Effects of temperature and rainfall on date of release of ascospores ofLeptosphaeria maculans(phoma stem canker) from winter oilseed rape (Brassica napus) debris in the UK

Abstract

AbstractData from a controlled environment experiment investigating effects of temperature on maturation ofLeptosphaeria maculanspseudothecia were used to derive equations describing the times until 30% or 50% of pseudothecia were mature as a function of temperature. A wetness sensor was developed to estimate the oilseed rape debris wetness and operated with debris exposed in natural conditions in 2000 and 2001. The maturation ofL. maculanspseudothecia on debris and concentrations of airborneL. maculansascospores were observed from 1999 to 2004. There were considerable differences between years, with the first mature pseudothecia observed in September in most years. There were linear relationships between the first date when 10% of maximum ascospore release was observed and the dates when 30% or 50% of pseudothecia were mature. By summing the daily temperature‐dependent rate of pseudothecial maturation for days after 1 August with rainfall >0.5 mm, the dates when 30% or 50% of pseudothecia were mature were predicted. There was good agreement between predicted and observed dates when 30% or 50% of pseudothecia were mature. These equations for predicting the timing ofL. maculansascospore release could be incorporated into schemes for forecasting, in autumn, the severity of phoma stem canker epidemics in the following spring/summer in the UK.