Effects of environmental factors on development of Pyrenopeziza brassicae (light leaf spot) apothecia on oilseed rape debris.

The development of Pyrenopeziza brassicae (light leaf spot) apothecia was s tudied on petiole debris from artificially infected oilseed rape leaves inc ubated at temperatures from 6 to 22 degreesC under different wetness regime s and in 16 h light/8 h dark or continuous darkness. There was no significa nt difference between light treatments in numbers of apothecia that develop ed. Mature apothecia developed at temperatures from 5 to 18 degreesC but no t at 22 degreesC. The rate of apothecial development decreased as temperatu re decreased from 18 to 5 degreesC; mature apothecia were first observed af ter 5 days at 18 degreesC and after 15 days at 6 degreesC. Models were fitt ed to estimates of the time (days) for 50% of the maximum number of apothec ia to develop (t(1); model 1, t(1) = 7.6 + 55.8(0.839)(T)) and the time for 50% of the maximum number of apothecia to decay (t(2); model 2, t(2) = 24. 2 + 387(0.730)(T)) at temperatures (T) from 6 to 18 degreesC. An interrupti on in wetness of the petiole debris for 4 days after 4, 7, or 10 days of we tness delayed the time to observation of the first mature apothecia for app roximate to4 days and decreased the number of apothecia produced (by compar ison with continuous wetness). A relationship was found between water conte nt of pod debris and electrical resistance measured by a debris-wetness sen sor. The differences between values of tl predicted by model 1 and observed values of t(1) were 1 to 9 days. Model 2 did not predict t(2); apothecia d ecayed more quickly under natural conditions than predicted by model 2.