B. D. L.
First and second authors: Institute of Arable Crops Research, Rothamsted, Harpenden, Herts AL5 2JQ, U.K.; and third author: Wye College, University of London, Ashford, Kent TN25 5AH, U.K.
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Accepted for publication 10 January 2001.
The development of Pyrenopeziza brassicae (light leaf spot) apothecia was studied on petiole debris from artificially infected oilseed rape leaves incubated at temperatures from 6 to 22°C under different wetness regimes and in 16 h light/8 h dark or continuous darkness. There was no significant difference between light treatments in numbers of apothecia that developed. Mature apothecia developed at temperatures from 5 to 18°C but not at 22°C. The rate of apothecial development decreased as temperature decreased from 18 to 5°C; mature apothecia were first observed after 5 days at 18°C and after 15 days at 6°C. Models were fitted to estimates of the time (days) for 50% of the maximum number of apothecia to develop (t1; model 1, t1 = 7.6 + 55.8(0.839)T) and the time for 50% of the maximum number of apothecia to decay (t2; model 2, t2 = 24.2 + 387(0.730)T) at temperatures (T) from 6 to 18°C. An interruption in wetness of the petiole debris for 4 days after 4, 7, or 10 days of wetness delayed the time to observation of the first mature apothecia for ≈4 days and decreased the number of apothecia produced (by comparison with continuous wetness). A relationship was found between water content of pod debris and electrical resistance measured by a debris-wetness sensor. The differences between values of t1 predicted by model 1 and observed values of t1 were 1 to 9 days. Model 2 did not predict t2; apothecia decayed more quickly under natural conditions than predicted by model 2.
The American Phytopathological Society, 2001