Submitted to: National Soybean Rust Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 11/14/2006
Publication Date: 11/26/2006
Citation: Beck, L.F., Miles, M.R., Steinlage, T.A., Hartman, G.L. 2006. Urediniospore Release and Escape from Rust-Infected Soybean Fields. National Soybean Rust Symposium. Interpretive Summary:
Technical Abstract: Phakopsora pachyrhizi, soybean rust, has infected soybeans in the continental United States from 2004-2006. This study monitored release, dispersal, and germination rates of soybean rust spores produced from epidemics at various stages of development using rotorods, passive traps, and water agar plates, respectively, at three locations for 6-10 days each in 2005. Rotorod samples were collected daily at 2 hr intervals from 08:00 to 18:00, with each sampling interval lasting 30 min. Passive trap samples were collected at 24 hr intervals. Spores were collected onto water agar plates to estimate germination rates in the lower, mid, and upper canopy at 10:00, 14:00, and 18:00. Enumerating spores on rods indicated a typical pattern of spore release and escape over the course of a day. In the morning, before dew dried, spore release was minimal. However, spore release increased after leaves dried, peaked during midday, then tapered off toward the evening. Rainfall events drastically reduced spore release for a 24-48 hr period. Spores enumerated on passive trap slides indicated that spores dispersed in the direction of prevailing winds at lower than expected rates (3 of 22 observation days). Spores collected on water agar plates germinated at rates ranging from 0.8% to 99% with an average of 52%. Though varying widely with epidemic severity, crop phenology, and environmental factors, daily spore release patterns, escape and dispersal of spores from the canopy, and germination rates are important in developing and improving forecasting models that predict soybean rust outbreaks.