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Reference Report for IND20379087
Title:Effects of duration, frequency, and temperature of leaf wetness periods on soybean rust.
Authors:Melching, J.S., Dowler, W.M., Koogle, D.L., Royer, M.H.
Source:Plant Dis. 1989, 73(2):117-122
Abstract:On soybean leaves at 20 C in the dark, uredospores of Phakopsora pachyrhizi began germinating 1.5 hr after dew was provided and reached a maximum level after 6-7 hr. Susceptible soybeans inoculated with viable uredospores developed no rust at dew period less than 6 hr. At 6 hr, trace levels of primary rust lesions developed at 18, 20, 23, and 26.5.degree.C. After 8 hr of dew at 18-26.5 C, lesion intensities were 10-fold higher than those at 6 hr at the corresponding temperatures. Increasing dew duration from 12 to 16 hr resulted in no signification increase in rust intensity, even at the most favorable temperatures (18-26.5 C). No lesions developed at 9 and 28.5 C, even with dew periods as long as 20 hr. Uredospores on unwetted soybean leaves progressively lost infectivity during sunshine conditions, but exhibited enhanced infectivity during 1 or 2 days on dry foliage under cloudy conditions. After 8 days foliage, no uredospores caused lesions following a 12-hr dew period at 18 C. Spores on leaves exposed to 4 or 6 hr of dew followed by drying for up to 4 days were able to infect when a 12-hr dew period was provided, but were 50% or less as infectious as similar spores that had not been exposed to brief initial wetting. Uniformly inoculated soybean plants given initial dew and then receiving dew every third, sixth, or ninth day after inoculation until maturity developed fewer lesions per square centimeter and higher yields with decreasing frequency of dew. Rust reducted numbers of filled pods, numbers of seeds per pod, and mean seed weight






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