EFFECTS OF WETNESS PERIOD AND TEMPERATURE ON DEVELOPMENT OF DARK POD SPOT (ALTERNARIA-BRASSICAE) ON OILSEED RAPE (BRASSICA-NAPUS)

In controlled environment experiments, when oilseed rape pods or leave s were inoculated with spore suspensions of Alternaria brassicae, the maximum disease incidence (proportion of pods or leaves diseased) incr eased as wetness period after inoculation increased from 4 to 24h and as temperature increased to 20 degrees C. There was a clear relationsh ip between disease incidence on pods and incidence on leaves with the same wetness/temperature conditions. Logistic equations described the effects of wetness period after inoculation on disease incidence (numb er of pods or leaves infected) or disease severity (number of lesions on pods or leaves) using temperature-dependent and tissue-dependent pa rameters. The time from inoculation to the appearance of the first les ions was shorter on pods than on leaves at temperatures less than or e qual to 15 degrees C and wetness periods less than or equal to 12 h. T wo-dimensional response surface equations or simple interpolations fro m one-dimensional equations were used to develop contour maps of expec ted disease incidence and severity, respectively, on leaves or pods to estimate the effects of different combinations of wetness period duri ng infection and temperature on disease development.