in 2007, most likely due to dry conditions. In 2008, there was a significant increase in disease incidence and severity as reflected in the AUDPC. This was associated with the occurrence of Tropical Storm Fay, which deposited up to 290 mm of water in the plot locations during the third week of August. Results from this study may lead to a better understanding of the impact of weather on the epidemiology of this pathogen.

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